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A highly selective fluorescent probe for the determination of Se(IV) in multivitamin tablets
Sensors and Actuators B 193 (2014) 592–598
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A highly selective fluorescent probe for the determination of Se(IV) in multivitamin tablets Guodong Feng a,b , Yanna Dai a , Haiyan Jin a , Pengchong Xue a , Yanfu Huan a , Hongyan Shan a , Qiang Fei a,∗ a b
College of Chemistry, Jilin University, Changchun 130021, PR China State key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e
i n f o
Article history: Received 8 August 2013 Received in revised form 2 November 2013 Accepted 28 November 2013 Available online 7 December 2013 Keywords: Rhodamine 6G Diethylenetriamine Fluorescent probe Enhancement Selenium Multivitamins
a b s t r a c t An inducible fluorescent ligand 2-(2-(2-aminoethylamino)ethyl)-3 ,6 -bis(ethylamino)-2 ,7 dimethylspiro[isoindoline-1,9 -xanthen]-3-one was synthesized and used as a fluorescent probe to detect Se(IV). Se(IV) induced the structural transformation of the fluorescent ligand, resulting in a sharp fluorescence emission in an ethanol system. The fluorescence intensity observed was directly proportional to the concentration of Se ions. The detection limit of Se(IV) was 2.8 × 10−9 mol L−1 under optimized conditions. The Se(IV) concentrations in four multivitamins were determined, and have obtained a tiny deviation of 2% compared with the result detected by ICP-AES. The recovery of Se(IV) in four samples ranged from 98% to 103%. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Selenium (Se) is an important metalloid with industrial, environmental, biological, and toxicological significance. It is recognized as a nutrient element essential to most mammalian species. Se participates actively in protein synthesis. About 50 proteins in bacteria, archaea, and mammals contain Se [1]. The metalloid fulfills important roles in anticarcinogenic activity and protection against the toxic effects of heavy metals [2,3]. However, only a narrow range of selenium concentrations (70 g to 100 g per day) is beneficial to human health. Beyond this range, Se deficiency or poisoning can cause diseases [4]. Hence, the accurate determination of micro or trace amounts of Se is of great importance in the medical, nutritional, and environmental sciences. Se exists in both inorganic and organic forms. Inorganic Se species are more toxic than organic ones. Toxicological experiments have confirmed that selenite (SeO2− 3 ) is more toxic than selenate [5,6]. Na2 SeO3 has also been found to induce substantial DNA damage in human fibroblasts [7] and is a potentially problematic ingredient found in many mass-market multivitamins. Thus, the detection of SeO2− 3 is much more important than that of total Se.
∗ Corresponing author. Tel.: +86 431 88499976; fax: +86 431 88499805. E-mail address: [email protected] (Q. Fei). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.11.115
Many techniques for the determination of selenium have been reported over the years. Various atomic detection techniques, including hydride generation (HG) or graphite furnace atomic absorption spectrometry [8–13], hydride generation atomic fluorescence spectrometry (HG-AFS) [4,14,15], and inductively coupled plasma atomic emission spectrometry (ICP-AES) [16–19], have been used to detect inorganic selenium species. In recent years, other approaches, including high-performance liquid chromatography [20], capillary electrophoresis [3,21,22], electrothermal vaporization [23] coupled to ICP-MS [24], X-ray fluorescence spectrometry [25], and neutron activation analysis [26], have also been used for the detection of Se. Among these methods, HGAFS, ICP-AES, and ICP-MS exhibit more advantages for trace Se determination in biological materials and environmental samples. Nevertheless, the drawbacks of HG are fairly obvious. For example, the interference of transition metals (such as Co2+ , Ni2+ , and Fe2+ ) and instability of tetrahydroborate (THB) affect determination results, and, more seriously, THB-HG efficiency is affected significantly by the chemical form or oxidation state of the targeted elements [27]. While ICP-AES shows great sensitivity, background radiation from other elements and the plasma gases negatively influence the results obtained from the method. Furthermore, ICPMS is not available in most laboratories because of the high price and maintenance costs of the analytical equipment. It also suffers from isobaric interference between the dominant isotope of selenium and the argon dimer, Ar2 (both with masses of 80) [25].
G. Feng et al. / Sensors and Actuators B 193 (2014) 592–598
In recent years, many efforts have been made to design various selective chemosensors for Se ion detection. Fluorescent Se ion sensors [28–35] are very attractive because they are highly efficient for discriminating target analytes over the inherent spectrally complex background in real-world samples. In previous reports, the fluorophore was always produced by association of Se with 2,3diaminanaphthalene (DAN). However, the Se-DAN complex formed in aqueous medium must be extracted with organic solvents, in order to eliminate interferences and improve the sensitivity for detection, which could lead to analyte loss and contamination. As well, the color development of Se-DAN requires long waiting times (110 min) [27]. In the current work, the organic ligand 2-(2-(2-aminoethylamino) ethyl)-3 ,6 -bis(ethylamino)-2 ,7 -dimethylspiro[isoindoline-1,9 -xanthen]-3-one (ABDO), was used as novel fluorescent probe for Se(IV) detection. This fluorescent probe showed excellent selectivity and sensitivity toward Se(IV). The detection limit of Se(IV) was 2.8 × 10−9 mol L−1 (0.22 g L−1 ). The detection limit using ABDO was lower than the previously reported data by fluorescence method directly in the literatures [28,32,33,35].The ABDO fluorescent ligand was applied in the determination of Se(IV) from four mass-market multivitamin tablets, and have obtained a tiny deviation of 2% compared with the result detected by ICP-AES. The recovery of Se(IV) in four samples ranged from 98% to 103%. 2. Materials and methods 2.1. Materials All reagents were of analytical grade and used without further purification. Rhodamine 6G was purchased from acros organics (Fair Lawn, NJ, USA). Diethylenetriamine was purchased from J&K technology Co., Ltd. (Beijing, China). Ethanol, acetonitrile, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ethyl acetate, chloroforms and methylene chloride were purchased from Beijing Chemical Reagent Corporation (Beijing, China). HEPES was purchased from Beijing Dingguo Changsheng Biotechnology Co. Ltd. (Beijing, China). The solutions of metal ions were prepared from their salts which were purchased from Beijing Chemical Reagent Corporation (Beijing, China). Double-distilled water was used throughout all experiments. 2.2. The synthesis of ABDO Compound (ABDO) was synthesized according to the literature with small modification (Scheme 1) [36,37]. Rhodamine 6G (1.916 g, 4.0 mmol) was dissolved in 20 mL of hot ethanol, followed by the addition of diethylenetriamine (3 mL, 28 mmol). The reaction mixture was refluxed for 24 h till the green fluorescence of the solution was disappeared. After cooled to the room temperature, the mixture was evaporated in vacuum in order to remove some ethanol. Then double-distilled water was added in the mixture, and the pink solid formed was filtered and washed 2–3 times with double-distilled water. This solid was then recrystallized in hot ethanol aqueous solution to give 1.62 g of ABDO (yield 75%). 1 H NMR (300 MHz, CDCl3): ı(ppm):7.90 (m,1H), 7.45 (t, J = 3.75 Hz, 2H), 7.02 (m, 1H), 6.34 (s, 2H), 6.23 (s, 2H), 3.50 (d, J = 4.2 Hz, 2H),
