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Determination of triazine herbicide residues in water samples by on-line sweeping concentration in micellar electrokinetic chromatography
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Chinese Chemical Letters 19 (2008) 1487–1490 www.elsevier.com/locate/cclet
Determination of triazine herbicide residues in water samples by on-line sweeping concentration in micellar electrokinetic chromatography Shuai Hua Zhang, Yuan Yuan Yang, Dan Dan Han, Chun Wang, Xin Zhou, Xiao Huan Zang, Zhi Wang * Key Laboratory of Bioinorganic Chemistry, College of Sciences, Agricultural University of Hebei, Baoding 071001, China Received 11 June 2008
Abstract A new method for the determination of atrazine, simazine and prometryn in water samples by on-line sweeping concentration technique in micellar electrokinetic chromatography (MEKC) was developed. Various parameters affecting sample enrichment and separation efficiency were systematically studied. Compared with the conventional MEKC method, up to 60–200-fold improvement in concentration sensitivity was achieved in terms of peak height by using this sweeping injection technique. The compound strychnine was used as the internal standard for the improvement of the experimental reproducibility. The limits of detection (S/ N = 3:1) for atrazine, simazine and prometryn were 9, 10 and 0.5 ng mL 1, respectively. This method has been successfully applied to the analysis of atrazine, simazine and prometryn in lake, steam and ground water. # 2008 Zhi Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Triazine herbicides; On-line concentration; MEKC; Sweeping; Water samples
Triazines are important selective pre- and post-emergence herbicides used widely for the control of weeds in many agricultural crops like corn, wheat, maize and barley. Because of their widespread use, weak adsorptivity, high persistence and toxicity, triazine herbicides can contaminate the aquatic environment through agricultural run-off and leaching. Atrazine, simazine and prometryn are the main important triazines regularly found in water samples [1]. According to the European Union directive [2], the maximum residue limit (MRL) for each herbicide in water is 0.5 mg L 1. Capillary electrophoresis (CE) has been demonstrated to be a fast, powerful and highly efficient technique for some routine applications, as in biological, environmental, pharmaceutical and toxicological areas [3]. However, the main drawback of CE is the poor concentration sensitivity for the most commonly used UV detection. To surmount this problem, several on-line concentration procedures have been explored [3–7]. Sweeping, firstly developed by Quirino and Terabe [6] in 1998, is an effective on-line sample concentration technique in micellar electrokinetic chromatography (MEKC). In continuation for our previous endeavors in on-line concentration technique of CE [8–11], here in, we reported a new on-line sweeping MEKC method for the analysis of atrazine, simazine and prometryn in water samples. * Corresponding author. E-mail address: [email protected] (Z. Wang). 1001-8417/$ – see front matter # 2008 Zhi Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.09.017
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S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
1. Experimental All capillary electrophoresis experiments were carried out on a Beckman CE System (Model P/ACE MDQ, Fullerton, CA, USA), equipped with a DAD detector. CE was performed in an uncoated fused-silica capillary (i.d. 75 mm, total and effective lengths were 50 and 40 cm, respectively). To ensure repeatability, the capillary was flushed between consecutive analyses with 0.1 mol L 1 HCl (3 min), doubly distilled water (2 min) and finally with the background solution (BGS) (5 min). The optimal conditions for the experiment were as follows: BGS was 50 mmol L 1 H3PO4 (pH 2.5) containing 15% methanol and 100 mmol L 1 SDS with an applied voltage of 20 kVat 25 8C. Sample injection was performed at 1.0 psi for 60 s with diode array detection at 220 nm. A mixture stock solution containing each of atrazine, simazine and prometryn at 10 mg mL 1 was prepared in 100 mmol L 1 H3PO4 (pH 2.5). Strychnine was used as the internal standard, and its stock solution was prepared at 100 mg mL 1 in 100 mmol L 1 H3PO4 (pH 2.5). Water samples from Longtanxia steam, Xidayang Lake and ground water in Baoding were analysed with the proposed method. All water samples were filtered through 0.45-mm polyamide filter to remove suspended particles before use. 100 mL 1.0 mol L 1 H3PO4 (pH 2.5) and 50 mL 10 mg mL 1 of the internal standard strychnine were added to 850 mL of water samples in glass tube prior to use, to get a similar conductivity to the BGS.
