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A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases
Accepted Manuscript Title: A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases Authors: Xiaojie Zhao, Kaifeng Tan, Jun Xing PII: DOI: Reference:
S0021-9673(18)31528-0 https://doi.org/10.1016/j.chroma.2018.12.021 CHROMA 359883
To appear in:
Journal of Chromatography A
Received date: Revised date: Accepted date:
16 August 2018 30 November 2018 10 December 2018
Please cite this article as: Zhao X, Tan K, Xing J, A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases, Journal of Chromatography A (2018), https://doi.org/10.1016/j.chroma.2018.12.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases Xiaojie Zhao a, Kaifeng Tan a,b, Jun Xing a,*
Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education),
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a
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, China b
The 718th Research Institute of CSIC, Handan, Hebei 056027, China
Corresponding author. Tel.: +86 15327201697. E-mail address: [email protected]
Highlights:
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A novel synthesis strategy of ionic liquid bonded polysiloxanes was proposed. 15 polymers differing in chemical structure have been synthesized. Most of the capillary columns have high column efficiency over 3000 plates/m. Each column provides quite different interaction features. The general polarity indexes of the columns fall in a broad range from 218 to 717.
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Abstract
Ionic liquid bonded polysiloxanes (PILs) are a class of polysiloxanes whose side chains contain
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ionic liquid (IL) moieties. Considering their excellent selectivity and thermo-stability, PILs have
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great potentials in the development of polar stationary phases for gas chromatography. In this paper, a novel synthesis strategy for PILs is proposed to diversify PIL stationary phases and also facilitate the study on relationships between stationary phase structure and separation
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performances. The polysiloxane with imidazole groups at the side chains was synthesized firstly, and then these imidazole groups further reacted with halogenated compounds to produce various
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IL groups. Upon this, fifteen PIL stationary phases differing in IL content, IL group or combination of different IL groups have been synthesized and used to prepare capillary columns
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through static coating method. These columns have quite different general polarity indexes (the average value of all Rohrschneider-McReynolds constants in this paper) falling in a broad range from 218 to 717, and most columns have column efficiency values over 3000 plates/m. In addition, IL content, structure of the IL and combination of different IL groups have noticeable influences on interaction features of the stationary phases. After that, the separation performances of these PIL stationary phases were demonstrated by separating various mixed samples of aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. In order to reveal the 1
relationship of interaction characteristics and separation performances, a set of indexes of contribution rates (CRs) is proposed. Based on CRs, the separation selectivity of the PIL stationary phases has been discussed in detail. The results indicate that there are significant differences in the separation selectivity not only between PILs and conventional polar stationary phases, but also among different PILs. All of these imply a family of practical PILs with special
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selectivity could be constructed upon this synthesis strategy. Keywords: Ionic liquid; Polysiloxane; Synthesis; Stationary phase; Gas chromatography 1. Introduction
Ionic liquids (ILs) are a class of organic molten salts whose melting points are below the boiling point of water [1], and a polymer with IL species in its repeating units is usually termed as
polymeric ionic liquid [2]. Due to the unique performances, these ionic liquids have been applied in many investigations, including electrochemical energy materials [3,4], stimuli-responsive
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materials [5,6], organic synthesis solvents [7,8], catalytic materials [9,10], separation materials
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[11,12], and so on.
As early as 1959, the first application of ILs in gas chromatography was published [13]. After
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that, a series of ILs have been synthesized and used as stationary phases for gas chromatography
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[14-20]. However, these ILs could not be used as qualified stationary phases due to their poor thermo-stability and weak resistance to moisture and other oxide impurities until the emergence of imidazolium-based ILs [21]. In the past decades, a variety of practical ionic liquid stationary
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phases have been investigated, and Supelco company has launched seven commercially available
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ones for gas chromatography since 2008. Current ionic liquid stationary phases could be roughly classified into three categories, micro-molecular, blending and polymeric ionic liquid stationary phases.
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The micro-molecular ionic liquid stationary phases include single-cationed [22-24], di-cationed [25,26] and multi-cationed [27,28] micro-molecular ILs. They are routinely synthesized via
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quaternization and metathesis [29]. Compared with single-cationed ILs, di-cationed and multi-cationed ILs usually exhibit better thermo-stability.
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The blending ionic liquid stationary phases refer to the mixture of two ionic liquids [30] or of
an ionic liquid and a conventional stationary phase like OV-1701 [31]. Blending is an effective way to acquire a new stationary phase with improved performances, but the durability is not undisputed. The polymeric ionic liquid stationary phases can be further classified into two categories by the location of IL moieties, at the side chains or the main chain. Two approaches have been proposed for the synthesis of the former ones. (1) Polymerization of vinyl ionic liquids. Initiated by AIBN, 2
some vinyl imidazolium [32,33] or phosphonium [34] ILs have been used to synthesize polymeric stationary phases with IL moieties at side chains. (2) Polymer modification. Two synthesis routines have been proposed as follows. One routine [35,36] is that a polysiloxane with side chains of 3-chloropropyl groups is synthesized and then react with 1-methylimidazole via quaternization reaction to form IL moieties at side chains. The obtained stationary phases not only
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inherit the character of "dual nature" from ILs, but also inherit the excellent film-forming ability from polysiloxanes. The other is based on hydrosilylation reaction of hydrogen silicone oil with vinyl ionic liquids [37]. As for polymeric stationary phases with IL moieties at main chains, 1-(3-chlorohexyl) imidazole [12] can be used to produce a polymer through consecutive
quaternization reactions. If N-vinylimidazole is employed to cap the terminal Cl atoms at the
polymeric ionic liquid, this kind of polymer can further polymerize through radical reaction of the vinyl groups.
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ILs are also called "designer solvents" [38], and it is because their properties can be tuned by
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varying the chemical structure of cation or anion moieties. Considering the principle of chromatography, that implies IL modification will bring us a great opportunity to develop some
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stationary phases with special selectivity. In this paper, a convenient and applicable synthesis
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strategy of ionic liquid bonded polysiloxanes (PILs) is proposed as follows: firstly, the polysiloxane with imidazole groups at the side chains is synthesized as a modifying platform; secondly, these imidazole groups further react with various halogenated compounds through
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quaternization to produce a big family of PILs. Upon this approach, we have obtained fifteen PIL
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stationary phases differing in IL content, IL group or combination of different IL groups. After they were used to prepare capillary columns through static coating, the column efficiencies and durability were tested. Then the approach of Rohrschneider-McReynolds constants were used to
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measure their column polarity. It was resulted that the general polarity indexes of the obtained columns fall in the range from 218 to 717. And IL content, structure of the IL and combination of
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different IL groups have noticeable influences on interaction features of the stationary phases. Finally, the PIL stationary phases were tested chromatographically using a series of mixed
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samples including aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. And the separation selectivity of them was compared to that of conventional polar columns TG-17ms and Elite-waxetr. It suggests that upon this synthesis strategy, we can acquire abundant PIL stationary phases with especial separation selectivity. 2. Experimental 2.1 Apparatus and Reagents All the GC analyses were carried out using a FULI 9710 gas chromatograph equipped with 3
flame ionization detector (FULI INSTRUMENTS, China). Nitrogen was used as the carrier gas with a flow rate of 0.4 mL/min for 10 m long columns and 1.0 mL/min for 30 m long columns. The injector and detector temperatures were set at 280 oC, the make-up flow of nitrogen at 30 mL/min, the hydrogen flow at 35 mL/min and the air flow at 350 mL/min. Methane was used as the dead time marker. FI-IR analysis was performed on a Thermo Nicolet 670 instrument (Thermo,
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USA), and 1HNMR analysis on a Mercury VX-300 instrument (300MHz, Varian, USA). Imidazole, sodium hydroxide, sodium iodide, acetone, tetrahydrofuran, potassium hydroxide, thionyl chloride, chloroform, acetonitrile and diethyl ether were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 3-Chloropropylmethyldiethoxysilane were purchased from Jianghan Fine Chemical Co., Ltd. (Jingzhou, China). Lithium
bis(trifluoromethanesulfonylimide) (LiNTf2), dimethyldiethoxysilane (DMDES),
hexamethyldisiloxane (HMDSO), 1-bromooctane, 1-bromododecane, 1-bromooctadecane,
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1-bromo-3-methylbutane, 1-bromo-3-phenylpropane, 3-chloro-1,2-propanediol,
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11-bromo-1-undecanol and 4-bromobutyronitrile were purchased from Aladdin Industrial Corporation (Shanghai, China). Benzene, n-butanol, 2-pentanone, 1-nitropropane, pyridine and all
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of the analytes for the selectivity test were purchased from J&K Scientific Ltd. (Beijing, China).
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3-Chloropropylmethyldiethoxysilane is technical grade and was purified by distillation before use. All the other reagents are analytical grade. 2-(2-(2-(2-Chloroethoxy)ethoxy)ethoxy)ethanol used in this paper was synthesized according to the reference [39]. The bare fused-silica capillary tube
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with a protecting polyimide coating (0.25 mm i.d.) was purchased from Yongnian Optical Fiber
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Factory (Hebei, China). The TG-17ms column (30 m × 0.25 mm i.d., film thickness 0.25 μm) was purchased from Thermo Scientific (USA), and its column efficiency is 2675 plates/m (naphthalene, k = 7.74, 120 oC). The Elite-waxetr column (30 m × 0.25 mm i.d., film thickness 0.25 μm) was
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purchased from PerkinElmer Life and Analytical Sciences (USA), and its column efficiency is 4205 plates/m (naphthalene, k = 6.40, 120 oC).