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3.21 (m, 6H), 2.58 (t, J = 6 Hz, 2H), 2.41 (t, J = 6.6 Hz, 4H), 1.90 (s, 6H), 1.43 (s, 3H), 1.32 (t, J = 7.05 Hz, 6H); MS (ESI) m/z obsd 500.5 ([M + H+ ] calcd 500.5 for C30 H37 N5 O2 ). 2.3. Digestion procedure of sample HCl (6 mL) and HNO3 (2 mL) were added to the sample (2.0 g) in a round-bottom flask. The mixture was heated gradually until heavy evolution of fume ceased. When carbonization appeared, the vessel was removed from heating, after the vessel was cooled down to the room temperature, HNO3 (1 mL) was added. The mixture was then heated again. The residue was dissolved with 2 mL of 6 mol L−1 HCl and the resulting mixture was heated to 100 ◦ C for 5 min in order to reduce Se(VI) to Se(IV) [38]. The final residue was dissolved in 10 mL HEPES buffer (0.1 mol L−1 , pH = 7.0) and the resulting solution was referred to as the sample solution. 2.4. Determination of Se(IV) The compound (ABDO) was characterized with a Varian Mercury YH-300 nuclear magnetic resonance instrument (Varian, USA) and a Q-Trap2000 LC–MS (Applied Biosystems Company, USA). The absorption spectra were obtained using a UV-2550 spectrophotometer (Shimadzu Corporation, Japan). Inductively coupled plasma (ICP) analysis was performed on the optima 3300 DV ICP spectrometer (Perkin Elmer, USA). An RF-5301PC spectrophotofluorometer (Shimadzu Corporation, Japan) was used throughout the whole experiment. The ABDO was dissolved in ethanol to get a 1 mmol L−1 standard solution. 30 L of ABDO ethanol solution was added into 3 mL water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) containing Se(IV), and then the solution was allowed to stand for 20 min at 25 ◦ C before fluorescence measurement. The fluorescence intensity was measured at wavelength of 550 nm when the excitation wavelength was 510 nm. A quartz cell of 1 cm path length was used. Both the excitation and emission slits were set at 5.0 nm. 3. Results and discussion 3.1. Absorption and fluorescence properties of ABDO The absorption spectra of ABDO in the presence of Se(IV) in a water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) were recorded, and the results are shown in Fig. 1A. ABDO did not show typical rhodamine-framework absorption in the wavelength range from 400 to 600 nm because of its stable “spirolactam form.” However, typical rhodamine absorption at 527 nm appeared in the presence of Se(IV), and the absorbance of ABDO increased with increasing Se(IV) concentration. Job’s plot analysis was applied to the ABDO-Se(IV) complex. The observed binding curve could be fitted to a 1:1 binding model and gave an apparent association constant (Ka) of 9.0 × 105 M−1 (see Fig. S3 in Supplementary material). The fluorescence excitation and emission spectra of ABDO in a water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) are shown in Fig. 1B (lines a and b). ABDO exhibited almost no fluorescence signal at an excitation wavelength of 530 nm.
Scheme 1. Synthesis pathway of ABDO.
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Fig. 1. Absorption spectra of ABDO-Se(IV) complex (Se, 1–10 M) (A) and fluorescence spectra of ABDO-Se(IV) complex (Se, 10 M) (B). (a) Excitation spectrum of ABDO (10 M), (b) Emission spectrum of ABDO (10 M), (c) excitation spectrum of ABDO-Se(IV), (d) emission spectrum of ABDO-Se(IV).
Fig. 2. Proposed mechanism for the fluorescence enhancement of ABDO in the presence of Se(IV).
This observation coincides with the non-fluorescent spirocyclic structure of ABDO. Interestingly, Se(IV) affected the fluorescence emission of ABDO. As seen in Fig. 1B (lines c and d), the fluorescence emission intensity of ABDO significantly increased in the presence of Se(IV). At an excitation wavelength of 530 nm, however, the emission spectrum obtained was not complete. Therefore, 510 nm was chosen as the excitation wavelength for subsequent experiments. At an excitation wavelength of 510 nm, the fluorescence emission intensity of Rhodamine 6G with Se(IV) was explored (see Fig. S4 in Supplementary Material). The fluorescence intensity of Rhodamine 6G did not change in the presence of Se(IV). The high fluorescence intensity of ABDO is due to its structural transformation from a spirocyclic form into its open-ring form by Se(IV) induction. The 1 H NMR spectra of ABDO before and after addition of Na2 SeO3 (see Fig. S5 in Supplementary Material) show that the proton of the phenyl ring adjacent to the carbonyl group shifted to a higher field, which suggests that the spirocyclic form of ABDO had opened and transformed into an open-ring form. This result is in agreement with data based on absorption and fluorescence spectra. In addition, the NMR peaks of all four CH2 -linked aliphatic amino moieties showed significant shifts after the addition of Na2 SeO3 , which indicates that the aliphatic amino units are the most likely to chelate with Na2 SeO3 [39]. We speculated that the spirolactam form of ABDO is opened in the presence of Se(IV) to form a highly delocalized -conjugated structure (Fig. 2). The ESI mass spectrum of the ABDO-Se(IV) complex was recorded at room temperature. ABDO shows a molecular ion peak at m/z 500.3, which corresponds to [ABDO + H] peak as the calculated m/z being 499. The ion peaks at m/z 413.3, 440.3, and 457.3 represent the fragments of ABDO. When the Se(IV) standard solution was added to the ABDO ethanol solution, the protonated molecular ion peak of Se-ABDO complex was observed in the 625.2–630.2 Da mass range. These peaks were separated by 1 Da mass difference because of the isotopic distributions of carbon and Se [40]. The isotopic peak distributions overlapped exactly with the theoretical mass
of the Se-ABDO complex calculated from the elemental composition of the complex (see Figs. S6–S8 in Supplementary material). The molecular ion peaks support the structure of the complex and confirm the stoichiometry of the metal chelate as the ML type. 3.2. Effect of different solvents on the fluorescence response Common organic solvents, including ethanol, acetonitrile, DMSO, DMF, ethyl acetate, chloroform, and methylene chloride, were tested. The effects of the solvents on the fluorescence response of the ABDO-Se(IV) complex are shown in Fig. 3. The fluorescence emission intensity of ABDO-Se(IV) was remarkably enhanced in the ethanol and ethyl acetate systems, and no obvious fluorescence
Fig. 3. Fluorescence intensity (550 nm) of ABDO (1 M) with and without Se(IV) (1 M) in different solvents. (The slit: 5, 5).
