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Separation performance of graphene oxide as stationary phase for capillary gas chromatography
Chinese Chemical Letters 26 (2015) 47–49
Contents lists available at ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Separation performance of graphene oxide as stationary phase for capillary gas chromatography Yu Feng, Chuan-Gang Hu, Mei-Ling Qi *, Ruo-Nong Fu, Liang-Ti Qu * Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials and School of Chemistry, Beijing Institute of Technology, Beijing 100081, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 August 2014 Received in revised form 6 September 2014 Accepted 24 September 2014 Available online 14 October 2014
Graphene oxide (GO) has attracted extensive attention due to its unique properties and potential applications. Here, we report the investigation of GO nanosheets as a stationary phase for capillary gas chromatographic (GC) separations. The GO column, fabricated by a new one-step coating approach, showed average McReynolds constants of 308, suggesting the medium polar nature of the GC stationary phase. The GO stationary phase achieves good separation for analytes of different types with good peak shapes, especially for H-bonding analytes, such as alcohols and amines. The different retention behaviors of GO stationary phase from the conventional stationary phase may originate from its multiple interactions with analytes, involving H-bonding, dipole–dipole, p–p stacking and dispersive interactions. Moreover, GO column showed good separation reproducibility with relative standard deviation (RSD%) less than 0.24% (n = 5) on retention times of analytes. ß 2014 Mei-Ling Qi. Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. All rights reserved.
Keywords: Graphene oxide nanosheets Stationary phase Separation performance Capillary gas chromatography
1. Introduction Graphene oxide (GO) is a single-layered nanosheet with epoxy, hydroxyl and carboxyl groups on the basal plane and edges of graphitic backbone [1–3], offering high surface area and abundant interaction sites with analytes. It has received tremendous attention [4,5] due to its novel physicochemical properties. Like other nanomaterials used in separation science [6], GO has been reported as a separation material in capillary electrochromatography [7–11] and capillary gas chromatography (GC) [12]. Qu and coworkers reported the use of GO as GC stationary phase, proving its potential for this purpose, although severe peak tailing was observed for alcohols [12]. In fact, there is great difficulty in preparing a GO capillary column with satisfactory efficiency since GO nanosheets tend to aggregate in dichloromethane used in GC column preparation. To address the problem, 3-aminopropyldiethoxymethylsilane (3-AMDS) [11,12] was used as a coupling agent for covalently bonding with GO in two steps, first, coating 3AMDS onto the capillary and then coating GC nanosheets onto it. Herein, we report a one-step column coating approach for fabrication of GO capillary column for GC separations. This
* Corresponding authors. E-mail addresses: [email protected] (M.-L. Qi), [email protected] (L.-T. Qu).
proposed coating approach combines the two steps into one and makes the coating process more feasible and efficient and achieves an improved separation performance, showing advantages over the reported column coating method [12]. In this work, the GO capillary column was evaluated in terms of column efficiency, McReynolds constants, separation performance and reproducibility. 2. Experimental 2.1. Chemicals and instruments All the analytes in this work were of analytical grade. GO was prepared following the modified Hummers method [13–15]. Untreated fused-silica capillary tubing (0.25 mm i.d.) was purchased from Yongnian Ruifeng Chromatogram Apparatus Company (Hebei, China). A commercial HP-INNOWAX capillary column purchased from Agilent Technologies (5 m long 0.25 mm i.d.) was also used for comparison. All the GC separations were carried out on a GC 7890A gas chromatograph with a flame ionization detector (FID) (Agilent Technologies, USA) under the following GC conditions: nitrogen of high purity (99.999%) as carrier gas at a flow rate of 1 mL/min, injection port at 250 8C and FID at 300 8C. Temperature programs for the separations of different samples are individually provided in their figure captions.
http://dx.doi.org/10.1016/j.cclet.2014.10.001 1001-8417/ß 2014 Mei-Ling Qi. Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. All rights reserved.