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2.2 Synthesis of the PILs The synthesis routine of the PILs is showed in Fig. 1. And the detailed supplementary
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information is listed in the Supplementary Material. 2.2.1 Synthesis of Imidazole Bonded Polysiloxanes (PSO-IMs) The synthesis of PSO-IMs roughly comprises two steps, synthesis of N-(3-propylmethyldiethoxysilane)imidazole (C3) and polycondensation of C3 with dimethyldiethoxylsilane (DMDES). After sodium imidazolide (C1) and 3-iodopropylmethyldiethoxysilane (C2) were synthesized according to the references [40] and [41] respectively, C3 was synthesized by the reaction of C1 4
with C2 according the reference [42]. The synthesis procedures of C1, C2 and C3 are presented in the Supplementary Material. General synthesis procedures for PSO-IMs: KOH aqueous solution was added dropwise to a mixture of C3 and DMDES. After stirring at 80 oC for 12 h, the formed ethyl alcohol was removed from the reaction mixture under vacuum. Hexamethyldisiloxane (HMDSO) was added and then,
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the reaction temperature was raised to 105 oC and kept for another 48 h. An oil-water separator was used to remove the ethyl alcohol and water formed during this reaction process. The resultant was dissolved in chloroform (20 mL) and then washed with water till neutrality. After chloroform was removed under reduced pressure, a PSO-IM was obtained as a light yellow viscous liquid.
By changing the ratio of C3 to DMDES, we have synthesized three kinds of polysiloxanes with different imidazole contents termed respectively as PSO-IM(7.8%), PSO-IM(16%) and
PSO-IM(33%). The imidazole content in this paper refers to the percentage of imidazole units in
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total units. The amount of reactants and products is listed in Table 1.
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2.2.2 Synthesis of the PILs
PSO-IMs react with halogenated compounds to form PILs. Different halogenated compounds
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lead to different substituent groups at 3- position of the imidazole ring, namely different IL groups.
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Two sets of PILs have been synthesized in this work. One bears only one type of IL groups and is named as Mono-PIL. The other bears two types of IL groups and is named as Bi-PIL. In this paper, "substituent group" refers to the group at the 3- position of the imidazole ring except especial
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Material), respectively.
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definition. The detailed synthesis information is listed in Table S2 and Table S3 (Supplementary
2.2.2.1 Synthesis of the Mono-PILs General procedure: A certain amount of PSO-IM (e.g. PSO-IM(16%)) and a halogenide (e.g.
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1-bromo-3-methylbutane) were dissolved in dried organic solvent 1 (e.g. chloroform), and the solution was stirred under nitrogen and heated to reflux. 48 h later, solvent 1 was evaporated under
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vacuum. The residue was washed with solvent 2 (e.g. n-hexane) to remove the unreacted halogenide. Then the crude product was dissolved in 3 mL dried solvent 3 (e.g. ethanol) and a
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solution of NTf2Li in dried solvent 3 was added. The mixture was stirred for 24 h at room
temperature. After that, solvent 3 was evaporated under vacuum. The residue was redissolved in chloroform and washed with water until halide ions could not be found by silver nitrate test. At last, chloroform was removed under reduced pressure and a Mono-PIL (e.g. PIL-iC5(16%)) was obtained as a light yellow viscous liquid. 2.2.2.2 Synthesis of the Bi-PILs General procedure: A certain amount of R1X (e.g. 1-bromooctane) and PSO-IM (e.g. 5
PSO-IM(16%)) were added to dried acetonitrile. The mixture was stirred under nitrogen at 80 oC for 48 h. Then, a certain amount of R2X (e.g. 4-bromobutyronitrile) was also added to this reaction solution, and the temperature was kept at 80 oC for another 48 h. Then NTf2Li in dried acetonitrile was added and the mixture was stirred for 24 h at room temperature. After the solvent of acetonitrile was evaporated, solvent 1 (e.g. n-hexane) and solvent 2 (e.g. diethyl ether) were used
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successively to wash away the unreacted R1X and R2X from the residue. After that, the residue was redissolved in chloroform and washed with water until halide ions could not be found by
silver nitrate test. Finally, chloroform was removed under reduced pressure and a Bi-PIL (e.g. PIL-C8&CN) was obtained as a light yellow viscous liquid. 2.3 Preparation of Capillary Columns
Before coating, each bare fused-silica capillary tube (11 m × 0.25 mm i.d.) was rinsed with 20
mL methanol and 20 mL dichloromethane successively. After that, the capillary tubes were purged
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with nitrogen gas, and conditioned from 50 to 260 oC at 2 oC/min and held at 260 oC for 3 h. Then
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the capillary tubes were statically coated using 0.30% (w/v) of stationary phases dissolved in dichloromethane (for PIL-C8(16%), PIL-C12(7.8%), PIL-C12(16%), PIL-C12(33%),
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PIL-C18(16%), PIL-PP(16%), PIL-C8&PP, and PIL-C8&CN) or in methanol (for the other PILs).
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The coated capillary columns were purged with nitrogen gas and conditioned under the following temperature program: 50 oC for 1 h firstly, then increased to 200 oC at 1 oC/min and held for 1 h, and finally increased to the conditioning temperature of each column at 1 oC/min and
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held for 3 h. The obtained columns were cut to about 10 m, sealed with septa at the column ends
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and kept in the desiccator before use. Eq. (1) can be used to approximately calculate the stationary phase film thickness (df) of capillary columns [34,43].
⁄400
(1)
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Where dc is the diameter of the capillary tube (in micrometer), and c is the percentage concentration by weight (w/v, %) of the solution of a stationary phase.
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In this work, dc= 250 μm, and c is set to be 0.30% (w/v), therefore the theoretic film thickness is
about 0.188 μm for each home-made capillary column.
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3. Results and discussion 3.1 1HNMR Characterization 1
HNMR has been used to demonstrate the structures of all synthetic products, including C1～
C3, PSO-IMs and PILs. And all of the data are listed in the Supplementary Material. In the spectrums of PSO-IMs, the ratio of the integral intensity of H at 0.05 ppm (assigned to CH3 on the Si atoms) and that at 7.47 ppm (assigned to C2-H of the imidazole rings) was used to roughly calculate the imidazole content of each PSO-IM. The calculating equation is shown as Eq. 6
(S1) in the Supplementary Material. And the imidazole contents of the three PSO-IMs are 7.8%, 16% and 33%, respectively. For all PILs, the actual contents of IL groups are in accordance to the imidazole contents of the PSO-IMs used approximately, demonstrated by 1HNMR data. So the bracketed percentages of PILs also refer to the ionic liquid contents. For the three Bi-PILs, the ratio of different IL groups
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was deduced from the integral intensity of characteristic H of the substituent groups at the 1- or 3positions of the imidazole rings. The calculating equations are given in the Supplementary
Material as Eq. (S2), Eq. (S3) and Eq. (S4), respectively. And the calculated ratios are 2:1 (C8/PP), 3:1 (CN/PP) and 1:1 (C8/CN), respectively. 3.2 FT-IR
The fifteen PILs have been characterized by FT-IR (Fig. 2, Fig. S2～S4 in the Supplementary Material). These spectra show some features in common because all these PILs comprise of a
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polysiloxane skeleton and some side chains with imidazolium based IL moieties. The band at 1265
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cm-1 demonstrates the presence of Si-C groups, and the bands at 1050 and 803 cm-1 demonstrate that of Si-O-Si in polysiloxanes. The evidences of IL moieties are as follows, bands between 3085
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and 3148 cm-1 are assigned to unsaturated C-H stretching, and band at 1567 cm-1 is assigned to
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skeleton stretching of the imidazole ring. Among the fifteen FT-IR spectra, only those of PIL-iC5(16%), PIL-C8(16%), PIL-C12(7.8%), PIL-C11-OH(16%), PIL-CN(16%), PIL-TG(7.8%) and PIL-TG(16%) show strong and broad bands in the range between 1632 and 1647 cm-1 and the
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range between 3300 and 3500 cm-1, implying the existence of the adsorbed water.
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For the PILs with the same IL group but different IL contents, the FT-IR spectra exhibit some differences, seeing Fig. 2A. With the increase of IL content, the intensity of unsaturated C-H stretching vibration increases, and so do that of saturated C-H stretching vibration (2850～2965
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cm-1, partly attributed to the substituent groups). For the PILs with the same IL content but different IL groups, in most cases, their FT-IR spectra
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look very alike due to the bands overlap of the substituent groups regardless of the differences in
intensity of the saturated C-H stretching, seeing Fig. S2～S4 in the Supplementary Material.
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Additionally, the characteristic absorption peaks for the substituent groups in the Mono-PILs
are also demonstrated in the FT-IR spectra of the corresponding Bi-PILs, seeing Fig. 2B. 3.3 Column efficiency and durability The column efficiency, retention factor and tailing factor were measured at 100 oC using
naphthalene and listed in Table 2. Each column was always operated below its conditioning temperature and has usually experienced no less than 700 injections within a whole evaluation process. 7
Table 2 shows that except PIL-TG(7.8%) and PIL-C3-2OH(16%), most of the columns possess good thermal stability and their conditioning temperatures are not lower than 280 oC. Six alkyl Mono-PILs and three Bi-PILs own the best thermal stability since their conditioning temperatures are up to 300 oC or even higher. As the test of baseline bleeding can reflect the loss of a stationary phase during a practical application, the baselines of the whole PIL columns have been recorded
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within the range from 100 to 400 oC at the rate of 3 oC·min-1 and shown in Fig. S5 (Supplementary Material). As shown in Fig. S5, most of the PIL stationary phases start to bleed after 270 oC.
Among these stationary phases, PIL-C8&PP, PIL-C18(16%) and PIL-C12(33%) start to bleed around 300 oC, and they own the highest thermal stability. On the other hand, most alkyl
Mono-PILs and all Bi-PILs have higher column efficiencies. And their column efficiencies and retention factors change little after a test period of six months. These demonstrate that alkyl Mono-PILs and Bi-PILs have good durability.
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Since all of the stationary phase solutions for static coating have the same concentration, all
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home-made capillary columns have the same film thickness theoretically [44]. Therefore, the retention factors showed in Table 2 primarily reveal the interaction strength between naphthalene
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and the stationary phases differing in IL structure or IL content. When the IL groups are the same,
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the retention factors increase gradually as the IL content increases; when the IL contents are the same and the substituent groups are n-alkyl groups, the retention factors also increase with the increase of carbon numbers of the n-alkyl groups. Moreover, Bi-PILs afford larger retention
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factors than the corresponding Mono-PILs.
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Table 2 also exhibits that the tailing factors of all columns are close to 1 except PIL-PP(16%). This indicates that most films obtained by static coating are uniform. PIL-PP(16%) is quite different from the other stationary phases and its tailing factor is excessively large (1.51 and 1.73).