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Fig. 4. Effect of different pH on fluorescence intensity of ABDO-Se(IV) (1 M). [ABDO: 1 M; Se: 1 M; the slit: (5, 5)].
intensity enhancement was observed in other solvents. We chose ethanol as the system solvent in subsequent experiments. 3.3. Effect of different pH on the fluorescence response The effects of different pH on fluorescence intensity of ABDO-Se have been explored. As shown in Fig. 4, the fluorescence emission intensity (excitation at 510 nm) of ABDO started to increase quickly with pH from 6 to 2. This phenomena implied that the spirolactam form of ABDO could be opened with pH lower than 6. ABDO did not display any obvious and characteristic fluorescence at a pH range from 6 to 10, suggesting that it was stable over the pH range of 6 to 10 and could work in real sample with very low background fluorescence. In the presence of selenium, there was an obvious fluorescence off-on change of ABDO. The fluorescence intensity remained nearly constant between pH 6 and 10 (Fig. 4). Therefore, pH 7.0 was chosen for the fluorescence intensity determination as we mentioned in the article. 3.4. Effect of water content on the fluorescence response The effects of water content on the fluorescence intensity of Se(IV) in an ABDO ethanol solution were investigated. Experimental results show that the fluorescence characteristics of ABDO do not obviously change in solutions with water contents ranging from 1% to 20% (Fig. 5). However, in the presence of Se(IV), the fluorescence intensity change of ABDO became inconspicuous under water contents ranging from 1% to 5%. At water contents ranging from 5% to 20%, remarkable fluorescence intensity changes in ABDO with different fluorescence quenching efficiencies were observed. The fluorescence quenching mechanism is due to the water-induced nonradiative processes that relevant to the formation of hydrogen bonds between the entire excited ABDO-Se(IV) complex molecules and water clusters, which results in fluorescence quenching [41,42]. Therefore, the water content of the ABDO detection system not exceeds 5%. 3.5. Effect of reaction parameters on the fluorescence response The effect of reaction time on fluorescence intensity of the ABDO-Se(IV) complex was studied at room temperature. Fig. 6A shows that the fluorescence intensity of free ABDO was very low and the fluorescence signal of ABDO in the presence of Se(IV) increased sharply in the water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0). The fluorescence intensity reached the maximum value within 20 min and remained nearly constant thereafter,
Fig. 5. Effect of water content on fluorescence intensity of ABDO-Se(IV) [ABDO: 1 M; Se: 1 M; the slit: (5, 5)].
which demonstrates that the ABDO-Se(IV) complex can be formed. Therefore, a reaction time of 20 min was selected in subsequent experiments. The effect of reaction temperature was also studied. Fig. 6B shows that the fluorescence response of ABDO initially increased with temperature, reached a maximum at 20 ◦ C, and then remained nearly constant from 20 to 25 ◦ C, which means that elevated temperatures may be helpful in accelerating the complexation reaction. However, with further increases in temperature, the fluorescence response decreased. We speculate that the stability of such a complex begins to decrease at temperatures over 25 ◦ C. Therefore, 25 ◦ C was selected as the optimal reaction temperature for subsequent experiments. 3.6. Interference of common ions in Se(IV) detection The effect of common metal ions was investigated. Fig. 7A shows that the color of Se4+ solution changes from colorless to pink in the water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0); by contrast, the colors of other metal ion solutions did not change. Among the metal ions tested (Ca2+ , Hg2+ , Zn2+ , Cr6+ , Li+ , Sr2+ , Na+ , Ni2+ , Al3+ , K+ , Co2+ , Mo6+ , Rb+ , Mn2+ , Cs+ , Cd2+ , Ba2+ , Fe3+ , Cu2+ , Ag+ , 2− Be2+ , and SeO2− 3 ), only SeO3 can induce the yellow fluorescence of ABDO (Fig. 7B). The interference of common metal ions during Se(IV) detection was also investigated. Fig. 7C illustrates the fluorescence response of ABDO in the presence of different metal ions. No obvious fluorescence signal was observed in the presence of metal ions, which indicates that other metal ions cannot induce the structural transformation of ABDO. Furthermore, the fluorescence 4+ and intensity of ABDO had no obvious increment after SeO2− 4 , Se Se2− were added, then emitted strong florescence in the presence of SeO2− 3 (see Fig. S10 in Supplementary material). Thus, the probe exhibits high selectivity toward Se(IV). To test the practical applicability of our fluorescence chemosensor for detecting Se(IV), competition experiments were carried out. A sample solution containing the aforementioned metal ions (100 mol L−1 ) and 10 mol L−1 of Se(IV) and a sample solution containing only 10 mol L−1 of Se(IV) were analyzed. Results are also shown in Fig. 7C. The fluorescence intensity remained almost unchanged before and after addition of other interfering metal ions. These experimental results show that the response of the sensor to Se(IV) is unaffected by other potentially contaminating metal ions, which indicates that the coordinate moiety of ABDO perfectly matches Se(IV) and not other metal ions.
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Fig. 6. Effect of time ((A) slit: 2.5, 2.5) and temperature ((B) slit: 5, 5) on the fluorescence intensity of ABDO (1 M) with and without Se(IV) (1 M).
Fig. 7. Color change (A) and fluorescence change (B) of the system and Column diagram of Metal ion selectivity of probe (C). [ABDO, 10 mol L−1 ; Se, 10 mol L−1 and 100 mol L−1 for all remaining ions in HEPES buffer (0.1 mol L−1 , pH = 7.0); Black bars: different metal ions were added. Red bars: different metal ions in the presence of Se(IV) were added, measured at the slit (2.5, 2.5)]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
A test to determine interferences from a number of common anions in the detection of Se(IV) was also carried out at an excitation wavelength of 510 nm and an emission wavelength of 550 nm (see Fig. S11 in Supplementary material). No obvious fluorescence signals were observed with common interference anions, 2− − − 2− − − such as CO2− 3 , HCO3 , H2 PO4 , HPO4 , CH3 COO , Cl , Br , S ,
2− 2− SeO2− 3 , S2 O8 , and SeO4 . In the competition experiments, a sample solution containing the aforementioned anions (10 mol L−1 ) was added to 1 mol L−1 of Se(IV), and a sample solution containing only 1 mol L−1 of Se(IV) were analyzed. The response of the proposed sensor to Se(IV) was unaffected by the presence of other potentially contaminating anions.