2. Results and discussion Sweeping is an on-line sample concentration technique in MEKC. It occurs when the sample matrix is prepared in a buffer solution with conductivity that is similar or higher than BGS and without adding pseudostationary phase (micelles). When charged micelles in BGS penetrates the sample zone during the application of voltage, picking or accumulating of the analytes occur due to partitioning or interaction of analytes with micelles. Therefore, the analyte zones are narrowed due to a partitioning mechanism as the sample molecules are sorbed into the micelles phase [3]. In order to obtain the best separation efficiency and on-line sweeping focusing effect, the experimental conditions of buffer concentration, buffer pH, SDS concentration, organic solvent content and injection time were optimized. As a result, the optimal experimental conditions were 50 mmol L 1 H3PO4 at pH 2.5 as BGS, methanol concentration at 15%, SDS concentration at 100 mmol L 1, applied separation voltage at 20 kV and injection at 1.0 psi for 60 s. The sensitivity enhancement factor (SEFheight) in terms of peak height can be calculated by simply getting the ratio of the peak heights obtained by sweeping and normal injection (0.5 psi, 5 s) method and then multiplying the ratio with the dilution factor. Under the above optimized experimental conditions, around 200-fold sensitivity enhancement was achieved for prometryn, and 60-fold for atrazine and simazine (Fig. 1).
Fig. 1. Separation of triazines by conventional MEKC (a) and sweeping MEKC (b). BGS: 50 mmol L 1 H3PO4 (pH 2.5), 100 mmol L 1 SDS, 15% methanol. (a) 10 mg mL 1 of the standard mixture stock solution in BGS, injection for 5 s at 0.5 psi; (b) 0.5 mg mL 1 in 100 mmol L 1 H3PO4 (pH 2.5), injection for 60 s at 1.0 psi; detection, 220 nm; applied voltage, 20 kV. Other conditions are given in Section 1. (1) Prometryn, (2) strychnine (0.5 mg mL 1), (3) atrazine and (4) simazine.
S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
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Table 1 The linear equations and LODs (S/N = 3) of atrazine, simazine and prometryn.
The linear equation Calibration curve (mg mL 1) Coefficient of variation (R2) LOD (ng mL 1)
Atrazine
Simazine
Prometryn
Y = 0.1317 + 0.3965X 0.05–5 0.995 9
Y = 0.1787 + 0.4629X 0.05–5 0.995 10
Y = 0.1277 + 0.2209X 0.005–0.5 0.997 0.5
A series of standard solutions in 100 mmol L 1 H3PO4 (pH 2.5) containing atrazine, simazine and prometryn were made to obtain the final concentration of each at 0.005, 0.05, 0.2, 0.4, 0.5, 2.0, 4.0 and 5.0 mg mL 1 with the internal standard (strychnine, at 0.5 mg mL 1) for the establishment of the calibration graph. The ratios of the peak area of the analytes to the internal standard strychnine were used for quantification signals as ordinate (Y) and the concentration of the analytes in mg mL 1 as abscissa (X). Table 1 gives the data of the linear equations and LODs (S/N = 3) for the three analytes. The limits of detection (LODs) for prometryn, atrazine and simazine were 0.5 ng mL 1, 9 ng L 1 and 10 ng mL 1, respectively. For the run-to-run reproducibility studies, five parallel determinations were made at the concentration of 0.1 mg mL 1. As a result, the relative standard deviations (R.S.D.s) in terms of migration times were quite reproducible, within 1.2% for atrazine, 1.3% for simazine and 1.1% for prometryn and the R.S.D.s in terms of peak area ratio were 2.2%, 2.5% and 3.2% for atrazine, simazine and prometryn, respectively. The typical electropherograms of steam, lake and ground water samples were shown in Fig. 2. No triazines investigated were found in Xidayang Lake and ground water at quantifiable level. Only prometryn residue was found in Longtanxia steam water at a concentration of 0.9 ng mL 1. The recoveries of atrazine, simazine and prometryn in the water samples were measured by adding 0.1 mg mL 1 of the mixture standard solutions into the samples, then measuring the content of each analytes by the same procedures stated above. The results are summarized in Table 2.
Fig. 2. Electropherograms of Longtanxia steam. (a) Longtanxia steam sample (0.5 mg mL 1 strychnine), (b) Longtanxia steam sample spiked with 50 ng mL 1 of triazines. (1) Prometryn, (2) strychnine (0.5 mg mL 1), (3) atrazine and (4) simazine.