Y. Feng et al. / Chinese Chemical Letters 26 (2015) 47–49
48
comparable Y0 value (H-bond donor and acceptor) to that of the conventional Wax phase and lower S0 (H-bond acceptor) and Z0 (dipole–dipole interaction) values than the latter, suggesting that H-bonding and dipole–dipole interactions may play a major role in the retention of the GO stationary phase for analytes of different types.
Table 1 McReynolds constants of GO and HP-INNOWAX capillary columns. Column
X0
Y0
Z0
U0
S0
Sum
Average
GO HP-INNOWAX
127 322
517 536
230 368
374 572
293 510
1541 2308
308 462
X0 : benzene; Y0 : 1-butanol; Z0 : 2-pentanone; U0 : 1-nitropropane; S0 : pyridine.
3.2. Separation performance 2.2. Capillary column fabrication Separation performance of the GO capillary column was evaluated by GC separations of analytes of different functionalities, including n-alkanes, aromatic hydrocarbons, alcohols, amines and a mixture of 11 analytes. The corresponding GC separation chromatograms are shown in Figs. 1–3, respectively. Fig. 1 describes the GC separations of n-alkanes (a), aromatic hydrocarbons (b) and alcohols (c) on the GO column, respectively, showing the good separation performance of GO stationary phase for analytes from non-polar to polar. Especially, the GO stationary phase exhibited good peak shapes for alcohols that are known to be prone to peak tailing in GC analysis due to their strong H-bonding tendencies with a polar stationary phase. This suggests moderate interactions with alcohols as well as good column inertness. Based on this finding, we proceeded to further investigate the separation performance of GO capillary column for other H-bonding analytes, such as amines. Fig. 2 shows the GC separations of amines on GO (a) and conventional Wax (b) capillary columns, respectively. Amines are proton-acceptor and liable to peak tailing in GC analysis. As can be observed, the GO column exhibited good peak shapes, especially for di-n-hexylamine (peak 2) and dodecylamine (peak 3). Dodecylamine had a shortened peak height on the commercial column, suggesting the possible existence of active sites on the indicated column. The above results demonstrated the good separation performance of the GO stationary phase for H-bonding analytes, such as alcohols and amines. Fig. 3 presents the GC separations of a mixture of 11 analytes on GO (a) and conventional Wax (b) capillary columns. As shown, the GO stationary phase achieved baseline resolution for all the analytes and exhibited different retention behaviors for some of the analytes from the conventional Wax phase. Specifically, the GO stationary phase completely resolved chlorobenzene (peak 2) and n-dodecane (peak 4), which were partially separated on the conventional phase (R = 0.66). Of particular note, the nonpolar analytes, such as n-dodecane (peak 4) and methyl nonanoate (peak 7) are retained longer on the GO column, which eluted earlier on the Wax column and resulted in the switched elution order of
The capillary column coated with GO was fabricated as follows. First, a bare capillary column (5 m 0.25 mm) was rinsed with dichloromethane for 10 min, heated at 100 8C for 10 min, washed with 1.0 mol/L sodium hydroxide for 1.5 h and then with water until the eluate was neutral. After this, the column was heated at 120 8C for 2.0 h. Then, a GO dispersion was prepared by dispersing 200 mL GO aqueous solution (1 mg/mL) in a mixture of 100 mL 3AMDS and 500 mL ethanol under ultrasonication for 10 min. Next, the capillary was filled with the GO dispersion and maintained at room temperature for 1.0 h with both ends sealed. Afterwards, it was conditioned from 40 8C to 170 8C at 1 8C/min and held at the high-end temperature for 5 h under nitrogen flow. Finally, the capillary column coated with GO nanosheets was obtained and used for the following GC separations.