3.7. Analytical characteristics Under optimized conditions, the fluorescence response of ABDO increased with increasing Se(IV) concentration in the range of 10 nmol L−1 to 3 mol L−1 (Fig. 8A). As shown in Fig. 8B, the fluorescence emission intensity of ABDO increased with increasing concentration of Se(IV) at 550 nm. ABDO showed a good linear relationship with Se(IV) concentrations ranging from 10 nmol L−1 to 100 nmol L−1 . The limit of detection of Se(IV) was 2.8 × 10−9 mol L−1 (based on S/N = 3). Therefore, the presented method provides a high-sensitivity fluorescence probe that may be used for the detection of Se(IV) in actual samples.
Fig. 8. (A) Fluorescence spectra of ABDO (1 mol L−1 ) with the addition of increasing concentrations of Se(IV) (10 nmol L−1 –3 mol L−1 ) in ethanol solution with a Measure slit at (5, 2.5); (B) Fluorescent intensity (550 nm) of ABDO after the addition of Se(IV) (10 nmol L−1 –3 mol L−1 ). Inset: linearity of the fluorescence at 550 nm with respect to the Se(IV) concentration over the range of 10–100 nmol L−1 .
G. Feng et al. / Sensors and Actuators B 193 (2014) 592–598 Table 1 Results of the sample analysis and recovery of spiked Se(IV) in multivitamin tablets. Sample
Founda (nM)
Foundb (nM)
Se spikedb (nM)
Se foundb (nM)
Recoveryb (%)
1 2
180 0
185 0
3
0
0
4
0
0
– 200 600 200 600 200 600
– 198 612 199 616 202 615
– 98.8 102.0 99.5 102.7 100.8 102.5
a b
Detected by ICP-AES method. Detected by the method of this paper.
3.8. Analysis of the target element in health care products To test the reliability of the present method, Se(IV) concentrations in four mass-market multivitamins were determined. Actual samples were collected from multivitamin tablets and pretreated by the wet digestion method. The Se(IV) concentrations of the samples were determined using an optimized fluorimetric procedure, and the results obtained are summarized in Table 1. The concentrations of Se(IV) in sample 1 determined by the present method are consistent with values obtained by ICP-AES. The Se(IV) concentration using ABDO has been carried out and obtained a tiny deviation of 2% compared with the result detected by ICP-AES. Se(IV) was not detected in the three other samples. Recovery experiments for various amounts of Se(IV) were carried out, and experimental results are also shown in Table 1. The results obtained confirm the validity of the present method. 4. Conclusions In summary, a highly selective and sensitive fluorescent probe for Se(IV) in 5% aqueous ethanol solution was developed. The system is monitored by colorimetric and fluorescence intensity changes. The selectivity of the proposed method for determining Se(IV) was remarkably high, and its detection limit was 2.8 × 10−9 mol L−1 (0.22 g L−1 ). The experimental results suggest that the proposed probe may serve as a foundation of practical fluorescent methods for rapidly determining Se(IV) in actual samples. Acknowledgments We are grateful for financial support from the National Major Scientific Instruments Development Project of china (2011YQ14015001), the Major project of Jilin Province Science and Technology Development plan (20126018, 20130206014GX), the Science and Technology Development Project of Jilin Province of China (No. 201105008), Program for the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry open project (No. 2014-07). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2013.11.115. References [1] A. Kyriakopolos, D. Behne, R. Physiol, Selenium-containing proteins in mammals and other forms of life, Rev. Physiol. Biochem. Pharmacol. 145 (2002) 1–46. [2] K. Li, S.F.Y. Li, Speciation of selenium and Arsenic compounds in natural waters by capillary zone electrophoresis after on-column preconcentration with fieldamplified injection, Analyst 120 (1995) 361–366. [3] K. Pyrzynska, Analysis of selenium species by capillary electrophoresis, Talanta 55 (2001) 657–667.
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G. Feng et al. / Sensors and Actuators B 193 (2014) 592–598 and speciation with atomic fluorescence spectrometry and inductively coupled plasma mass spectrometry, Anal. Chem. 84 (2012) 2974–2981. K.N. Ramachandran, G.S. Kumar, Modified spectrophotometric method for the determination of selenium in environmental and mineral mixtures using 2,3diaminonaphthalene, Talanta 43 (1996) 1711–1714. E.M. Rodriguez Rodriguez, M. Sanz Alaejos, C. Diaz Romero, Enhancement of the fluorescence intensity of Se-2,3-diaminonaphthalene complex in aqueous solution by adding organic solvents, Anal. Chim. Acta 334 (1996) 161–166. J.H. Watkinson, Fluorometric determination of selenium in biological material with 2,3-diaminonaphthalene, Anal. Chem. 38 (1966) 92–97. X.R. Huang, N.Q. Jie, W.J. Zhang, Y.Q. Yin, H. Shao, Study on the spectrophotometric determination of micro amounts of selenium(IV) with 2,3-diaminonaphthalene in the presence of sodium dodecylsulphate, Fresenius J. Anal. Chem. 354 (1996) 195–199. I. Harrison, D. Littlejohn, G.S. Fell, Improved molecular fluorescence method for the determination of selenium in biological samples, Analyst 121 (1996) 1641–1646. M.C. Sheffield, T.M. Nahir, Analysis of selenium in Brazil nuts by microwave digestion and fluorescence detection, J. Chem. Educ. 79 (2002) 1345–1347. T. Warashina, H. Hoshino, T. Yotsuyanagi, Successive determinations of platinum(II) and selenium(IV) with 1,4-dibromo-2,3-diaminonaphthalene in aqueous micellar solutions, Anal. Sci. 17 (2001) 859–863. J.G. Li, Y.R. Wang, Y.Q. Wei, Y.L. Tang, Determination of trace Selenium in tea leaves based on fluorescence quenching with Se(IV) in Rhodamine 6G System, Chin. J. Anal. Lab. 5 (1997) 52–54. J. Mao, Q. He, W.S. Liu, An rodamine-based fluorescence probe for iron(ш) ion determination in aqueous solution, Talanta 80 (2010) 2093–2098. D.T. Quang, J.S. Wu, N.D. Luyen, T. Duong, N.D. Dan, N.C. Bao, P.T. Quy, Rhodamine-derived Schiff base for the selective determination of mercuric ions in water media, Spectrochim. Acta, Part A 78 (2011) 753–756. G. Somer, A. Nakisci Unlu, The effect of acid digestion on the recoveries of trace elements: recommended policies for the elimination of losses, Turk. J. Chem. 30 (2006) 745–753. S. Shim, J. Tae, Rhodamine cyclen-based fluourescent chemosensor for the detection of Cd2+ , Bull. Korean Chem. Soc. 32 (2011) 2928–2932.