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This might be attributed to the excessively strong interactions between naphthalene and PIL-PP(16%), which may be explained further by the principle of "like dissolves like".
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3.4 Column polarity
Polarity is generally used to describe the overall capacity of a stationary phase for all possible
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intermolecular interactions [45]. It is commonly characterized by the sum of five Rohrschneider-McReynolds constants, or the arithmetic average of the constants, termed as "general polarity index" (GPI) [46]. This approach was put forward by Rohrschneider in 1966 [47] and improved by McReynolds in 1970 [48]. Such constants as X', Y', Z', U' and S' represent five specific interactions between a stationary phase with the solutes: X'- dispersive interactions; Y'-
proton donor and acceptor capabilities plus dipolar interactions; Z'- dipolar interactions plus weak proton acceptor, but not proton donor capabilities; U'- dipolar interactions; and S'- strong proton 8
acceptor capabilities. Rohrschneider-McReynolds constants and GPI (80 oC) of each PIL have been measured, and the data are exhibited in Table S4 (Supplementary Material). Upon our synthesis strategy, the obtained PILs afford quite different GPIs, ranging from 218 to 717. Both PIL-TG(7.8%) and PIL-C18(16%) have GPIs below 300, PIL-C12(33%), PIL-PP(16%) and three Bi-PILs between 300 and 400, four columns including PIL-C12(16%), PIL-iC5(16%),
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PIL-C3-2OH(16%) and PIL-CN(16%) between 400 and 500, and the other columns including PIL-C8(16%), PIL-C12(7.8%), PIL-TG(16%) and PIL-C11-OH(16%) above 500. As a
comparison, GPI of the conventional medium polar column of TG-17ms was measured to be 189, and that of the conventional strong polar column of Elite-waxetr 463 (also seeing Table S4).
Furthermore, these stationary phases offer quite different interaction features. PIL-C11-OH(16%) owns the largest Y' (930), Z' (906) and S' (1097), and PIL-TG(16%) and PIL-iC5(16%) offer the
largest X' (331) and U' (717), respectively. PIL-TG(7.8%) has the smallest X' (88), U' (228) and S'
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(200), and PIL-C18(16%) shows the smallest Y' (258) and Z' (235). When line diagrams were
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made using these data, we found some interesting relations between the chemical structures of the PILs and their interaction features or GPIs, seeing Fig. 3～5.
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Fig. 3 exhibits that if the substituent groups are non-polar groups like n-dodecyl, GPI decreases
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with the increase of IL content. But if the substituent groups are polar groups like tetraglycol, GPI increases with the increase of IL content. On the other hand, if the substituent groups are non-polar groups, Y' and Z' decrease with the increase of IL content, but if the substituent groups
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are polar groups, Y' and Z' increase with the increase of IL content. No matter the substituent
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groups are non-polar or polar, both U' and X' increase with the increase of IL content. These results imply that both the IL content and the polarity of the substituent groups are important factors to tune GPIs or interaction features of the PILs.
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Fig. 4 shows that, when the substituent groups are normal-alkyl groups (e.g. n-octyl, n-dodecyl or n-octadecyl), the reduction in the carbon numbers of n-alkyl groups leads to the increased GPIs
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or interaction features of the PILs. But when the substituent groups are isomerized alkyl groups (e.g. iso-pentyl), you will find an interesting result. Though the carbon number of iso-pentyl is less
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than that of n-octyl, PIL-iC5(16%) does not have a larger GPI than PIL-C8(16%) due to the
unexpected reduction in Y', Z' and S'. That means the configuration of a substituent group also has important effect on the GPIs or interaction features of the PILs. It had been supposed that the GPIs of the Bi-PILs would lie in between that of the corresponding Mono-PILs. In fact, some experimental results are unexpected. Fig. 5A～5C show that integrating two different IL groups into one stationary phase brings great changes to the GPIs of the Bi-PILs and some of their interaction features. The GPIs of most Bi-PILs are smaller than 9
that of the corresponding Mono-PILs. Among the five interaction features, U' and X' of the Bi-PILs are similar to that of the corresponding Mono-PILs. All Bi-PILs have much smaller S' than their corresponding Mono-PILs. As for Y' and Z', the Bi-PILs roughly lie in between the corresponding Mono-PILs. 3.5 Separation performances of the PIL stationary phases
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3.5.1 Aliphatic esters Fig. 6A～6D show the chromatograms of ten aliphatic esters on PIL-TG(7.8%), PIL-C8(16%) and two conventional polar columns (TG-17ms and Elite-waxetr). These aliphatic esters can be
categorized into three groups of isomers. Group 1: ethyl propionate and propyl acetate; group 2:
ethyl butyrate, isobutyl acetate and propyl propionate; group 3: the rest aliphatic esters tested. On the TG-17ms (GPI: 189) and Elite-waxetr (GPI: 463), there was a pair of co-eluting isomers
respectively. But on PIL-TG(7.8%) whose GPI is 218, between that of TG-17ms and Elite-waxetr,
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all of the aliphatic esters could be baseline separated. So we think the GPI of a stationary phase is
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not good enough to represent the separation selectivity towards aliphatic esters. In order to reveal the features based on a stationary phase’s characteristic interactions more exactly, herein we
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proposed an index termed as "contribution rate" (CR). It is derived from the rate of each polarity
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constant to the sum of five polarity constants of a stationary phase. Every stationary phase has five CRs. For example, CRX' = X'/(X'+Y'+Z'+U'+S'). Then, the selectivity of a stationary phase can be described by five indexes of CRi (i=X', Y', Z', U' or S'). Fig. 6E is the diagram of CR indexes of
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the four stationary phases mentioned above. Although there is a great difference between
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TG-17ms and Elite-waxetr in GPI, Fig. 6E clearly shows the two stationary phases are so similar, having four similar CR indexes except CRY'. This result may account for the similar drawback of these two stationary phases in the isomer separation, each having a pair of unresolved isomers. On
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the other hand, PIL-TG(7.8%) shows quite different CR indexes from that of TG-17ms and Elite-waxetr (Fig. 6E), and offers different or better separation ability to the isomers (Fig. 6A).
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Therefore, we think that CR index can be used to differentiate the separation performances of stationary phases.
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In fact, Fig. 6E not only reveals the great distinctions between the conventional stationary
phases and PIL ones on CR indexes, but also that between the two PIL stationary phases. Firstly, both PIL stationary phases have CRX' indexes below 10%, while the CRX' indexes of the two
conventional stationary phases are about 15%. Since dispersive interaction is not a key role in isomer separation, in our opinion, decreasing CRX' naturally leads to increased other CR indexes related to proton donor and acceptor capabilities and dipolar interactions. This may at least be part of the reason why both PIL stationary phases have better selectivity towards the tested isomers. 10
Secondly, for the two PIL stationary phases, there are also significant differences in CR indexes. PIL-C8(16%) has much larger CRS', but smaller CRU' and CRZ' than PIL-TG(7.8%). These differences are reflected on the selectivity of the stationary phases necessarily. The elution orders of two pairs of isomers (ethyl butyrate/ isobutyl acetate, isoamyl acetate/ propyl butyrate) are reverse on PIL-TG(7.8%) and PIL-C8(16%). In other words, PIL-C8(16%) can retain the ester of
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iso-alcohol stronger than retain that of n-alcohol, and PIL-TG(7.8%) does inversely. 3.5.2 Dichloro-anilines
Fig. 7A～7D show the chromatograms of six dichloroaniline isomers on PIL-C11-OH(16%), PIL-TG(16%) and two conventional polar columns (TG-17ms and Elite-waxetr), and Fig. 7E exhibits the diagram of CR indexes of these four stationary phases.
The tested dichloro-anilines could be separated well on the four columns, but considering the
short column lengths of the two PIL columns, it is reasonable to say that the PIL stationary phases
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offer better separation efficiency than TG-17ms and Elite-waxetr. Moreover, it is interesting the
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elution order of 2,4-dichloroaniline and 2,5-dichloroaniline on PIL-C11-OH(16%) is different from that on the other three stationary phases. As shown in Fig. 7E, except for CRY', the other four
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CR indexes of PIL-C11-OH(16%) are different from those of the other stationary phases.
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PIL-C11-OH(16%) affords much bigger CRZ' and CRS' than the other stationary phases. While Z' represents the dipolar interactions plus weak proton acceptor, but not proton donor capabilities, and S' represents the strong proton acceptor capabilities. On the other hand, since the predicted
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pKa of 2,4-dichloroaniline and 2,5-dichloroaniline are 2.02 ± 0.10 and 1.60 ± 0.10 respectively
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(SciFinder, https://scifinder.cas.org/scifinder/view/scifinder/scifinderExplore.jsf), 2,4-dichloroaniline should be a relatively stronger basic than 2,5-dichloroaniline and also a relatively stronger proton acceptor. Moreover, the CRS' and CRZ' of PIL-C11-OH(16%) are very
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salient, so it is not difficult to understand why 2,4-dichloroaniline was eluted after 2,5-dichloroaniline on PIL-C11-OH(16%).