3. Results and discussion 3.1. McReynolds constants and column efficiency Column efficiency of the GO column was determined with naphthalene at 120 8C. The determined height equivalent to a theoretical plate (HETP) was 0.74 mm, corresponding to the column efficiency of 1350 plates/m. McReynolds constants are an empirical measure of the polarity of a GC stationary phase for the characterization of the possible interactions of a stationary phase with analytes. They can be experimentally measured by determining the differences of five probes, namely benzene (X0 ), 1-butanol (Y0 ), 2-pentanone (Z0 ), 1-nitropropane (U0 ) and pyridine (S0 ), in the retention indices on the given stationary phase and squalane. The sum and average of the retention index differences (DI) for the five probes correspond to a measure of the overall polarity and average polarity of a GC stationary phase, respectively. Table 1 shows the resulting McReynolds constants (DI) and their sum and average values of the GO capillary column, suggesting its moderately polar nature. As shown, it exhibits 1
(a)
500
3
4
5
500
8 4
300 pA
pA
200
7
6
150
200
5
50 0
2
4
6
Time (min)
8
10
0
5 2
300
7 6
8 10
3 9
200
3
100
4
400
1
100
0
(c)
600
2
400
2
250
1
700
(b)
300
pA
350
100
0
5
10 Time (min)
15
20
0
0
2
4
6 8 Time (min)
10
12
14
Fig. 1. GC separations of n-alkanes (a) aromatic hydrocarbons (b) and alcohols (c) on GO capillary column. Peaks for (a): (1) n-nonane, (2) n-decane, (3) n-undecane, (4) ndodecane, (5) n-tridecane; (6) n-tetradecane, (7) n-pentadecane and (8) n-hexadecane; for (b): (1) naphthalene, (2) biphenyl, (3) fluorene, (4) phenanthrene and (5) fluoranthene; for (c): (1) 1-propanol, (2) 1-butanol, (3) 1-pentanol, (4) 1-hexanol, (5) 1-heptanol, (6) 1-octanol, (7) 1-nonanol, (8) 1-decanol, (9) 1-undecanol and (10) 1dodecanol. Temperature programs: (a) 40 8C (1 min) to 130 8C at 10 8C/min, (b) 40 8C (1 min) to 160 8C at 10 8C/min and (c) 40 8C (1 min) to 140 8C at 10 8C/min.
Y. Feng et al. / Chinese Chemical Letters 26 (2015) 47–49
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Fig. 2. GC separations of amines on GO (a) and HP-INNOWAX (b) capillary columns. Peaks: (1) dimethylformamide, (2) di-n-hexylamine, (3) dodecylamine, (4) di-noctylamine. Temperature programs: (a) 40 8C (1 min) to 150 8C at 10 8C/min and (b) 40 8C (1 min) to 200 8C at 10 8C/min.
Fig. 3. GC separations of a mixture of 11 analytes on GO (a) and HP-INNOWAX (b) capillary columns. Peaks: (1) toluene, (2) chlorobenzene, (3) bromobenzene, (4) n-dodecane, (5) 1,2-dichlorobenzene, (6) benzonitrile, (7) methyl nonanoate, (8) naphthalene, (9) aniline, (10) 3-toluidine and (11) biphenyl. Temperature program: 30 8C (1 min) to 140 8C at 10 8C/min.
bromobenzene/n-dodecane (peaks 3/4) and 1,2-dichlorobenzene/ benzonitrile (peaks 5/6), demonstrating their different separation performance and retention behaviors. Additionally, separation reproducibility of GO column in retention times of analytes was examined by separation of the mixture of 11 analytes. The obtained relative standard deviations (RSD%) were in the range of 0.03%–0.24% (n = 5), indicating the good reproducibility of GO column for the GC separations. 4. Conclusion This work describes the separation performance of GO nanosheets as a capillary GC stationary phase. The GO column fabricated by a new single-step coating approach exhibited different resolving ability from the conventional Wax column and achieved good peak shapes for H-bonding analytes, such as alcohols and amines that are prone to peak-tailing in GC analysis. These differences may originate from their different molecular interactions. The GO stationary phase exhibits moderate H-bonding and dipole–dipole interactions with H-bonding analytes and offers stronger p–p interactions with aromatic analytes than the latter. The comprehensive result of these molecular interactions distinguishes the GO stationary phase from the conventional stationary phase in term of retention behaviors and resolving ability. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 21075010, 21174019) and the 111 Project B07012 in China.