[40] A. Yazici, N. Unüs¸, A. Altindal, B. Salih, O. Bekaro˘glu, Phthalocyanine with a giant dielectric constant, Dalton Trans. 41 (2012) 3773–3779. [41] S. Tobita, K. Ida, S. Shiobara, Water-induced fluorescence quenching of aniline and its derivatives in aqueous solution, Res. Chem. Intermed. 27 (2001) 205–218. [42] K. Alexander, S. Igor Yu, S. Zoya, A.L. Alexey, S.D. Andrey, Partitioning of 2,6bis(1H-benzimidazol-2-yl) pyridine fluorophore into a phospholipid bilayer: complementary use of fluorescence quenching studies and molecular dynamics simulations, Biol. Chem. 154 (2011) 8–17, O.
Biographies Guodong Feng is an associate professor in the College of Chemistry at Jilin University major in analytical chemistry. His current research interests are applications of optical sensor. Yanna Dai is studying her masters in the College of Chemistry at Jilin University. She received her B.Sc. in chemistry at Henan University in 2011. Haiyan Jin is a researcher in the College of Chemistry at Jilin University major in analytical chemistry. His current research interests are mass spectrometry. Pengchong Xue is an associate professor in the Department of Organic Chemistry, College of Chemistry at Jilin University. His current research interests are synthesis chemistry. Yanfu Huan is an associate professor in in the College of Chemistry at Jilin University major in analytical chemistry. Her current research interests are molecular recognition, sensors chemistry. Hongyan Shan is a researcher in the college of chemistry at Jilin University major in analytical chemistry. His current research interests are mass spectrometry. Qiang Fei is a lecturer in the College of Chemistry at Jilin University major in analytical chemistry.
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Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb
A highly selective fluorescent probe for the determination of Se(IV) in multivitamin tablets Guodong Feng a,b , Yanna Dai a , Haiyan Jin a , Pengchong Xue a , Yanfu Huan a , Hongyan Shan a , Qiang Fei a,∗ a b
College of Chemistry, Jilin University, Changchun 130021, PR China State key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, PR China
a r t i c l e
i n f o
Article history: Received 8 August 2013 Received in revised form 2 November 2013 Accepted 28 November 2013 Available online 7 December 2013 Keywords: Rhodamine 6G Diethylenetriamine Fluorescent probe Enhancement Selenium Multivitamins
a b s t r a c t An inducible fluorescent ligand 2-(2-(2-aminoethylamino)ethyl)-3 ,6 -bis(ethylamino)-2 ,7 dimethylspiro[isoindoline-1,9 -xanthen]-3-one was synthesized and used as a fluorescent probe to detect Se(IV). Se(IV) induced the structural transformation of the fluorescent ligand, resulting in a sharp fluorescence emission in an ethanol system. The fluorescence intensity observed was directly proportional to the concentration of Se ions. The detection limit of Se(IV) was 2.8 × 10−9 mol L−1 under optimized conditions. The Se(IV) concentrations in four multivitamins were determined, and have obtained a tiny deviation of 2% compared with the result detected by ICP-AES. The recovery of Se(IV) in four samples ranged from 98% to 103%. © 2013 Elsevier B.V. All rights reserved.
1. Introduction Selenium (Se) is an important metalloid with industrial, environmental, biological, and toxicological significance. It is recognized as a nutrient element essential to most mammalian species. Se participates actively in protein synthesis. About 50 proteins in bacteria, archaea, and mammals contain Se [1]. The metalloid fulfills important roles in anticarcinogenic activity and protection against the toxic effects of heavy metals [2,3]. However, only a narrow range of selenium concentrations (70 g to 100 g per day) is beneficial to human health. Beyond this range, Se deficiency or poisoning can cause diseases [4]. Hence, the accurate determination of micro or trace amounts of Se is of great importance in the medical, nutritional, and environmental sciences. Se exists in both inorganic and organic forms. Inorganic Se species are more toxic than organic ones. Toxicological experiments have confirmed that selenite (SeO2− 3 ) is more toxic than selenate [5,6]. Na2 SeO3 has also been found to induce substantial DNA damage in human fibroblasts [7] and is a potentially problematic ingredient found in many mass-market multivitamins. Thus, the detection of SeO2− 3 is much more important than that of total Se.
∗ Corresponing author. Tel.: +86 431 88499976; fax: +86 431 88499805. E-mail address: [email protected] (Q. Fei). 0925-4005/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.snb.2013.11.115
Many techniques for the determination of selenium have been reported over the years. Various atomic detection techniques, including hydride generation (HG) or graphite furnace atomic absorption spectrometry [8–13], hydride generation atomic fluorescence spectrometry (HG-AFS) [4,14,15], and inductively coupled plasma atomic emission spectrometry (ICP-AES) [16–19], have been used to detect inorganic selenium species. In recent years, other approaches, including high-performance liquid chromatography [20], capillary electrophoresis [3,21,22], electrothermal vaporization [23] coupled to ICP-MS [24], X-ray fluorescence spectrometry [25], and neutron activation analysis [26], have also been used for the detection of Se. Among these methods, HGAFS, ICP-AES, and ICP-MS exhibit more advantages for trace Se determination in biological materials and environmental samples. Nevertheless, the drawbacks of HG are fairly obvious. For example, the interference of transition metals (such as Co2+ , Ni2+ , and Fe2+ ) and instability of tetrahydroborate (THB) affect determination results, and, more seriously, THB-HG efficiency is affected significantly by the chemical form or oxidation state of the targeted elements [27]. While ICP-AES shows great sensitivity, background radiation from other elements and the plasma gases negatively influence the results obtained from the method. Furthermore, ICPMS is not available in most laboratories because of the high price and maintenance costs of the analytical equipment. It also suffers from isobaric interference between the dominant isotope of selenium and the argon dimer, Ar2 (both with masses of 80) [25].