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3.5.3 Alcohols
It was reported alcohols frequently formed tailing peaks on ionic liquid stationary phases, such
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as imidazolium-based [49] and phosphonium-based [24] ionic liquids, and polymeric imidazolium ionic liquids [50]. As shown in Fig. 8A, alcohols do show severe tailing peaks on PIL-iC5(16%), and iso-octanol is co-eluted with n-heptanol on this column. But on the PIL-C12(7.8%), PIL-TG(7.8%) and PIL-C18(16%), the alcohols are separated well and give symmetrical peaks, seeing Fig. 8B～8D. In addition to the improved coating performances, this may also be related to the unique interaction characteristics. 3.5.4 Other mixed samples 11
Besides the analytes mentioned above, some mixtures of aromatic amines, substituted alkanes, phthalic acid esters, nonane and its isomers, polycyclic aromatic hydrocarbons and n-alkanes have also been tested on the home-made PIL columns, seeing Fig. 9. The baseline separations are achieved for all of the analytes except for anthracene and phenanthrene (Fig. 9E). In summary, upon the synthesis strategy mentioned above, we can not only obtain the PIL
SC RI PT
stationary phases similar to the conventional polar stationary phases, but also acquire the PIL stationary phases with special separation selectivity. 4. Conclusions
In this paper, we put forward a novel synthesis strategy for PILs. Based on the synthesized
imidazole bonded polysiloxanes, abundant and readily available organic halogenides can be used to synthesize various PILs. Through this synthesis strategy, we have synthesized fifteen PILs
differing in IL content, IL group, or combination of different IL groups. Their GPIs fall in a broad
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range from 218 to 717. And the GPI and interaction features can be tuned by changing IL contents,
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chemical structures of IL groups and combinations of different IL groups. It was also resulted that most alkyl Mono-PILs and Bi-PILs own better thermal stability and durability. Moreover, different
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interaction characteristics of the different PIL stationary phases lead to their different separation
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selectivity for a variety of analytes including aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. So this synthesis strategy is beneficial to the development of polar stationary phases with good thermal stability and unique separation selectivity, and to
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ionic liquids as valuable stationary phases in gas chromatography: Chemical synthesis and full
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Figure captions: Fig. 1. Synthesis routine of the PILs. Reagents: (i) NaOH; (ii) NaI; (iii) THF; (iv) DMDES,
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HMDSO, KOH, H2O; (v) R1-X; (vi) R2-X; (vii) NTf2Li.
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Fig. 2. FT-IR spectra of PILs. (A) FT-IR spectra of PIL-C12(7.8%), PIL-C12(16%) and
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PIL-C12(33%). (B) FT-IR spectra of PIL-C8(16%), PIL-CN(16%) and PIL-C8&CN.
17
SC RI PT
Fig. 3. Diagram of Rohrschneider-McReynolds constants and GPIs against the IL contents. The
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A
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substituent groups are (A) n-dodecyl groups and (B) tetraglycol groups, respectively.
Fig. 4. Diagram of Rohrschneider-McReynolds constants and GPIs against the carbon numbers of
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the alkyl substituent groups.
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Fig. 5. Diagram of Rohrschneider-McReynolds constants and GPIs of the Bi-PILs and the
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A
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corresponding Mono-PILs. CX(%) refers to the proportion of X in the total units.
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Fig. 6. Chromatograms of aliphatic esters on (A) PIL-TG(7.8%), (B) PIL-C8(16%), (C) TG-17ms and (D) Elite-waxetr, and (E) diagram of CR indexes of these four columns. Peaks: 1. ethyl
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propionate; 2. propyl acetate; 3. isobutyl acetate; 4. ethyl butyrate; 5. propyl propionate; 6. isoamyl acetate; 7. propyl butyrate; 8. ethyl valerate; 9. butyl propionate; 10. n-amyl acetate. Temperature program for (A) and (D): 40 oC for 3 min, 10 oC·min-1 to 100 oC; for (B): 40 oC for 2
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min, 5 oC·min-1 to 100 oC; for (C): 40 oC for 3 min, 4 oC·min-1 to 100 oC.
19
SC RI PT U N A M D
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Fig. 7. Chromatograms of dichloro-anilines on (A) PIL-C11-OH(16%), (B) PIL-TG(16%), (C) TG-17ms and (D) Elite-waxetr columns, and (E) diagram of CR indexes of these four stationary phases. Peaks: 1. 2,6-dichloroaniline; 2. 2,5-dichloroaniline; 3. 2,4-dichloroaniline; 4.
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2,3-dichloroaniline; 5. 3,5-dichloroaniline; 6. 3,4-dichloroaniline. Temperature program for (A),
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(B) and (C): 10 oC·min-1 from 140 oC to 250 oC; for (D): 10 oC·min-1 from 140 oC to 220 oC.
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SC RI PT
Fig. 8. Chromatograms of alcohols on (A) PIL-iC5(16%), (B) PIL-C18(16%), (C) PIL-C12(7.8%) and (D) PIL-TG(7.8%). Peaks: 1. iso-propanol; 2. n-propanol; 3. iso-butanol; 4. n-butanol; 5.
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iso-pentanol; 6. n-pentanol; 7. n-hexanol; 8. cyclohexanol; 9. n-heptanol; 10. iso-octanol; 11.
n-octanol; 12. n-decanol; 13. n-undecanol; 14. n-dodecanol. Temperature program for (A) and (B):
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60 oC for 1.5 min, 30 oC·min-1 to 260 oC; for (C): 60 oC for 1.5 min, 30 oC·min-1 to 250 oC; for (D):
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60 oC for 1.5 min, 30 oC·min-1 to 240 oC.
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Fig. 9. (A) Chromatogram of the aromatic amines on PIL-CN&PP. Peaks: 1. N,N-dimethylaniline;
2. aniline; 3. o-toluidine; 4. o-chloroaniline; 5. 2,4-dimethylaniline; 6. 3,5-dichloroaniline; 7. 3,4-dichloroaniline; 8. diphenylamine; 9. o-nitroaniline; 10. 1-naphthylamine; 11. toluene-2,4-diamine; 12. m-nitroaniline; 13. p-nitroaniline. Temperature program: 120 oC for 1.5 min, 30 oC·min-1 to 230 oC. (B) Chromatogram of substituted alkanes on PIL-C8&CN. Peaks: 1. 1-bromobutane; 2. acetonitrile; 3. 1-bromine-3-methylbutane; 4. 1-chlorohexane; 5. 1-nitropropane; 6. 21
1-bromooctane; 7. 3-bromopropionitrile; 8. 4-bromobutyronitrile; 9. 1-bromo-3-phenylpropane; 10. 1-bromododecane. Temperature program: 40 oC for 2 min, 30 oC·min-1 to 260 oC. (C) Chromatogram of phthalic acid esters on PIL-TG(7.8%). Peaks: 1. dimethyl phthalate; 2. diethyl phthalate; 3. diisobutyl phthalate; 4. dibutyl phthalate; 5. bis(4-methyl-2-pentyl) phthalate; 6. diamyl phthalate; 7. bis(2-methoxyethyl) phthalate; 8. bis(2-ethoxyethyl) phthalate; 9. dihexyl
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phthalate; 10. bis(2-ethylhexyl) phthalate; 11. butylbenzyl phthalate; 12. bis(2-butoxyethyl) phthalate; 13. dicyclohexyl phthalate; 14. dioctyl phthalate; 15. dinonyl phthalate. Temperature program: 100 oC for 2 min, 20 oC·min-1 to 240 oC.
(D) Chromatogram of n-nonane and its isomers on PIL-C18(16%). Peaks: 1.
2,2,4,4-tetramethylpentane; 2. 2,2,4-trimethylhexane; 3. 3,3-dimethylheptane; 4.
2,3-dimethylheptane; 5. 4-ethylheptane; 6. n-nonane. Temperature program: 40 oC.
(E) Chromatogram of polycyclic aromatic hydrocarbons on PIL-C8&PP. Peaks: 1. naphthalene; 2.
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anthrene; 3. acenaphthene; 4. fluorene; 5. phenanthrene; 6. anthracene; 7. fluoranthene; 8. pyrene;
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9. benzo(a)anthracene; 10. chrysene; 11. benzo(b)fluoranthene; 12. benzo(k)fluoranthene; 13. benzo(a)pyrene; 14. indeno(1,2,3-cd)pyrene; 15. dibenzo(a,h)anthracene; 16. benzo(g,h,i)perylene.
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Temperature program: 40 oC for 1 min, 20 oC·min-1 to 150 oC, and then 10 oC·min-1 to 280 oC.
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(F) Chromatogram of 18 n-alkanes on PIL-C12(33%). Temperature program: 120 oC for 1 min,30 C·min-1 to 250 oC.
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o
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Tables: Table 1. Reactant and product information of PSO-IMs with different imidazole contents.
Product
PSO-IM(16%)
PSO-IM(33%)
C3 (g/mol)
2.42 / 0.010
2.42 / 0.010
2.42 / 0.010
DMDES (g/mol)
20.57 / 0.139
9.57 / 0.065
5.79 / 0.039
KOH (g)
0.97
0.46
H2O (mL)
15.5
6.5
0.46
HMDSO (g/mol)
0.12 / 0.00075
0.06 / 0.00038
0.038 / 0.00024
Mass (g)
7.18
3.37
2.56
Yield (%)
60
52
4.5
56
Table 2. Retention factors, tailing factors and column efficiencies. Conditioning
Tailing factor (Tf) a
Retention factor (k)
temperature (oC)
Initial
Six months later
PIL-iC5(16%)
300
3.83
3.70
PIL-C8(16%)
300
4.13
4.13
PIL-C12(7.8%)
300
3.66
3.25
PIL-C12(16%)
300
4.11
PIL-C12(33%)
310
7.22
PIL-C18(16%)
300
PIL-TG(7.8%)
250
(plates/m)
Six months later
0.99
0.98
3809
3609
0.97
1.09
3165
3175
0.98
0.96
3892
3643
3.91
0.97
0.95
2962
2606
7.12
1.16
1.10
3873
3614
6.32
6.27
0.98
0.97
3838
3916
3.13
3.06
0.99
0.95
3591
2583
280
4.23
3.12
1.01
1.24
2677
2413
280
2.90
2.79
1.51
1.73
3007
2776
D
M
A
N
Initial
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PIL-PP(16%)
Initial
Column efficiency
Six months later
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PIL-TG(16%)
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Stationary phase
SC RI PT
Reactant
PSO-IM(7.8%)
230
3.26
3.18
1.06
1.05
2544
2597
PIL-C11-OH(16%)
280
3.16
3.41
0.99
1.04
2909
2643
PIL-CN(16%)
280
3.62
3.57
1.01
1.07
3037
2895
PIL-C8&PP
300
6.65
6.54
0.97
0.99
3612
3720
PIL-CN&PP
300
4.48
4.39
0.96
0.95
3321
3527
A
CC
PIL-C3-2OH(16%)
PIL-C8&CN 300 5.78 5.87 0.99 1.04 4000 4047 a T f W 0.05 2 f , in this formula, W0.05 is the peak width at 5% height, and f is the front half-width measured from the leading edge to a perpendicular dropped from the peak apex. A tailing factor of 1 means a symmetric peak.