References [1] D.R. Dreyer, S. Park, C.W. Bielawski, R.S. Ruoff, The chemistry of graphene oxide, Chem. Soc. Rev. 39 (2010) 228–240. [2] Y. Zhu, S. Murali, W. Cai, et al., Graphene and graphene oxide: synthesis, properties and applications, Adv. Mater. 22 (2010) 3906–3924. [3] J.I. Paredes, S. Villar-Rodil, A. Martı´nez-Alonso, J.M.D. Tasco´n, Graphene oxide dispersions in organic solvents, Langmuir 24 (2008) 10560–10564. [4] J. Kim, L.J. Cote, J.X. Huang, Two dimensional soft material: new faces of graphene oxide, Acc. Chem. Res. 45 (2012) 1356–1364. [5] C. Chung, Y.K. Kim, D. Shin, et al., Biomedical applications of graphene and graphene oxide, Acc. Chem. Res. 46 (2013) 2211–2224. [6] E. Guihen, Nanoparticles in modern separation science, Trends Anal. Chem. 46 (2013) 1–14. [7] X. Liu, X.L. Liu, M. Li, L.P. Guo, L. Yang, Application of graphene as the stationary phase for open-tubular capillary electrochromatography, J. Chromatogr. A 1277 (2013) 93–97. [8] Q.S. Qu, C.H. Gu, Z.L. Gu, et al., Layer-by-layer assembly of polyelectrolyte and graphene oxide for open-tubular capillary electrochromatography, J. Chromatogr. A 1282 (2013) 95–101. [9] Y.Y. Xu, X.Y. Niu, Y.L. Dong, et al., Preparation and characterization of open-tubular capillary column modified with graphene oxide nanosheets for the separation of small organic molecules, J. Chromatogr. A 1284 (2013) 180–187. [10] M.M. Wang, X.P. Yan, Fabrication of graphene oxide nanosheets incorporated monolithic column via one-step room temperature polymerization for capillary electrochromatography, Anal. Chem. 84 (2012) 39–44. [11] Q.S. Qu, C.H. Gu, X.Y. Hu, Capillary coated with graphene and graphene oxide sheets as stationary phase for capillary electrochromatography and capillary liquid chromatography, Anal. Chem. 84 (2012) 8880–8890. [12] Q.S. Qu, Y.Q. Shen, C.H. Gu, et al., Capillary column coated with graphene oxide as stationary phase for gas chromatography, Anal. Chim. Acta 757 (2012) 83–87. [13] C.G. Hu, H.H. Cheng, Y. Zhao, et al., Newly designed complex ternary Pt/PdCu nanoboxes anchored on three-dimensional graphene framework for highly efficient ethanol oxidation, Adv. Mater. 24 (2012) 5493–5498. [14] L.J. Cote, F. Kim, J.X. Huang, Langmuir–Blodgett assembly of graphite oxide single layers, J. Am. Chem. Soc. 131 (2009) 1043–1049. [15] W.S. Hummers, R.E. Offeman, Preparation of graphitic oxide, J. Am. Chem. Soc. 80 (1958) 1339.