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In recent years, many efforts have been made to design various selective chemosensors for Se ion detection. Fluorescent Se ion sensors [28–35] are very attractive because they are highly efficient for discriminating target analytes over the inherent spectrally complex background in real-world samples. In previous reports, the fluorophore was always produced by association of Se with 2,3diaminanaphthalene (DAN). However, the Se-DAN complex formed in aqueous medium must be extracted with organic solvents, in order to eliminate interferences and improve the sensitivity for detection, which could lead to analyte loss and contamination. As well, the color development of Se-DAN requires long waiting times (110 min) [27]. In the current work, the organic ligand 2-(2-(2-aminoethylamino) ethyl)-3 ,6 -bis(ethylamino)-2 ,7 -dimethylspiro[isoindoline-1,9 -xanthen]-3-one (ABDO), was used as novel fluorescent probe for Se(IV) detection. This fluorescent probe showed excellent selectivity and sensitivity toward Se(IV). The detection limit of Se(IV) was 2.8 × 10−9 mol L−1 (0.22 g L−1 ). The detection limit using ABDO was lower than the previously reported data by fluorescence method directly in the literatures [28,32,33,35].The ABDO fluorescent ligand was applied in the determination of Se(IV) from four mass-market multivitamin tablets, and have obtained a tiny deviation of 2% compared with the result detected by ICP-AES. The recovery of Se(IV) in four samples ranged from 98% to 103%. 2. Materials and methods 2.1. Materials All reagents were of analytical grade and used without further purification. Rhodamine 6G was purchased from acros organics (Fair Lawn, NJ, USA). Diethylenetriamine was purchased from J&K technology Co., Ltd. (Beijing, China). Ethanol, acetonitrile, dimethyl sulfoxide (DMSO), dimethylformamide (DMF), ethyl acetate, chloroforms and methylene chloride were purchased from Beijing Chemical Reagent Corporation (Beijing, China). HEPES was purchased from Beijing Dingguo Changsheng Biotechnology Co. Ltd. (Beijing, China). The solutions of metal ions were prepared from their salts which were purchased from Beijing Chemical Reagent Corporation (Beijing, China). Double-distilled water was used throughout all experiments. 2.2. The synthesis of ABDO Compound (ABDO) was synthesized according to the literature with small modification (Scheme 1) [36,37]. Rhodamine 6G (1.916 g, 4.0 mmol) was dissolved in 20 mL of hot ethanol, followed by the addition of diethylenetriamine (3 mL, 28 mmol). The reaction mixture was refluxed for 24 h till the green fluorescence of the solution was disappeared. After cooled to the room temperature, the mixture was evaporated in vacuum in order to remove some ethanol. Then double-distilled water was added in the mixture, and the pink solid formed was filtered and washed 2–3 times with double-distilled water. This solid was then recrystallized in hot ethanol aqueous solution to give 1.62 g of ABDO (yield 75%). 1 H NMR (300 MHz, CDCl3): ı(ppm):7.90 (m,1H), 7.45 (t, J = 3.75 Hz, 2H), 7.02 (m, 1H), 6.34 (s, 2H), 6.23 (s, 2H), 3.50 (d, J = 4.2 Hz, 2H),
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3.21 (m, 6H), 2.58 (t, J = 6 Hz, 2H), 2.41 (t, J = 6.6 Hz, 4H), 1.90 (s, 6H), 1.43 (s, 3H), 1.32 (t, J = 7.05 Hz, 6H); MS (ESI) m/z obsd 500.5 ([M + H+ ] calcd 500.5 for C30 H37 N5 O2 ). 2.3. Digestion procedure of sample HCl (6 mL) and HNO3 (2 mL) were added to the sample (2.0 g) in a round-bottom flask. The mixture was heated gradually until heavy evolution of fume ceased. When carbonization appeared, the vessel was removed from heating, after the vessel was cooled down to the room temperature, HNO3 (1 mL) was added. The mixture was then heated again. The residue was dissolved with 2 mL of 6 mol L−1 HCl and the resulting mixture was heated to 100 ◦ C for 5 min in order to reduce Se(VI) to Se(IV) [38]. The final residue was dissolved in 10 mL HEPES buffer (0.1 mol L−1 , pH = 7.0) and the resulting solution was referred to as the sample solution. 2.4. Determination of Se(IV) The compound (ABDO) was characterized with a Varian Mercury YH-300 nuclear magnetic resonance instrument (Varian, USA) and a Q-Trap2000 LC–MS (Applied Biosystems Company, USA). The absorption spectra were obtained using a UV-2550 spectrophotometer (Shimadzu Corporation, Japan). Inductively coupled plasma (ICP) analysis was performed on the optima 3300 DV ICP spectrometer (Perkin Elmer, USA). An RF-5301PC spectrophotofluorometer (Shimadzu Corporation, Japan) was used throughout the whole experiment. The ABDO was dissolved in ethanol to get a 1 mmol L−1 standard solution. 30 L of ABDO ethanol solution was added into 3 mL water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) containing Se(IV), and then the solution was allowed to stand for 20 min at 25 ◦ C before fluorescence measurement. The fluorescence intensity was measured at wavelength of 550 nm when the excitation wavelength was 510 nm. A quartz cell of 1 cm path length was used. Both the excitation and emission slits were set at 5.0 nm. 3. Results and discussion 3.1. Absorption and fluorescence properties of ABDO The absorption spectra of ABDO in the presence of Se(IV) in a water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) were recorded, and the results are shown in Fig. 1A. ABDO did not show typical rhodamine-framework absorption in the wavelength range from 400 to 600 nm because of its stable “spirolactam form.” However, typical rhodamine absorption at 527 nm appeared in the presence of Se(IV), and the absorbance of ABDO increased with increasing Se(IV) concentration. Job’s plot analysis was applied to the ABDO-Se(IV) complex. The observed binding curve could be fitted to a 1:1 binding model and gave an apparent association constant (Ka) of 9.0 × 105 M−1 (see Fig. S3 in Supplementary material). The fluorescence excitation and emission spectra of ABDO in a water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0) are shown in Fig. 1B (lines a and b). ABDO exhibited almost no fluorescence signal at an excitation wavelength of 530 nm.
Scheme 1. Synthesis pathway of ABDO.
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Fig. 1. Absorption spectra of ABDO-Se(IV) complex (Se, 1–10 M) (A) and fluorescence spectra of ABDO-Se(IV) complex (Se, 10 M) (B). (a) Excitation spectrum of ABDO (10 M), (b) Emission spectrum of ABDO (10 M), (c) excitation spectrum of ABDO-Se(IV), (d) emission spectrum of ABDO-Se(IV).
Fig. 2. Proposed mechanism for the fluorescence enhancement of ABDO in the presence of Se(IV).