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S0021-9673(18)31528-0 https://doi.org/10.1016/j.chroma.2018.12.021 CHROMA 359883
To appear in:
Journal of Chromatography A
Received date: Revised date: Accepted date:
16 August 2018 30 November 2018 10 December 2018
Please cite this article as: Zhao X, Tan K, Xing J, A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases, Journal of Chromatography A (2018), https://doi.org/10.1016/j.chroma.2018.12.021 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases Xiaojie Zhao a, Kaifeng Tan a,b, Jun Xing a,*
Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of Education),
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a
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, Hubei 430072, China b
The 718th Research Institute of CSIC, Handan, Hebei 056027, China
Corresponding author. Tel.: +86 15327201697. E-mail address: [email protected]
Highlights:
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A novel synthesis strategy of ionic liquid bonded polysiloxanes was proposed. 15 polymers differing in chemical structure have been synthesized. Most of the capillary columns have high column efficiency over 3000 plates/m. Each column provides quite different interaction features. The general polarity indexes of the columns fall in a broad range from 218 to 717.
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Abstract
Ionic liquid bonded polysiloxanes (PILs) are a class of polysiloxanes whose side chains contain
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ionic liquid (IL) moieties. Considering their excellent selectivity and thermo-stability, PILs have
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great potentials in the development of polar stationary phases for gas chromatography. In this paper, a novel synthesis strategy for PILs is proposed to diversify PIL stationary phases and also facilitate the study on relationships between stationary phase structure and separation
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performances. The polysiloxane with imidazole groups at the side chains was synthesized firstly, and then these imidazole groups further reacted with halogenated compounds to produce various
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IL groups. Upon this, fifteen PIL stationary phases differing in IL content, IL group or combination of different IL groups have been synthesized and used to prepare capillary columns
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through static coating method. These columns have quite different general polarity indexes (the average value of all Rohrschneider-McReynolds constants in this paper) falling in a broad range from 218 to 717, and most columns have column efficiency values over 3000 plates/m. In addition, IL content, structure of the IL and combination of different IL groups have noticeable influences on interaction features of the stationary phases. After that, the separation performances of these PIL stationary phases were demonstrated by separating various mixed samples of aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. In order to reveal the 1
relationship of interaction characteristics and separation performances, a set of indexes of contribution rates (CRs) is proposed. Based on CRs, the separation selectivity of the PIL stationary phases has been discussed in detail. The results indicate that there are significant differences in the separation selectivity not only between PILs and conventional polar stationary phases, but also among different PILs. All of these imply a family of practical PILs with special
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selectivity could be constructed upon this synthesis strategy. Keywords: Ionic liquid; Polysiloxane; Synthesis; Stationary phase; Gas chromatography 1. Introduction
Ionic liquids (ILs) are a class of organic molten salts whose melting points are below the boiling point of water [1], and a polymer with IL species in its repeating units is usually termed as
polymeric ionic liquid [2]. Due to the unique performances, these ionic liquids have been applied in many investigations, including electrochemical energy materials [3,4], stimuli-responsive
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materials [5,6], organic synthesis solvents [7,8], catalytic materials [9,10], separation materials
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[11,12], and so on.
As early as 1959, the first application of ILs in gas chromatography was published [13]. After
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that, a series of ILs have been synthesized and used as stationary phases for gas chromatography
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[14-20]. However, these ILs could not be used as qualified stationary phases due to their poor thermo-stability and weak resistance to moisture and other oxide impurities until the emergence of imidazolium-based ILs [21]. In the past decades, a variety of practical ionic liquid stationary
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phases have been investigated, and Supelco company has launched seven commercially available
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ones for gas chromatography since 2008. Current ionic liquid stationary phases could be roughly classified into three categories, micro-molecular, blending and polymeric ionic liquid stationary phases.
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The micro-molecular ionic liquid stationary phases include single-cationed [22-24], di-cationed [25,26] and multi-cationed [27,28] micro-molecular ILs. They are routinely synthesized via
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quaternization and metathesis [29]. Compared with single-cationed ILs, di-cationed and multi-cationed ILs usually exhibit better thermo-stability.
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The blending ionic liquid stationary phases refer to the mixture of two ionic liquids [30] or of
an ionic liquid and a conventional stationary phase like OV-1701 [31]. Blending is an effective way to acquire a new stationary phase with improved performances, but the durability is not undisputed. The polymeric ionic liquid stationary phases can be further classified into two categories by the location of IL moieties, at the side chains or the main chain. Two approaches have been proposed for the synthesis of the former ones. (1) Polymerization of vinyl ionic liquids. Initiated by AIBN, 2
some vinyl imidazolium [32,33] or phosphonium [34] ILs have been used to synthesize polymeric stationary phases with IL moieties at side chains. (2) Polymer modification. Two synthesis routines have been proposed as follows. One routine [35,36] is that a polysiloxane with side chains of 3-chloropropyl groups is synthesized and then react with 1-methylimidazole via quaternization reaction to form IL moieties at side chains. The obtained stationary phases not only
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inherit the character of "dual nature" from ILs, but also inherit the excellent film-forming ability from polysiloxanes. The other is based on hydrosilylation reaction of hydrogen silicone oil with vinyl ionic liquids [37]. As for polymeric stationary phases with IL moieties at main chains, 1-(3-chlorohexyl) imidazole [12] can be used to produce a polymer through consecutive
quaternization reactions. If N-vinylimidazole is employed to cap the terminal Cl atoms at the
polymeric ionic liquid, this kind of polymer can further polymerize through radical reaction of the vinyl groups.
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ILs are also called "designer solvents" [38], and it is because their properties can be tuned by
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varying the chemical structure of cation or anion moieties. Considering the principle of chromatography, that implies IL modification will bring us a great opportunity to develop some
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stationary phases with special selectivity. In this paper, a convenient and applicable synthesis
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strategy of ionic liquid bonded polysiloxanes (PILs) is proposed as follows: firstly, the polysiloxane with imidazole groups at the side chains is synthesized as a modifying platform; secondly, these imidazole groups further react with various halogenated compounds through
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quaternization to produce a big family of PILs. Upon this approach, we have obtained fifteen PIL
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stationary phases differing in IL content, IL group or combination of different IL groups. After they were used to prepare capillary columns through static coating, the column efficiencies and durability were tested. Then the approach of Rohrschneider-McReynolds constants were used to
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measure their column polarity. It was resulted that the general polarity indexes of the obtained columns fall in the range from 218 to 717. And IL content, structure of the IL and combination of
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different IL groups have noticeable influences on interaction features of the stationary phases. Finally, the PIL stationary phases were tested chromatographically using a series of mixed
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samples including aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. And the separation selectivity of them was compared to that of conventional polar columns TG-17ms and Elite-waxetr. It suggests that upon this synthesis strategy, we can acquire abundant PIL stationary phases with especial separation selectivity. 2. Experimental 2.1 Apparatus and Reagents All the GC analyses were carried out using a FULI 9710 gas chromatograph equipped with 3
flame ionization detector (FULI INSTRUMENTS, China). Nitrogen was used as the carrier gas with a flow rate of 0.4 mL/min for 10 m long columns and 1.0 mL/min for 30 m long columns. The injector and detector temperatures were set at 280 oC, the make-up flow of nitrogen at 30 mL/min, the hydrogen flow at 35 mL/min and the air flow at 350 mL/min. Methane was used as the dead time marker. FI-IR analysis was performed on a Thermo Nicolet 670 instrument (Thermo,
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USA), and 1HNMR analysis on a Mercury VX-300 instrument (300MHz, Varian, USA). Imidazole, sodium hydroxide, sodium iodide, acetone, tetrahydrofuran, potassium hydroxide, thionyl chloride, chloroform, acetonitrile and diethyl ether were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 3-Chloropropylmethyldiethoxysilane were purchased from Jianghan Fine Chemical Co., Ltd. (Jingzhou, China). Lithium
bis(trifluoromethanesulfonylimide) (LiNTf2), dimethyldiethoxysilane (DMDES),
hexamethyldisiloxane (HMDSO), 1-bromooctane, 1-bromododecane, 1-bromooctadecane,
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1-bromo-3-methylbutane, 1-bromo-3-phenylpropane, 3-chloro-1,2-propanediol,
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11-bromo-1-undecanol and 4-bromobutyronitrile were purchased from Aladdin Industrial Corporation (Shanghai, China). Benzene, n-butanol, 2-pentanone, 1-nitropropane, pyridine and all
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of the analytes for the selectivity test were purchased from J&K Scientific Ltd. (Beijing, China).
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3-Chloropropylmethyldiethoxysilane is technical grade and was purified by distillation before use. All the other reagents are analytical grade. 2-(2-(2-(2-Chloroethoxy)ethoxy)ethoxy)ethanol used in this paper was synthesized according to the reference [39]. The bare fused-silica capillary tube
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with a protecting polyimide coating (0.25 mm i.d.) was purchased from Yongnian Optical Fiber
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Factory (Hebei, China). The TG-17ms column (30 m × 0.25 mm i.d., film thickness 0.25 μm) was purchased from Thermo Scientific (USA), and its column efficiency is 2675 plates/m (naphthalene, k = 7.74, 120 oC). The Elite-waxetr column (30 m × 0.25 mm i.d., film thickness 0.25 μm) was
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purchased from PerkinElmer Life and Analytical Sciences (USA), and its column efficiency is 4205 plates/m (naphthalene, k = 6.40, 120 oC).
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2.2 Synthesis of the PILs The synthesis routine of the PILs is showed in Fig. 1. And the detailed supplementary
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information is listed in the Supplementary Material. 2.2.1 Synthesis of Imidazole Bonded Polysiloxanes (PSO-IMs) The synthesis of PSO-IMs roughly comprises two steps, synthesis of N-(3-propylmethyldiethoxysilane)imidazole (C3) and polycondensation of C3 with dimethyldiethoxylsilane (DMDES). After sodium imidazolide (C1) and 3-iodopropylmethyldiethoxysilane (C2) were synthesized according to the references [40] and [41] respectively, C3 was synthesized by the reaction of C1 4
with C2 according the reference [42]. The synthesis procedures of C1, C2 and C3 are presented in the Supplementary Material. General synthesis procedures for PSO-IMs: KOH aqueous solution was added dropwise to a mixture of C3 and DMDES. After stirring at 80 oC for 12 h, the formed ethyl alcohol was removed from the reaction mixture under vacuum. Hexamethyldisiloxane (HMDSO) was added and then,
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the reaction temperature was raised to 105 oC and kept for another 48 h. An oil-water separator was used to remove the ethyl alcohol and water formed during this reaction process. The resultant was dissolved in chloroform (20 mL) and then washed with water till neutrality. After chloroform was removed under reduced pressure, a PSO-IM was obtained as a light yellow viscous liquid.