Contents lists available at ScienceDirect
Chinese Chemical Letters journal homepage: www.elsevier.com/locate/cclet
Original article
Separation performance of graphene oxide as stationary phase for capillary gas chromatography Yu Feng, Chuan-Gang Hu, Mei-Ling Qi *, Ruo-Nong Fu, Liang-Ti Qu * Key Laboratory of Cluster Science, Ministry of Education of China, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials and School of Chemistry, Beijing Institute of Technology, Beijing 100081, China
A R T I C L E I N F O
A B S T R A C T
Article history: Received 1 August 2014 Received in revised form 6 September 2014 Accepted 24 September 2014 Available online 14 October 2014
Graphene oxide (GO) has attracted extensive attention due to its unique properties and potential applications. Here, we report the investigation of GO nanosheets as a stationary phase for capillary gas chromatographic (GC) separations. The GO column, fabricated by a new one-step coating approach, showed average McReynolds constants of 308, suggesting the medium polar nature of the GC stationary phase. The GO stationary phase achieves good separation for analytes of different types with good peak shapes, especially for H-bonding analytes, such as alcohols and amines. The different retention behaviors of GO stationary phase from the conventional stationary phase may originate from its multiple interactions with analytes, involving H-bonding, dipole–dipole, p–p stacking and dispersive interactions. Moreover, GO column showed good separation reproducibility with relative standard deviation (RSD%) less than 0.24% (n = 5) on retention times of analytes. ß 2014 Mei-Ling Qi. Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. All rights reserved.
Keywords: Graphene oxide nanosheets Stationary phase Separation performance Capillary gas chromatography
1. Introduction Graphene oxide (GO) is a single-layered nanosheet with epoxy, hydroxyl and carboxyl groups on the basal plane and edges of graphitic backbone [1–3], offering high surface area and abundant interaction sites with analytes. It has received tremendous attention [4,5] due to its novel physicochemical properties. Like other nanomaterials used in separation science [6], GO has been reported as a separation material in capillary electrochromatography [7–11] and capillary gas chromatography (GC) [12]. Qu and coworkers reported the use of GO as GC stationary phase, proving its potential for this purpose, although severe peak tailing was observed for alcohols [12]. In fact, there is great difficulty in preparing a GO capillary column with satisfactory efficiency since GO nanosheets tend to aggregate in dichloromethane used in GC column preparation. To address the problem, 3-aminopropyldiethoxymethylsilane (3-AMDS) [11,12] was used as a coupling agent for covalently bonding with GO in two steps, first, coating 3AMDS onto the capillary and then coating GC nanosheets onto it. Herein, we report a one-step column coating approach for fabrication of GO capillary column for GC separations. This
* Corresponding authors. E-mail addresses: [email protected] (M.-L. Qi), [email protected] (L.-T. Qu).
proposed coating approach combines the two steps into one and makes the coating process more feasible and efficient and achieves an improved separation performance, showing advantages over the reported column coating method [12]. In this work, the GO capillary column was evaluated in terms of column efficiency, McReynolds constants, separation performance and reproducibility. 2. Experimental 2.1. Chemicals and instruments All the analytes in this work were of analytical grade. GO was prepared following the modified Hummers method [13–15]. Untreated fused-silica capillary tubing (0.25 mm i.d.) was purchased from Yongnian Ruifeng Chromatogram Apparatus Company (Hebei, China). A commercial HP-INNOWAX capillary column purchased from Agilent Technologies (5 m long 0.25 mm i.d.) was also used for comparison. All the GC separations were carried out on a GC 7890A gas chromatograph with a flame ionization detector (FID) (Agilent Technologies, USA) under the following GC conditions: nitrogen of high purity (99.999%) as carrier gas at a flow rate of 1 mL/min, injection port at 250 8C and FID at 300 8C. Temperature programs for the separations of different samples are individually provided in their figure captions.
http://dx.doi.org/10.1016/j.cclet.2014.10.001 1001-8417/ß 2014 Mei-Ling Qi. Published by Elsevier B.V. on behalf of Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. All rights reserved.
Y. Feng et al. / Chinese Chemical Letters 26 (2015) 47–49
48
comparable Y0 value (H-bond donor and acceptor) to that of the conventional Wax phase and lower S0 (H-bond acceptor) and Z0 (dipole–dipole interaction) values than the latter, suggesting that H-bonding and dipole–dipole interactions may play a major role in the retention of the GO stationary phase for analytes of different types.