This observation coincides with the non-fluorescent spirocyclic structure of ABDO. Interestingly, Se(IV) affected the fluorescence emission of ABDO. As seen in Fig. 1B (lines c and d), the fluorescence emission intensity of ABDO significantly increased in the presence of Se(IV). At an excitation wavelength of 530 nm, however, the emission spectrum obtained was not complete. Therefore, 510 nm was chosen as the excitation wavelength for subsequent experiments. At an excitation wavelength of 510 nm, the fluorescence emission intensity of Rhodamine 6G with Se(IV) was explored (see Fig. S4 in Supplementary Material). The fluorescence intensity of Rhodamine 6G did not change in the presence of Se(IV). The high fluorescence intensity of ABDO is due to its structural transformation from a spirocyclic form into its open-ring form by Se(IV) induction. The 1 H NMR spectra of ABDO before and after addition of Na2 SeO3 (see Fig. S5 in Supplementary Material) show that the proton of the phenyl ring adjacent to the carbonyl group shifted to a higher field, which suggests that the spirocyclic form of ABDO had opened and transformed into an open-ring form. This result is in agreement with data based on absorption and fluorescence spectra. In addition, the NMR peaks of all four CH2 -linked aliphatic amino moieties showed significant shifts after the addition of Na2 SeO3 , which indicates that the aliphatic amino units are the most likely to chelate with Na2 SeO3 [39]. We speculated that the spirolactam form of ABDO is opened in the presence of Se(IV) to form a highly delocalized -conjugated structure (Fig. 2). The ESI mass spectrum of the ABDO-Se(IV) complex was recorded at room temperature. ABDO shows a molecular ion peak at m/z 500.3, which corresponds to [ABDO + H] peak as the calculated m/z being 499. The ion peaks at m/z 413.3, 440.3, and 457.3 represent the fragments of ABDO. When the Se(IV) standard solution was added to the ABDO ethanol solution, the protonated molecular ion peak of Se-ABDO complex was observed in the 625.2–630.2 Da mass range. These peaks were separated by 1 Da mass difference because of the isotopic distributions of carbon and Se [40]. The isotopic peak distributions overlapped exactly with the theoretical mass
of the Se-ABDO complex calculated from the elemental composition of the complex (see Figs. S6–S8 in Supplementary material). The molecular ion peaks support the structure of the complex and confirm the stoichiometry of the metal chelate as the ML type. 3.2. Effect of different solvents on the fluorescence response Common organic solvents, including ethanol, acetonitrile, DMSO, DMF, ethyl acetate, chloroform, and methylene chloride, were tested. The effects of the solvents on the fluorescence response of the ABDO-Se(IV) complex are shown in Fig. 3. The fluorescence emission intensity of ABDO-Se(IV) was remarkably enhanced in the ethanol and ethyl acetate systems, and no obvious fluorescence
Fig. 3. Fluorescence intensity (550 nm) of ABDO (1 M) with and without Se(IV) (1 M) in different solvents. (The slit: 5, 5).
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Fig. 4. Effect of different pH on fluorescence intensity of ABDO-Se(IV) (1 M). [ABDO: 1 M; Se: 1 M; the slit: (5, 5)].
intensity enhancement was observed in other solvents. We chose ethanol as the system solvent in subsequent experiments. 3.3. Effect of different pH on the fluorescence response The effects of different pH on fluorescence intensity of ABDO-Se have been explored. As shown in Fig. 4, the fluorescence emission intensity (excitation at 510 nm) of ABDO started to increase quickly with pH from 6 to 2. This phenomena implied that the spirolactam form of ABDO could be opened with pH lower than 6. ABDO did not display any obvious and characteristic fluorescence at a pH range from 6 to 10, suggesting that it was stable over the pH range of 6 to 10 and could work in real sample with very low background fluorescence. In the presence of selenium, there was an obvious fluorescence off-on change of ABDO. The fluorescence intensity remained nearly constant between pH 6 and 10 (Fig. 4). Therefore, pH 7.0 was chosen for the fluorescence intensity determination as we mentioned in the article. 3.4. Effect of water content on the fluorescence response The effects of water content on the fluorescence intensity of Se(IV) in an ABDO ethanol solution were investigated. Experimental results show that the fluorescence characteristics of ABDO do not obviously change in solutions with water contents ranging from 1% to 20% (Fig. 5). However, in the presence of Se(IV), the fluorescence intensity change of ABDO became inconspicuous under water contents ranging from 1% to 5%. At water contents ranging from 5% to 20%, remarkable fluorescence intensity changes in ABDO with different fluorescence quenching efficiencies were observed. The fluorescence quenching mechanism is due to the water-induced nonradiative processes that relevant to the formation of hydrogen bonds between the entire excited ABDO-Se(IV) complex molecules and water clusters, which results in fluorescence quenching [41,42]. Therefore, the water content of the ABDO detection system not exceeds 5%. 3.5. Effect of reaction parameters on the fluorescence response The effect of reaction time on fluorescence intensity of the ABDO-Se(IV) complex was studied at room temperature. Fig. 6A shows that the fluorescence intensity of free ABDO was very low and the fluorescence signal of ABDO in the presence of Se(IV) increased sharply in the water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0). The fluorescence intensity reached the maximum value within 20 min and remained nearly constant thereafter,
Fig. 5. Effect of water content on fluorescence intensity of ABDO-Se(IV) [ABDO: 1 M; Se: 1 M; the slit: (5, 5)].
which demonstrates that the ABDO-Se(IV) complex can be formed. Therefore, a reaction time of 20 min was selected in subsequent experiments. The effect of reaction temperature was also studied. Fig. 6B shows that the fluorescence response of ABDO initially increased with temperature, reached a maximum at 20 ◦ C, and then remained nearly constant from 20 to 25 ◦ C, which means that elevated temperatures may be helpful in accelerating the complexation reaction. However, with further increases in temperature, the fluorescence response decreased. We speculate that the stability of such a complex begins to decrease at temperatures over 25 ◦ C. Therefore, 25 ◦ C was selected as the optimal reaction temperature for subsequent experiments. 3.6. Interference of common ions in Se(IV) detection The effect of common metal ions was investigated. Fig. 7A shows that the color of Se4+ solution changes from colorless to pink in the water/ethanol mixture (0.5:9.5 v/v; HEPES 0.1 mol L−1 ; pH = 7.0); by contrast, the colors of other metal ion solutions did not change. Among the metal ions tested (Ca2+ , Hg2+ , Zn2+ , Cr6+ , Li+ , Sr2+ , Na+ , Ni2+ , Al3+ , K+ , Co2+ , Mo6+ , Rb+ , Mn2+ , Cs+ , Cd2+ , Ba2+ , Fe3+ , Cu2+ , Ag+ , 2− Be2+ , and SeO2− 3 ), only SeO3 can induce the yellow fluorescence of ABDO (Fig. 7B). The interference of common metal ions during Se(IV) detection was also investigated. Fig. 7C illustrates the fluorescence response of ABDO in the presence of different metal ions. No obvious fluorescence signal was observed in the presence of metal ions, which indicates that other metal ions cannot induce the structural transformation of ABDO. Furthermore, the fluorescence 4+ and intensity of ABDO had no obvious increment after SeO2− 4 , Se Se2− were added, then emitted strong florescence in the presence of SeO2− 3 (see Fig. S10 in Supplementary material). Thus, the probe exhibits high selectivity toward Se(IV). To test the practical applicability of our fluorescence chemosensor for detecting Se(IV), competition experiments were carried out. A sample solution containing the aforementioned metal ions (100 mol L−1 ) and 10 mol L−1 of Se(IV) and a sample solution containing only 10 mol L−1 of Se(IV) were analyzed. Results are also shown in Fig. 7C. The fluorescence intensity remained almost unchanged before and after addition of other interfering metal ions. These experimental results show that the response of the sensor to Se(IV) is unaffected by other potentially contaminating metal ions, which indicates that the coordinate moiety of ABDO perfectly matches Se(IV) and not other metal ions.