By changing the ratio of C3 to DMDES, we have synthesized three kinds of polysiloxanes with different imidazole contents termed respectively as PSO-IM(7.8%), PSO-IM(16%) and
PSO-IM(33%). The imidazole content in this paper refers to the percentage of imidazole units in
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total units. The amount of reactants and products is listed in Table 1.
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2.2.2 Synthesis of the PILs
PSO-IMs react with halogenated compounds to form PILs. Different halogenated compounds
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lead to different substituent groups at 3- position of the imidazole ring, namely different IL groups.
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Two sets of PILs have been synthesized in this work. One bears only one type of IL groups and is named as Mono-PIL. The other bears two types of IL groups and is named as Bi-PIL. In this paper, "substituent group" refers to the group at the 3- position of the imidazole ring except especial
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Material), respectively.
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definition. The detailed synthesis information is listed in Table S2 and Table S3 (Supplementary
2.2.2.1 Synthesis of the Mono-PILs General procedure: A certain amount of PSO-IM (e.g. PSO-IM(16%)) and a halogenide (e.g.
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1-bromo-3-methylbutane) were dissolved in dried organic solvent 1 (e.g. chloroform), and the solution was stirred under nitrogen and heated to reflux. 48 h later, solvent 1 was evaporated under
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vacuum. The residue was washed with solvent 2 (e.g. n-hexane) to remove the unreacted halogenide. Then the crude product was dissolved in 3 mL dried solvent 3 (e.g. ethanol) and a
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solution of NTf2Li in dried solvent 3 was added. The mixture was stirred for 24 h at room
temperature. After that, solvent 3 was evaporated under vacuum. The residue was redissolved in chloroform and washed with water until halide ions could not be found by silver nitrate test. At last, chloroform was removed under reduced pressure and a Mono-PIL (e.g. PIL-iC5(16%)) was obtained as a light yellow viscous liquid. 2.2.2.2 Synthesis of the Bi-PILs General procedure: A certain amount of R1X (e.g. 1-bromooctane) and PSO-IM (e.g. 5
PSO-IM(16%)) were added to dried acetonitrile. The mixture was stirred under nitrogen at 80 oC for 48 h. Then, a certain amount of R2X (e.g. 4-bromobutyronitrile) was also added to this reaction solution, and the temperature was kept at 80 oC for another 48 h. Then NTf2Li in dried acetonitrile was added and the mixture was stirred for 24 h at room temperature. After the solvent of acetonitrile was evaporated, solvent 1 (e.g. n-hexane) and solvent 2 (e.g. diethyl ether) were used
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successively to wash away the unreacted R1X and R2X from the residue. After that, the residue was redissolved in chloroform and washed with water until halide ions could not be found by
silver nitrate test. Finally, chloroform was removed under reduced pressure and a Bi-PIL (e.g. PIL-C8&CN) was obtained as a light yellow viscous liquid. 2.3 Preparation of Capillary Columns
Before coating, each bare fused-silica capillary tube (11 m × 0.25 mm i.d.) was rinsed with 20
mL methanol and 20 mL dichloromethane successively. After that, the capillary tubes were purged
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with nitrogen gas, and conditioned from 50 to 260 oC at 2 oC/min and held at 260 oC for 3 h. Then
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the capillary tubes were statically coated using 0.30% (w/v) of stationary phases dissolved in dichloromethane (for PIL-C8(16%), PIL-C12(7.8%), PIL-C12(16%), PIL-C12(33%),
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PIL-C18(16%), PIL-PP(16%), PIL-C8&PP, and PIL-C8&CN) or in methanol (for the other PILs).
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The coated capillary columns were purged with nitrogen gas and conditioned under the following temperature program: 50 oC for 1 h firstly, then increased to 200 oC at 1 oC/min and held for 1 h, and finally increased to the conditioning temperature of each column at 1 oC/min and
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held for 3 h. The obtained columns were cut to about 10 m, sealed with septa at the column ends
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and kept in the desiccator before use. Eq. (1) can be used to approximately calculate the stationary phase film thickness (df) of capillary columns [34,43].
⁄400
(1)
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Where dc is the diameter of the capillary tube (in micrometer), and c is the percentage concentration by weight (w/v, %) of the solution of a stationary phase.
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In this work, dc= 250 μm, and c is set to be 0.30% (w/v), therefore the theoretic film thickness is
about 0.188 μm for each home-made capillary column.
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3. Results and discussion 3.1 1HNMR Characterization 1
HNMR has been used to demonstrate the structures of all synthetic products, including C1～
C3, PSO-IMs and PILs. And all of the data are listed in the Supplementary Material. In the spectrums of PSO-IMs, the ratio of the integral intensity of H at 0.05 ppm (assigned to CH3 on the Si atoms) and that at 7.47 ppm (assigned to C2-H of the imidazole rings) was used to roughly calculate the imidazole content of each PSO-IM. The calculating equation is shown as Eq. 6
(S1) in the Supplementary Material. And the imidazole contents of the three PSO-IMs are 7.8%, 16% and 33%, respectively. For all PILs, the actual contents of IL groups are in accordance to the imidazole contents of the PSO-IMs used approximately, demonstrated by 1HNMR data. So the bracketed percentages of PILs also refer to the ionic liquid contents. For the three Bi-PILs, the ratio of different IL groups
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was deduced from the integral intensity of characteristic H of the substituent groups at the 1- or 3positions of the imidazole rings. The calculating equations are given in the Supplementary
Material as Eq. (S2), Eq. (S3) and Eq. (S4), respectively. And the calculated ratios are 2:1 (C8/PP), 3:1 (CN/PP) and 1:1 (C8/CN), respectively. 3.2 FT-IR
The fifteen PILs have been characterized by FT-IR (Fig. 2, Fig. S2～S4 in the Supplementary Material). These spectra show some features in common because all these PILs comprise of a
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polysiloxane skeleton and some side chains with imidazolium based IL moieties. The band at 1265
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cm-1 demonstrates the presence of Si-C groups, and the bands at 1050 and 803 cm-1 demonstrate that of Si-O-Si in polysiloxanes. The evidences of IL moieties are as follows, bands between 3085
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and 3148 cm-1 are assigned to unsaturated C-H stretching, and band at 1567 cm-1 is assigned to
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skeleton stretching of the imidazole ring. Among the fifteen FT-IR spectra, only those of PIL-iC5(16%), PIL-C8(16%), PIL-C12(7.8%), PIL-C11-OH(16%), PIL-CN(16%), PIL-TG(7.8%) and PIL-TG(16%) show strong and broad bands in the range between 1632 and 1647 cm-1 and the
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range between 3300 and 3500 cm-1, implying the existence of the adsorbed water.
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For the PILs with the same IL group but different IL contents, the FT-IR spectra exhibit some differences, seeing Fig. 2A. With the increase of IL content, the intensity of unsaturated C-H stretching vibration increases, and so do that of saturated C-H stretching vibration (2850～2965
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cm-1, partly attributed to the substituent groups). For the PILs with the same IL content but different IL groups, in most cases, their FT-IR spectra
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look very alike due to the bands overlap of the substituent groups regardless of the differences in
intensity of the saturated C-H stretching, seeing Fig. S2～S4 in the Supplementary Material.
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Additionally, the characteristic absorption peaks for the substituent groups in the Mono-PILs
are also demonstrated in the FT-IR spectra of the corresponding Bi-PILs, seeing Fig. 2B. 3.3 Column efficiency and durability The column efficiency, retention factor and tailing factor were measured at 100 oC using
naphthalene and listed in Table 2. Each column was always operated below its conditioning temperature and has usually experienced no less than 700 injections within a whole evaluation process. 7
Table 2 shows that except PIL-TG(7.8%) and PIL-C3-2OH(16%), most of the columns possess good thermal stability and their conditioning temperatures are not lower than 280 oC. Six alkyl Mono-PILs and three Bi-PILs own the best thermal stability since their conditioning temperatures are up to 300 oC or even higher. As the test of baseline bleeding can reflect the loss of a stationary phase during a practical application, the baselines of the whole PIL columns have been recorded
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within the range from 100 to 400 oC at the rate of 3 oC·min-1 and shown in Fig. S5 (Supplementary Material). As shown in Fig. S5, most of the PIL stationary phases start to bleed after 270 oC.
Among these stationary phases, PIL-C8&PP, PIL-C18(16%) and PIL-C12(33%) start to bleed around 300 oC, and they own the highest thermal stability. On the other hand, most alkyl
Mono-PILs and all Bi-PILs have higher column efficiencies. And their column efficiencies and retention factors change little after a test period of six months. These demonstrate that alkyl Mono-PILs and Bi-PILs have good durability.
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Since all of the stationary phase solutions for static coating have the same concentration, all
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home-made capillary columns have the same film thickness theoretically [44]. Therefore, the retention factors showed in Table 2 primarily reveal the interaction strength between naphthalene
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and the stationary phases differing in IL structure or IL content. When the IL groups are the same,
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the retention factors increase gradually as the IL content increases; when the IL contents are the same and the substituent groups are n-alkyl groups, the retention factors also increase with the increase of carbon numbers of the n-alkyl groups. Moreover, Bi-PILs afford larger retention
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factors than the corresponding Mono-PILs.
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Table 2 also exhibits that the tailing factors of all columns are close to 1 except PIL-PP(16%). This indicates that most films obtained by static coating are uniform. PIL-PP(16%) is quite different from the other stationary phases and its tailing factor is excessively large (1.51 and 1.73).
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This might be attributed to the excessively strong interactions between naphthalene and PIL-PP(16%), which may be explained further by the principle of "like dissolves like".