Table 1 McReynolds constants of GO and HP-INNOWAX capillary columns. Column
X0
Y0
Z0
U0
S0
Sum
Average
GO HP-INNOWAX
127 322
517 536
230 368
374 572
293 510
1541 2308
308 462
X0 : benzene; Y0 : 1-butanol; Z0 : 2-pentanone; U0 : 1-nitropropane; S0 : pyridine.
3.2. Separation performance 2.2. Capillary column fabrication Separation performance of the GO capillary column was evaluated by GC separations of analytes of different functionalities, including n-alkanes, aromatic hydrocarbons, alcohols, amines and a mixture of 11 analytes. The corresponding GC separation chromatograms are shown in Figs. 1–3, respectively. Fig. 1 describes the GC separations of n-alkanes (a), aromatic hydrocarbons (b) and alcohols (c) on the GO column, respectively, showing the good separation performance of GO stationary phase for analytes from non-polar to polar. Especially, the GO stationary phase exhibited good peak shapes for alcohols that are known to be prone to peak tailing in GC analysis due to their strong H-bonding tendencies with a polar stationary phase. This suggests moderate interactions with alcohols as well as good column inertness. Based on this finding, we proceeded to further investigate the separation performance of GO capillary column for other H-bonding analytes, such as amines. Fig. 2 shows the GC separations of amines on GO (a) and conventional Wax (b) capillary columns, respectively. Amines are proton-acceptor and liable to peak tailing in GC analysis. As can be observed, the GO column exhibited good peak shapes, especially for di-n-hexylamine (peak 2) and dodecylamine (peak 3). Dodecylamine had a shortened peak height on the commercial column, suggesting the possible existence of active sites on the indicated column. The above results demonstrated the good separation performance of the GO stationary phase for H-bonding analytes, such as alcohols and amines. Fig. 3 presents the GC separations of a mixture of 11 analytes on GO (a) and conventional Wax (b) capillary columns. As shown, the GO stationary phase achieved baseline resolution for all the analytes and exhibited different retention behaviors for some of the analytes from the conventional Wax phase. Specifically, the GO stationary phase completely resolved chlorobenzene (peak 2) and n-dodecane (peak 4), which were partially separated on the conventional phase (R = 0.66). Of particular note, the nonpolar analytes, such as n-dodecane (peak 4) and methyl nonanoate (peak 7) are retained longer on the GO column, which eluted earlier on the Wax column and resulted in the switched elution order of
The capillary column coated with GO was fabricated as follows. First, a bare capillary column (5 m 0.25 mm) was rinsed with dichloromethane for 10 min, heated at 100 8C for 10 min, washed with 1.0 mol/L sodium hydroxide for 1.5 h and then with water until the eluate was neutral. After this, the column was heated at 120 8C for 2.0 h. Then, a GO dispersion was prepared by dispersing 200 mL GO aqueous solution (1 mg/mL) in a mixture of 100 mL 3AMDS and 500 mL ethanol under ultrasonication for 10 min. Next, the capillary was filled with the GO dispersion and maintained at room temperature for 1.0 h with both ends sealed. Afterwards, it was conditioned from 40 8C to 170 8C at 1 8C/min and held at the high-end temperature for 5 h under nitrogen flow. Finally, the capillary column coated with GO nanosheets was obtained and used for the following GC separations.