Table 2 The average recoveries of atrazine, simazine and prometryn in water samples. Samples
Longtanxia steam Xidayang Lake Ground water
Average recovery (%)
R.S.D.s (%)
Atrazine
Simazine
Prometryn
Atrazine
Simazine
Prometryn
94.3 87.2 87.5
88.1 86.3 86.2
83.7 94.6 88.2
5.0 5.6 6.3
2.8 2.4 6.0
4.3 3.3 4.8
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S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
3. Conclusion An on-line sweeping MEKC method for the determination of atrazine, simazine and prometryn in steam, lake and ground water has been developed. The three triazines can be resolved within 6 min. Compared with the conventional MEKC method, up to 60–200-fold improvement in concentration sensitivity was achieved by using this on-line sweeping preconcentration method. The proposed method was successfully applied to water samples with satisfactory results. Acknowledgments This project is sponsored by the Natural Science Foundation of Hebei (Nos. B2006000413, B2008000210). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
R. Loos, R. Niessner, J. Chromatogr. A 835 (1999) 217. EC Drinking water Guideline 98/83/EC, Brussels, November 1998. S.L. Simpson Jr., J.P. Quirino, S. Terabe, J. Chromatogr. A 1184 (2008) 504. Z.K. Shihabi, Electrophoresis 23 (2003) 1612. P. Britz-McKibbin, D.D.Y. Chen, Anal. Chem. 72 (2000) 1242. J.P. Quirino, S. Terabe, Science 282 (1998) 465. J.P. Quirino, J.B. Kim, S. Terabe, J. Chromatogr. A 965 (2002) 357. C. Wang, C.R. Li, X.H. Zang, D.D. Han, Z.M. Liu, Z. Wang, J. Chromatogr. A 1143 (2007) 270. C. Wang, D.D. Han, Z. Wang, X.H. Zang, Q.H. Wu, Anal. Chim. Acta 572 (2006) 190. D.D. Han, C. Wang, Z. Wang, Q.H. Wu, X.H. Zang, Chin. Chem. Lett. 17 (2006) 953. X.H. Zang, C.R. Li, Q.H. Wu, C. Wang, D.D. Han, Z. Wang, Chin. Chem. Lett. 18 (2007) 316.
Chinese Chemical Letters 19 (2008) 1487–1490 www.elsevier.com/locate/cclet
Determination of triazine herbicide residues in water samples by on-line sweeping concentration in micellar electrokinetic chromatography Shuai Hua Zhang, Yuan Yuan Yang, Dan Dan Han, Chun Wang, Xin Zhou, Xiao Huan Zang, Zhi Wang * Key Laboratory of Bioinorganic Chemistry, College of Sciences, Agricultural University of Hebei, Baoding 071001, China Received 11 June 2008
Abstract A new method for the determination of atrazine, simazine and prometryn in water samples by on-line sweeping concentration technique in micellar electrokinetic chromatography (MEKC) was developed. Various parameters affecting sample enrichment and separation efficiency were systematically studied. Compared with the conventional MEKC method, up to 60–200-fold improvement in concentration sensitivity was achieved in terms of peak height by using this sweeping injection technique. The compound strychnine was used as the internal standard for the improvement of the experimental reproducibility. The limits of detection (S/ N = 3:1) for atrazine, simazine and prometryn were 9, 10 and 0.5 ng mL 1, respectively. This method has been successfully applied to the analysis of atrazine, simazine and prometryn in lake, steam and ground water. # 2008 Zhi Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Triazine herbicides; On-line concentration; MEKC; Sweeping; Water samples
Triazines are important selective pre- and post-emergence herbicides used widely for the control of weeds in many agricultural crops like corn, wheat, maize and barley. Because of their widespread use, weak adsorptivity, high persistence and toxicity, triazine herbicides can contaminate the aquatic environment through agricultural run-off and leaching. Atrazine, simazine and prometryn are the main important triazines regularly found in water samples [1]. According to the European Union directive [2], the maximum residue limit (MRL) for each herbicide in water is 0.5 mg L 1. Capillary electrophoresis (CE) has been demonstrated to be a fast, powerful and highly efficient technique for some routine applications, as in biological, environmental, pharmaceutical and toxicological areas [3]. However, the main drawback of CE is the poor concentration sensitivity for the most commonly used UV detection. To surmount this problem, several on-line concentration procedures have been explored [3–7]. Sweeping, firstly developed by Quirino and Terabe [6] in 1998, is an effective on-line sample concentration technique in micellar electrokinetic chromatography (MEKC). In continuation for our previous endeavors in on-line concentration technique of CE [8–11], here in, we reported a new on-line sweeping MEKC method for the analysis of atrazine, simazine and prometryn in water samples. * Corresponding author. E-mail address: [email protected] (Z. Wang). 1001-8417/$ – see front matter # 2008 Zhi Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2008.09.017