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3.4 Column polarity
Polarity is generally used to describe the overall capacity of a stationary phase for all possible
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intermolecular interactions [45]. It is commonly characterized by the sum of five Rohrschneider-McReynolds constants, or the arithmetic average of the constants, termed as "general polarity index" (GPI) [46]. This approach was put forward by Rohrschneider in 1966 [47] and improved by McReynolds in 1970 [48]. Such constants as X', Y', Z', U' and S' represent five specific interactions between a stationary phase with the solutes: X'- dispersive interactions; Y'-
proton donor and acceptor capabilities plus dipolar interactions; Z'- dipolar interactions plus weak proton acceptor, but not proton donor capabilities; U'- dipolar interactions; and S'- strong proton 8
acceptor capabilities. Rohrschneider-McReynolds constants and GPI (80 oC) of each PIL have been measured, and the data are exhibited in Table S4 (Supplementary Material). Upon our synthesis strategy, the obtained PILs afford quite different GPIs, ranging from 218 to 717. Both PIL-TG(7.8%) and PIL-C18(16%) have GPIs below 300, PIL-C12(33%), PIL-PP(16%) and three Bi-PILs between 300 and 400, four columns including PIL-C12(16%), PIL-iC5(16%),
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PIL-C3-2OH(16%) and PIL-CN(16%) between 400 and 500, and the other columns including PIL-C8(16%), PIL-C12(7.8%), PIL-TG(16%) and PIL-C11-OH(16%) above 500. As a
comparison, GPI of the conventional medium polar column of TG-17ms was measured to be 189, and that of the conventional strong polar column of Elite-waxetr 463 (also seeing Table S4).
Furthermore, these stationary phases offer quite different interaction features. PIL-C11-OH(16%) owns the largest Y' (930), Z' (906) and S' (1097), and PIL-TG(16%) and PIL-iC5(16%) offer the
largest X' (331) and U' (717), respectively. PIL-TG(7.8%) has the smallest X' (88), U' (228) and S'
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(200), and PIL-C18(16%) shows the smallest Y' (258) and Z' (235). When line diagrams were
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made using these data, we found some interesting relations between the chemical structures of the PILs and their interaction features or GPIs, seeing Fig. 3～5.
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Fig. 3 exhibits that if the substituent groups are non-polar groups like n-dodecyl, GPI decreases
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with the increase of IL content. But if the substituent groups are polar groups like tetraglycol, GPI increases with the increase of IL content. On the other hand, if the substituent groups are non-polar groups, Y' and Z' decrease with the increase of IL content, but if the substituent groups
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are polar groups, Y' and Z' increase with the increase of IL content. No matter the substituent
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groups are non-polar or polar, both U' and X' increase with the increase of IL content. These results imply that both the IL content and the polarity of the substituent groups are important factors to tune GPIs or interaction features of the PILs.
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Fig. 4 shows that, when the substituent groups are normal-alkyl groups (e.g. n-octyl, n-dodecyl or n-octadecyl), the reduction in the carbon numbers of n-alkyl groups leads to the increased GPIs
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or interaction features of the PILs. But when the substituent groups are isomerized alkyl groups (e.g. iso-pentyl), you will find an interesting result. Though the carbon number of iso-pentyl is less
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than that of n-octyl, PIL-iC5(16%) does not have a larger GPI than PIL-C8(16%) due to the
unexpected reduction in Y', Z' and S'. That means the configuration of a substituent group also has important effect on the GPIs or interaction features of the PILs. It had been supposed that the GPIs of the Bi-PILs would lie in between that of the corresponding Mono-PILs. In fact, some experimental results are unexpected. Fig. 5A～5C show that integrating two different IL groups into one stationary phase brings great changes to the GPIs of the Bi-PILs and some of their interaction features. The GPIs of most Bi-PILs are smaller than 9
that of the corresponding Mono-PILs. Among the five interaction features, U' and X' of the Bi-PILs are similar to that of the corresponding Mono-PILs. All Bi-PILs have much smaller S' than their corresponding Mono-PILs. As for Y' and Z', the Bi-PILs roughly lie in between the corresponding Mono-PILs. 3.5 Separation performances of the PIL stationary phases
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3.5.1 Aliphatic esters Fig. 6A～6D show the chromatograms of ten aliphatic esters on PIL-TG(7.8%), PIL-C8(16%) and two conventional polar columns (TG-17ms and Elite-waxetr). These aliphatic esters can be
categorized into three groups of isomers. Group 1: ethyl propionate and propyl acetate; group 2:
ethyl butyrate, isobutyl acetate and propyl propionate; group 3: the rest aliphatic esters tested. On the TG-17ms (GPI: 189) and Elite-waxetr (GPI: 463), there was a pair of co-eluting isomers
respectively. But on PIL-TG(7.8%) whose GPI is 218, between that of TG-17ms and Elite-waxetr,
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all of the aliphatic esters could be baseline separated. So we think the GPI of a stationary phase is
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not good enough to represent the separation selectivity towards aliphatic esters. In order to reveal the features based on a stationary phase’s characteristic interactions more exactly, herein we
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proposed an index termed as "contribution rate" (CR). It is derived from the rate of each polarity
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constant to the sum of five polarity constants of a stationary phase. Every stationary phase has five CRs. For example, CRX' = X'/(X'+Y'+Z'+U'+S'). Then, the selectivity of a stationary phase can be described by five indexes of CRi (i=X', Y', Z', U' or S'). Fig. 6E is the diagram of CR indexes of
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the four stationary phases mentioned above. Although there is a great difference between
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TG-17ms and Elite-waxetr in GPI, Fig. 6E clearly shows the two stationary phases are so similar, having four similar CR indexes except CRY'. This result may account for the similar drawback of these two stationary phases in the isomer separation, each having a pair of unresolved isomers. On
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the other hand, PIL-TG(7.8%) shows quite different CR indexes from that of TG-17ms and Elite-waxetr (Fig. 6E), and offers different or better separation ability to the isomers (Fig. 6A).
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Therefore, we think that CR index can be used to differentiate the separation performances of stationary phases.
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In fact, Fig. 6E not only reveals the great distinctions between the conventional stationary
phases and PIL ones on CR indexes, but also that between the two PIL stationary phases. Firstly, both PIL stationary phases have CRX' indexes below 10%, while the CRX' indexes of the two
conventional stationary phases are about 15%. Since dispersive interaction is not a key role in isomer separation, in our opinion, decreasing CRX' naturally leads to increased other CR indexes related to proton donor and acceptor capabilities and dipolar interactions. This may at least be part of the reason why both PIL stationary phases have better selectivity towards the tested isomers. 10
Secondly, for the two PIL stationary phases, there are also significant differences in CR indexes. PIL-C8(16%) has much larger CRS', but smaller CRU' and CRZ' than PIL-TG(7.8%). These differences are reflected on the selectivity of the stationary phases necessarily. The elution orders of two pairs of isomers (ethyl butyrate/ isobutyl acetate, isoamyl acetate/ propyl butyrate) are reverse on PIL-TG(7.8%) and PIL-C8(16%). In other words, PIL-C8(16%) can retain the ester of
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iso-alcohol stronger than retain that of n-alcohol, and PIL-TG(7.8%) does inversely. 3.5.2 Dichloro-anilines
Fig. 7A～7D show the chromatograms of six dichloroaniline isomers on PIL-C11-OH(16%), PIL-TG(16%) and two conventional polar columns (TG-17ms and Elite-waxetr), and Fig. 7E exhibits the diagram of CR indexes of these four stationary phases.
The tested dichloro-anilines could be separated well on the four columns, but considering the
short column lengths of the two PIL columns, it is reasonable to say that the PIL stationary phases
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offer better separation efficiency than TG-17ms and Elite-waxetr. Moreover, it is interesting the
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elution order of 2,4-dichloroaniline and 2,5-dichloroaniline on PIL-C11-OH(16%) is different from that on the other three stationary phases. As shown in Fig. 7E, except for CRY', the other four
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CR indexes of PIL-C11-OH(16%) are different from those of the other stationary phases.
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PIL-C11-OH(16%) affords much bigger CRZ' and CRS' than the other stationary phases. While Z' represents the dipolar interactions plus weak proton acceptor, but not proton donor capabilities, and S' represents the strong proton acceptor capabilities. On the other hand, since the predicted
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pKa of 2,4-dichloroaniline and 2,5-dichloroaniline are 2.02 ± 0.10 and 1.60 ± 0.10 respectively
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(SciFinder, https://scifinder.cas.org/scifinder/view/scifinder/scifinderExplore.jsf), 2,4-dichloroaniline should be a relatively stronger basic than 2,5-dichloroaniline and also a relatively stronger proton acceptor. Moreover, the CRS' and CRZ' of PIL-C11-OH(16%) are very
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salient, so it is not difficult to understand why 2,4-dichloroaniline was eluted after 2,5-dichloroaniline on PIL-C11-OH(16%).
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3.5.3 Alcohols
It was reported alcohols frequently formed tailing peaks on ionic liquid stationary phases, such
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as imidazolium-based [49] and phosphonium-based [24] ionic liquids, and polymeric imidazolium ionic liquids [50]. As shown in Fig. 8A, alcohols do show severe tailing peaks on PIL-iC5(16%), and iso-octanol is co-eluted with n-heptanol on this column. But on the PIL-C12(7.8%), PIL-TG(7.8%) and PIL-C18(16%), the alcohols are separated well and give symmetrical peaks, seeing Fig. 8B～8D. In addition to the improved coating performances, this may also be related to the unique interaction characteristics. 3.5.4 Other mixed samples 11
Besides the analytes mentioned above, some mixtures of aromatic amines, substituted alkanes, phthalic acid esters, nonane and its isomers, polycyclic aromatic hydrocarbons and n-alkanes have also been tested on the home-made PIL columns, seeing Fig. 9. The baseline separations are achieved for all of the analytes except for anthracene and phenanthrene (Fig. 9E). In summary, upon the synthesis strategy mentioned above, we can not only obtain the PIL
SC RI PT
stationary phases similar to the conventional polar stationary phases, but also acquire the PIL stationary phases with special separation selectivity. 4. Conclusions
In this paper, we put forward a novel synthesis strategy for PILs. Based on the synthesized
imidazole bonded polysiloxanes, abundant and readily available organic halogenides can be used to synthesize various PILs. Through this synthesis strategy, we have synthesized fifteen PILs
differing in IL content, IL group, or combination of different IL groups. Their GPIs fall in a broad
U
range from 218 to 717. And the GPI and interaction features can be tuned by changing IL contents,
N
chemical structures of IL groups and combinations of different IL groups. It was also resulted that most alkyl Mono-PILs and Bi-PILs own better thermal stability and durability. Moreover, different
A
interaction characteristics of the different PIL stationary phases lead to their different separation
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selectivity for a variety of analytes including aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. So this synthesis strategy is beneficial to the development of polar stationary phases with good thermal stability and unique separation selectivity, and to
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D
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SC RI PT
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trennflüssigkeiten, J. Chromatogr. A 22 (1966) 6-22. [48] W.O. McReynolds, Characterization of some liquid phases, J. Chromatogr. Sci. 8 (1970) 685-691.