3. Results and discussion 3.1. McReynolds constants and column efficiency Column efficiency of the GO column was determined with naphthalene at 120 8C. The determined height equivalent to a theoretical plate (HETP) was 0.74 mm, corresponding to the column efficiency of 1350 plates/m. McReynolds constants are an empirical measure of the polarity of a GC stationary phase for the characterization of the possible interactions of a stationary phase with analytes. They can be experimentally measured by determining the differences of five probes, namely benzene (X0 ), 1-butanol (Y0 ), 2-pentanone (Z0 ), 1-nitropropane (U0 ) and pyridine (S0 ), in the retention indices on the given stationary phase and squalane. The sum and average of the retention index differences (DI) for the five probes correspond to a measure of the overall polarity and average polarity of a GC stationary phase, respectively. Table 1 shows the resulting McReynolds constants (DI) and their sum and average values of the GO capillary column, suggesting its moderately polar nature. As shown, it exhibits 1
(a)
500
3
4
5
500
8 4
300 pA
pA
200
7
6
150
200
5
50 0
2
4
6
Time (min)
8
10
0
5 2
300
7 6
8 10
3 9
200
3
100
4
400
1
100
0
(c)
600
2
400
2
250
1
700
(b)
300
pA
350
100
0
5
10 Time (min)
15
20
0
0
2
4
6 8 Time (min)
10
12
14
Fig. 1. GC separations of n-alkanes (a) aromatic hydrocarbons (b) and alcohols (c) on GO capillary column. Peaks for (a): (1) n-nonane, (2) n-decane, (3) n-undecane, (4) ndodecane, (5) n-tridecane; (6) n-tetradecane, (7) n-pentadecane and (8) n-hexadecane; for (b): (1) naphthalene, (2) biphenyl, (3) fluorene, (4) phenanthrene and (5) fluoranthene; for (c): (1) 1-propanol, (2) 1-butanol, (3) 1-pentanol, (4) 1-hexanol, (5) 1-heptanol, (6) 1-octanol, (7) 1-nonanol, (8) 1-decanol, (9) 1-undecanol and (10) 1dodecanol. Temperature programs: (a) 40 8C (1 min) to 130 8C at 10 8C/min, (b) 40 8C (1 min) to 160 8C at 10 8C/min and (c) 40 8C (1 min) to 140 8C at 10 8C/min.
Y. Feng et al. / Chinese Chemical Letters 26 (2015) 47–49
49
Fig. 2. GC separations of amines on GO (a) and HP-INNOWAX (b) capillary columns. Peaks: (1) dimethylformamide, (2) di-n-hexylamine, (3) dodecylamine, (4) di-noctylamine. Temperature programs: (a) 40 8C (1 min) to 150 8C at 10 8C/min and (b) 40 8C (1 min) to 200 8C at 10 8C/min.
Fig. 3. GC separations of a mixture of 11 analytes on GO (a) and HP-INNOWAX (b) capillary columns. Peaks: (1) toluene, (2) chlorobenzene, (3) bromobenzene, (4) n-dodecane, (5) 1,2-dichlorobenzene, (6) benzonitrile, (7) methyl nonanoate, (8) naphthalene, (9) aniline, (10) 3-toluidine and (11) biphenyl. Temperature program: 30 8C (1 min) to 140 8C at 10 8C/min.
bromobenzene/n-dodecane (peaks 3/4) and 1,2-dichlorobenzene/ benzonitrile (peaks 5/6), demonstrating their different separation performance and retention behaviors. Additionally, separation reproducibility of GO column in retention times of analytes was examined by separation of the mixture of 11 analytes. The obtained relative standard deviations (RSD%) were in the range of 0.03%–0.24% (n = 5), indicating the good reproducibility of GO column for the GC separations. 4. Conclusion This work describes the separation performance of GO nanosheets as a capillary GC stationary phase. The GO column fabricated by a new single-step coating approach exhibited different resolving ability from the conventional Wax column and achieved good peak shapes for H-bonding analytes, such as alcohols and amines that are prone to peak-tailing in GC analysis. These differences may originate from their different molecular interactions. The GO stationary phase exhibits moderate H-bonding and dipole–dipole interactions with H-bonding analytes and offers stronger p–p interactions with aromatic analytes than the latter. The comprehensive result of these molecular interactions distinguishes the GO stationary phase from the conventional stationary phase in term of retention behaviors and resolving ability. Acknowledgments This work was supported by the National Natural Science Foundation of China (Nos. 21075010, 21174019) and the 111 Project B07012 in China.
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