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Fig. 6. Effect of time ((A) slit: 2.5, 2.5) and temperature ((B) slit: 5, 5) on the fluorescence intensity of ABDO (1 M) with and without Se(IV) (1 M).
Fig. 7. Color change (A) and fluorescence change (B) of the system and Column diagram of Metal ion selectivity of probe (C). [ABDO, 10 mol L−1 ; Se, 10 mol L−1 and 100 mol L−1 for all remaining ions in HEPES buffer (0.1 mol L−1 , pH = 7.0); Black bars: different metal ions were added. Red bars: different metal ions in the presence of Se(IV) were added, measured at the slit (2.5, 2.5)]. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
A test to determine interferences from a number of common anions in the detection of Se(IV) was also carried out at an excitation wavelength of 510 nm and an emission wavelength of 550 nm (see Fig. S11 in Supplementary material). No obvious fluorescence signals were observed with common interference anions, 2− − − 2− − − such as CO2− 3 , HCO3 , H2 PO4 , HPO4 , CH3 COO , Cl , Br , S ,
2− 2− SeO2− 3 , S2 O8 , and SeO4 . In the competition experiments, a sample solution containing the aforementioned anions (10 mol L−1 ) was added to 1 mol L−1 of Se(IV), and a sample solution containing only 1 mol L−1 of Se(IV) were analyzed. The response of the proposed sensor to Se(IV) was unaffected by the presence of other potentially contaminating anions.
3.7. Analytical characteristics Under optimized conditions, the fluorescence response of ABDO increased with increasing Se(IV) concentration in the range of 10 nmol L−1 to 3 mol L−1 (Fig. 8A). As shown in Fig. 8B, the fluorescence emission intensity of ABDO increased with increasing concentration of Se(IV) at 550 nm. ABDO showed a good linear relationship with Se(IV) concentrations ranging from 10 nmol L−1 to 100 nmol L−1 . The limit of detection of Se(IV) was 2.8 × 10−9 mol L−1 (based on S/N = 3). Therefore, the presented method provides a high-sensitivity fluorescence probe that may be used for the detection of Se(IV) in actual samples.
Fig. 8. (A) Fluorescence spectra of ABDO (1 mol L−1 ) with the addition of increasing concentrations of Se(IV) (10 nmol L−1 –3 mol L−1 ) in ethanol solution with a Measure slit at (5, 2.5); (B) Fluorescent intensity (550 nm) of ABDO after the addition of Se(IV) (10 nmol L−1 –3 mol L−1 ). Inset: linearity of the fluorescence at 550 nm with respect to the Se(IV) concentration over the range of 10–100 nmol L−1 .
G. Feng et al. / Sensors and Actuators B 193 (2014) 592–598 Table 1 Results of the sample analysis and recovery of spiked Se(IV) in multivitamin tablets. Sample
Founda (nM)
Foundb (nM)
Se spikedb (nM)
Se foundb (nM)
Recoveryb (%)
1 2
180 0
185 0
3
0
0
4
0
0
– 200 600 200 600 200 600
– 198 612 199 616 202 615
– 98.8 102.0 99.5 102.7 100.8 102.5
a b
Detected by ICP-AES method. Detected by the method of this paper.
3.8. Analysis of the target element in health care products To test the reliability of the present method, Se(IV) concentrations in four mass-market multivitamins were determined. Actual samples were collected from multivitamin tablets and pretreated by the wet digestion method. The Se(IV) concentrations of the samples were determined using an optimized fluorimetric procedure, and the results obtained are summarized in Table 1. The concentrations of Se(IV) in sample 1 determined by the present method are consistent with values obtained by ICP-AES. The Se(IV) concentration using ABDO has been carried out and obtained a tiny deviation of 2% compared with the result detected by ICP-AES. Se(IV) was not detected in the three other samples. Recovery experiments for various amounts of Se(IV) were carried out, and experimental results are also shown in Table 1. The results obtained confirm the validity of the present method. 4. Conclusions In summary, a highly selective and sensitive fluorescent probe for Se(IV) in 5% aqueous ethanol solution was developed. The system is monitored by colorimetric and fluorescence intensity changes. The selectivity of the proposed method for determining Se(IV) was remarkably high, and its detection limit was 2.8 × 10−9 mol L−1 (0.22 g L−1 ). The experimental results suggest that the proposed probe may serve as a foundation of practical fluorescent methods for rapidly determining Se(IV) in actual samples. Acknowledgments We are grateful for financial support from the National Major Scientific Instruments Development Project of china (2011YQ14015001), the Major project of Jilin Province Science and Technology Development plan (20126018, 20130206014GX), the Science and Technology Development Project of Jilin Province of China (No. 201105008), Program for the State Key Laboratory of Inorganic Synthesis and Preparative Chemistry open project (No. 2014-07). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.snb.2013.11.115. References [1] A. Kyriakopolos, D. Behne, R. Physiol, Selenium-containing proteins in mammals and other forms of life, Rev. Physiol. Biochem. Pharmacol. 145 (2002) 1–46. [2] K. Li, S.F.Y. Li, Speciation of selenium and Arsenic compounds in natural waters by capillary zone electrophoresis after on-column preconcentration with fieldamplified injection, Analyst 120 (1995) 361–366. [3] K. Pyrzynska, Analysis of selenium species by capillary electrophoresis, Talanta 55 (2001) 657–667.
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Biographies Guodong Feng is an associate professor in the College of Chemistry at Jilin University major in analytical chemistry. His current research interests are applications of optical sensor. Yanna Dai is studying her masters in the College of Chemistry at Jilin University. She received her B.Sc. in chemistry at Henan University in 2011. Haiyan Jin is a researcher in the College of Chemistry at Jilin University major in analytical chemistry. His current research interests are mass spectrometry. Pengchong Xue is an associate professor in the Department of Organic Chemistry, College of Chemistry at Jilin University. His current research interests are synthesis chemistry. Yanfu Huan is an associate professor in in the College of Chemistry at Jilin University major in analytical chemistry. Her current research interests are molecular recognition, sensors chemistry. Hongyan Shan is a researcher in the college of chemistry at Jilin University major in analytical chemistry. His current research interests are mass spectrometry. Qiang Fei is a lecturer in the College of Chemistry at Jilin University major in analytical chemistry.