1488
S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
1. Experimental All capillary electrophoresis experiments were carried out on a Beckman CE System (Model P/ACE MDQ, Fullerton, CA, USA), equipped with a DAD detector. CE was performed in an uncoated fused-silica capillary (i.d. 75 mm, total and effective lengths were 50 and 40 cm, respectively). To ensure repeatability, the capillary was flushed between consecutive analyses with 0.1 mol L 1 HCl (3 min), doubly distilled water (2 min) and finally with the background solution (BGS) (5 min). The optimal conditions for the experiment were as follows: BGS was 50 mmol L 1 H3PO4 (pH 2.5) containing 15% methanol and 100 mmol L 1 SDS with an applied voltage of 20 kVat 25 8C. Sample injection was performed at 1.0 psi for 60 s with diode array detection at 220 nm. A mixture stock solution containing each of atrazine, simazine and prometryn at 10 mg mL 1 was prepared in 100 mmol L 1 H3PO4 (pH 2.5). Strychnine was used as the internal standard, and its stock solution was prepared at 100 mg mL 1 in 100 mmol L 1 H3PO4 (pH 2.5). Water samples from Longtanxia steam, Xidayang Lake and ground water in Baoding were analysed with the proposed method. All water samples were filtered through 0.45-mm polyamide filter to remove suspended particles before use. 100 mL 1.0 mol L 1 H3PO4 (pH 2.5) and 50 mL 10 mg mL 1 of the internal standard strychnine were added to 850 mL of water samples in glass tube prior to use, to get a similar conductivity to the BGS.
2. Results and discussion Sweeping is an on-line sample concentration technique in MEKC. It occurs when the sample matrix is prepared in a buffer solution with conductivity that is similar or higher than BGS and without adding pseudostationary phase (micelles). When charged micelles in BGS penetrates the sample zone during the application of voltage, picking or accumulating of the analytes occur due to partitioning or interaction of analytes with micelles. Therefore, the analyte zones are narrowed due to a partitioning mechanism as the sample molecules are sorbed into the micelles phase [3]. In order to obtain the best separation efficiency and on-line sweeping focusing effect, the experimental conditions of buffer concentration, buffer pH, SDS concentration, organic solvent content and injection time were optimized. As a result, the optimal experimental conditions were 50 mmol L 1 H3PO4 at pH 2.5 as BGS, methanol concentration at 15%, SDS concentration at 100 mmol L 1, applied separation voltage at 20 kV and injection at 1.0 psi for 60 s. The sensitivity enhancement factor (SEFheight) in terms of peak height can be calculated by simply getting the ratio of the peak heights obtained by sweeping and normal injection (0.5 psi, 5 s) method and then multiplying the ratio with the dilution factor. Under the above optimized experimental conditions, around 200-fold sensitivity enhancement was achieved for prometryn, and 60-fold for atrazine and simazine (Fig. 1).
Fig. 1. Separation of triazines by conventional MEKC (a) and sweeping MEKC (b). BGS: 50 mmol L 1 H3PO4 (pH 2.5), 100 mmol L 1 SDS, 15% methanol. (a) 10 mg mL 1 of the standard mixture stock solution in BGS, injection for 5 s at 0.5 psi; (b) 0.5 mg mL 1 in 100 mmol L 1 H3PO4 (pH 2.5), injection for 60 s at 1.0 psi; detection, 220 nm; applied voltage, 20 kV. Other conditions are given in Section 1. (1) Prometryn, (2) strychnine (0.5 mg mL 1), (3) atrazine and (4) simazine.
S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
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Table 1 The linear equations and LODs (S/N = 3) of atrazine, simazine and prometryn.