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ionic liquids as valuable stationary phases in gas chromatography: Chemical synthesis and full
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Figure captions: Fig. 1. Synthesis routine of the PILs. Reagents: (i) NaOH; (ii) NaI; (iii) THF; (iv) DMDES,
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A
N
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SC RI PT
HMDSO, KOH, H2O; (v) R1-X; (vi) R2-X; (vii) NTf2Li.
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Fig. 2. FT-IR spectra of PILs. (A) FT-IR spectra of PIL-C12(7.8%), PIL-C12(16%) and
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CC
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PIL-C12(33%). (B) FT-IR spectra of PIL-C8(16%), PIL-CN(16%) and PIL-C8&CN.
17
SC RI PT
Fig. 3. Diagram of Rohrschneider-McReynolds constants and GPIs against the IL contents. The
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D
M
A
N
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substituent groups are (A) n-dodecyl groups and (B) tetraglycol groups, respectively.
Fig. 4. Diagram of Rohrschneider-McReynolds constants and GPIs against the carbon numbers of
A
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the alkyl substituent groups.
18
Fig. 5. Diagram of Rohrschneider-McReynolds constants and GPIs of the Bi-PILs and the
D
M
A
N
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SC RI PT
corresponding Mono-PILs. CX(%) refers to the proportion of X in the total units.
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Fig. 6. Chromatograms of aliphatic esters on (A) PIL-TG(7.8%), (B) PIL-C8(16%), (C) TG-17ms and (D) Elite-waxetr, and (E) diagram of CR indexes of these four columns. Peaks: 1. ethyl
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propionate; 2. propyl acetate; 3. isobutyl acetate; 4. ethyl butyrate; 5. propyl propionate; 6. isoamyl acetate; 7. propyl butyrate; 8. ethyl valerate; 9. butyl propionate; 10. n-amyl acetate. Temperature program for (A) and (D): 40 oC for 3 min, 10 oC·min-1 to 100 oC; for (B): 40 oC for 2
A
CC
min, 5 oC·min-1 to 100 oC; for (C): 40 oC for 3 min, 4 oC·min-1 to 100 oC.
19
SC RI PT U N A M D
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Fig. 7. Chromatograms of dichloro-anilines on (A) PIL-C11-OH(16%), (B) PIL-TG(16%), (C) TG-17ms and (D) Elite-waxetr columns, and (E) diagram of CR indexes of these four stationary phases. Peaks: 1. 2,6-dichloroaniline; 2. 2,5-dichloroaniline; 3. 2,4-dichloroaniline; 4.
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2,3-dichloroaniline; 5. 3,5-dichloroaniline; 6. 3,4-dichloroaniline. Temperature program for (A),
A
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(B) and (C): 10 oC·min-1 from 140 oC to 250 oC; for (D): 10 oC·min-1 from 140 oC to 220 oC.
20
SC RI PT
Fig. 8. Chromatograms of alcohols on (A) PIL-iC5(16%), (B) PIL-C18(16%), (C) PIL-C12(7.8%) and (D) PIL-TG(7.8%). Peaks: 1. iso-propanol; 2. n-propanol; 3. iso-butanol; 4. n-butanol; 5.
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iso-pentanol; 6. n-pentanol; 7. n-hexanol; 8. cyclohexanol; 9. n-heptanol; 10. iso-octanol; 11.
n-octanol; 12. n-decanol; 13. n-undecanol; 14. n-dodecanol. Temperature program for (A) and (B):
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60 oC for 1.5 min, 30 oC·min-1 to 260 oC; for (C): 60 oC for 1.5 min, 30 oC·min-1 to 250 oC; for (D):
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A
60 oC for 1.5 min, 30 oC·min-1 to 240 oC.
A
Fig. 9. (A) Chromatogram of the aromatic amines on PIL-CN&PP. Peaks: 1. N,N-dimethylaniline;
2. aniline; 3. o-toluidine; 4. o-chloroaniline; 5. 2,4-dimethylaniline; 6. 3,5-dichloroaniline; 7. 3,4-dichloroaniline; 8. diphenylamine; 9. o-nitroaniline; 10. 1-naphthylamine; 11. toluene-2,4-diamine; 12. m-nitroaniline; 13. p-nitroaniline. Temperature program: 120 oC for 1.5 min, 30 oC·min-1 to 230 oC. (B) Chromatogram of substituted alkanes on PIL-C8&CN. Peaks: 1. 1-bromobutane; 2. acetonitrile; 3. 1-bromine-3-methylbutane; 4. 1-chlorohexane; 5. 1-nitropropane; 6. 21
1-bromooctane; 7. 3-bromopropionitrile; 8. 4-bromobutyronitrile; 9. 1-bromo-3-phenylpropane; 10. 1-bromododecane. Temperature program: 40 oC for 2 min, 30 oC·min-1 to 260 oC. (C) Chromatogram of phthalic acid esters on PIL-TG(7.8%). Peaks: 1. dimethyl phthalate; 2. diethyl phthalate; 3. diisobutyl phthalate; 4. dibutyl phthalate; 5. bis(4-methyl-2-pentyl) phthalate; 6. diamyl phthalate; 7. bis(2-methoxyethyl) phthalate; 8. bis(2-ethoxyethyl) phthalate; 9. dihexyl
SC RI PT
phthalate; 10. bis(2-ethylhexyl) phthalate; 11. butylbenzyl phthalate; 12. bis(2-butoxyethyl) phthalate; 13. dicyclohexyl phthalate; 14. dioctyl phthalate; 15. dinonyl phthalate. Temperature program: 100 oC for 2 min, 20 oC·min-1 to 240 oC.
(D) Chromatogram of n-nonane and its isomers on PIL-C18(16%). Peaks: 1.
2,2,4,4-tetramethylpentane; 2. 2,2,4-trimethylhexane; 3. 3,3-dimethylheptane; 4.
2,3-dimethylheptane; 5. 4-ethylheptane; 6. n-nonane. Temperature program: 40 oC.
(E) Chromatogram of polycyclic aromatic hydrocarbons on PIL-C8&PP. Peaks: 1. naphthalene; 2.
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anthrene; 3. acenaphthene; 4. fluorene; 5. phenanthrene; 6. anthracene; 7. fluoranthene; 8. pyrene;
N
9. benzo(a)anthracene; 10. chrysene; 11. benzo(b)fluoranthene; 12. benzo(k)fluoranthene; 13. benzo(a)pyrene; 14. indeno(1,2,3-cd)pyrene; 15. dibenzo(a,h)anthracene; 16. benzo(g,h,i)perylene.
A
Temperature program: 40 oC for 1 min, 20 oC·min-1 to 150 oC, and then 10 oC·min-1 to 280 oC.
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(F) Chromatogram of 18 n-alkanes on PIL-C12(33%). Temperature program: 120 oC for 1 min,30 C·min-1 to 250 oC.
A
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o
22
Tables: Table 1. Reactant and product information of PSO-IMs with different imidazole contents.
Product
PSO-IM(16%)
PSO-IM(33%)
C3 (g/mol)
2.42 / 0.010
2.42 / 0.010
2.42 / 0.010
DMDES (g/mol)
20.57 / 0.139
9.57 / 0.065
5.79 / 0.039
KOH (g)
0.97
0.46
H2O (mL)
15.5
6.5
0.46
HMDSO (g/mol)
0.12 / 0.00075
0.06 / 0.00038
0.038 / 0.00024
Mass (g)
7.18
3.37
2.56
Yield (%)
60
52
4.5
56
Table 2. Retention factors, tailing factors and column efficiencies. Conditioning
Tailing factor (Tf) a
Retention factor (k)
temperature (oC)
Initial
Six months later
PIL-iC5(16%)
300
3.83
3.70
PIL-C8(16%)
300
4.13
4.13
PIL-C12(7.8%)
300
3.66
3.25
PIL-C12(16%)
300
4.11
PIL-C12(33%)
310
7.22
PIL-C18(16%)
300
PIL-TG(7.8%)
250
(plates/m)
Six months later
0.99
0.98
3809
3609
0.97
1.09
3165
3175
0.98
0.96
3892
3643
3.91
0.97
0.95
2962
2606
7.12
1.16
1.10
3873
3614
6.32
6.27
0.98
0.97
3838
3916
3.13
3.06
0.99
0.95
3591
2583
280
4.23
3.12
1.01
1.24
2677
2413
280
2.90
2.79
1.51
1.73
3007
2776
D
M
A
N
Initial
EP
PIL-PP(16%)
Initial
Column efficiency
Six months later
TE
PIL-TG(16%)
U
Stationary phase
SC RI PT
Reactant
PSO-IM(7.8%)
230
3.26
3.18
1.06
1.05
2544
2597
PIL-C11-OH(16%)
280
3.16
3.41
0.99
1.04
2909
2643
PIL-CN(16%)
280
3.62
3.57
1.01
1.07
3037
2895
PIL-C8&PP
300
6.65
6.54
0.97
0.99
3612
3720
PIL-CN&PP
300
4.48
4.39
0.96
0.95
3321
3527
A
CC
PIL-C3-2OH(16%)
PIL-C8&CN 300 5.78 5.87 0.99 1.04 4000 4047 a T f W 0.05 2 f , in this formula, W0.05 is the peak width at 5% height, and f is the front half-width measured from the leading edge to a perpendicular dropped from the peak apex. A tailing factor of 1 means a symmetric peak.
23