The linear equation Calibration curve (mg mL 1) Coefficient of variation (R2) LOD (ng mL 1)
Atrazine
Simazine
Prometryn
Y = 0.1317 + 0.3965X 0.05–5 0.995 9
Y = 0.1787 + 0.4629X 0.05–5 0.995 10
Y = 0.1277 + 0.2209X 0.005–0.5 0.997 0.5
A series of standard solutions in 100 mmol L 1 H3PO4 (pH 2.5) containing atrazine, simazine and prometryn were made to obtain the final concentration of each at 0.005, 0.05, 0.2, 0.4, 0.5, 2.0, 4.0 and 5.0 mg mL 1 with the internal standard (strychnine, at 0.5 mg mL 1) for the establishment of the calibration graph. The ratios of the peak area of the analytes to the internal standard strychnine were used for quantification signals as ordinate (Y) and the concentration of the analytes in mg mL 1 as abscissa (X). Table 1 gives the data of the linear equations and LODs (S/N = 3) for the three analytes. The limits of detection (LODs) for prometryn, atrazine and simazine were 0.5 ng mL 1, 9 ng L 1 and 10 ng mL 1, respectively. For the run-to-run reproducibility studies, five parallel determinations were made at the concentration of 0.1 mg mL 1. As a result, the relative standard deviations (R.S.D.s) in terms of migration times were quite reproducible, within 1.2% for atrazine, 1.3% for simazine and 1.1% for prometryn and the R.S.D.s in terms of peak area ratio were 2.2%, 2.5% and 3.2% for atrazine, simazine and prometryn, respectively. The typical electropherograms of steam, lake and ground water samples were shown in Fig. 2. No triazines investigated were found in Xidayang Lake and ground water at quantifiable level. Only prometryn residue was found in Longtanxia steam water at a concentration of 0.9 ng mL 1. The recoveries of atrazine, simazine and prometryn in the water samples were measured by adding 0.1 mg mL 1 of the mixture standard solutions into the samples, then measuring the content of each analytes by the same procedures stated above. The results are summarized in Table 2.
Fig. 2. Electropherograms of Longtanxia steam. (a) Longtanxia steam sample (0.5 mg mL 1 strychnine), (b) Longtanxia steam sample spiked with 50 ng mL 1 of triazines. (1) Prometryn, (2) strychnine (0.5 mg mL 1), (3) atrazine and (4) simazine.
Table 2 The average recoveries of atrazine, simazine and prometryn in water samples. Samples
Longtanxia steam Xidayang Lake Ground water
Average recovery (%)
R.S.D.s (%)
Atrazine
Simazine
Prometryn
Atrazine
Simazine
Prometryn
94.3 87.2 87.5
88.1 86.3 86.2
83.7 94.6 88.2
5.0 5.6 6.3
2.8 2.4 6.0
4.3 3.3 4.8
1490
S.H. Zhang et al. / Chinese Chemical Letters 19 (2008) 1487–1490
3. Conclusion An on-line sweeping MEKC method for the determination of atrazine, simazine and prometryn in steam, lake and ground water has been developed. The three triazines can be resolved within 6 min. Compared with the conventional MEKC method, up to 60–200-fold improvement in concentration sensitivity was achieved by using this on-line sweeping preconcentration method. The proposed method was successfully applied to water samples with satisfactory results. Acknowledgments This project is sponsored by the Natural Science Foundation of Hebei (Nos. B2006000413, B2008000210). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
R. Loos, R. Niessner, J. Chromatogr. A 835 (1999) 217. EC Drinking water Guideline 98/83/EC, Brussels, November 1998. S.L. Simpson Jr., J.P. Quirino, S. Terabe, J. Chromatogr. A 1184 (2008) 504. Z.K. Shihabi, Electrophoresis 23 (2003) 1612. P. Britz-McKibbin, D.D.Y. Chen, Anal. Chem. 72 (2000) 1242. J.P. Quirino, S. Terabe, Science 282 (1998) 465. J.P. Quirino, J.B. Kim, S. Terabe, J. Chromatogr. A 965 (2002) 357. C. Wang, C.R. Li, X.H. Zang, D.D. Han, Z.M. Liu, Z. Wang, J. Chromatogr. A 1143 (2007) 270. C. Wang, D.D. Han, Z. Wang, X.H. Zang, Q.H. Wu, Anal. Chim. Acta 572 (2006) 190. D.D. Han, C. Wang, Z. Wang, Q.H. Wu, X.H. Zang, Chin. Chem. Lett. 17 (2006) 953. X.H. Zang, C.R. Li, Q.H. Wu, C. Wang, D.D. Han, Z. Wang, Chin. Chem. Lett. 18 (2007) 316.