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Comparison of Capillary Electrophoresis, HPLC, and Enzyme Immunoassay for Terbuthylazine Detection in Water

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Comparison of Capillary Electrophoresis, HPLC, and Enzyme Immunoassay for Terbuthylazine Detection in Water
  J. Agric. Food Chem. 1995 43, 951-955 951 zyxwvutsrqp Comparison of Capillary Electrophoresis, HPLC nd Enzyme Immunoassay for Terbuthylazine Detection in Water zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Giovanni Dinelli,* Albert0 Vicari, Alessandra Bonetti, and Pietro Catizone Department of Agronomy, University of Bologna, via F. Re 64 0126 Bologna, Italy Tap water and groundwater samples spiked with terbuthylazine were analyzed by capillary electrophoresis (CE), HPLC, and a commercial enzyme immunoassay kit. Over the range of concentrations tested (0.2-2.4 g L-l), the results obtained by the different methods were highly correlated. CE proved to be viable for the detection of terbuthylazine, with good resolution and reproducibility. The detection limit of CE is higher than that of HPLC to detect the lowest concentration of terbuthylazine (0.2 g L-l), but retention times were shorter. Compared to enzyme immunoassay, CE and HPLC needed sample extraction and concentration before analysis but showed higher accuracy and lower variation. Keywords: zyxwvuts erbuthylazine; HPLC; CE; enzyme immunoassay INTRODUCTION Drinking water, surface water, and groundwater pollution by herbicides has stimulated the development of rapid and sensitive methods for the detection of herbicides in water. Terbuthylazine [6-chloro-N-(l,l- dimethylethyl)-N'-ethyl-1,3,5-triazine-2,4-diaminel s an s-triazine herbicide closely related to atrazine. It is not licensed for agricultural use in the United States (Sheperd et al., 1992; teinheimer, 1993) ut is widely used in other countries and has been detected in surface (Hall, 1974; Rossi et al., 19941, ake (Buser, 19901, drinking, and ground waters (Hurle et al., 1987; Meinert and Hafner, 1987; Bowman, 1989). Several methods for the determination of terbuth- ylazine in water have been reported. Usually, high- performance liquid chromatography (HPLC) (Coquart and Hennion, 1991; chlett, 1991; Di Corcia and Mar- chetti, 1992; teinheimer, 1993) nd gas chromatogra- phy (GC) (Meyer et al., 1981; Davi et al., 1992) re used to detect terbuthyladne in water. Recently, capillary electrophoresis (CE) has been reported as a novel approach for the determination of sulfonylurea herbi- cides (Dinelli et al., 1993a,b) nd of s-triazine herbicides in tap and surface waters (Dinelli et al., 1992). Immu- noassays have been used successfully to determine terbuthylazine (Ulrich et al., 1992) nd other s-triazines in water (Bushway et al. 1988; Lucas et al., 1991; Ferguson et al., 1993; awruk et al., 19931, ut they are nonspecific and other s-triazine compounds may react (Thurman et al., 1990; Goh et al., 1991; 992; chneider and Hammock, 1992). Recently, enzyme immunoassay kits have become commercially available in Italy to detect residues of terbuthylazine in water, because atrazine is forbidden since 1989 and was replaced for agriculture purposes by terbuthylazine. Available kits are specific for s-triazines and present high cross- reactivity with terbuthylazine. In this work HPLC was chosen as a reference method to test the reproducibility and accuracy of a commercial immunoassay kit and CE for the detection of terbuthyl- azine in tap and ground waters at the micrograms per liter level. EXPERIMENTAL PROCEDURES Materials. A wettable powder formulation [50 active ingredient (ai)] of terbuthylazine, supplied by Ciba-Geigy Ltd. 0021 8561/95/1443-0951$09.00/0 Basel, Switzerland, was used. Water samples for method comparison were prepared by adding 0, 0.2, 0.8, 1.6 and 2.4 pg L-l of terbuthylazine to duplicate samples of drinking and ground waters. Drinking water was tap water from the municipal water system of Bologna (pH 7.2; hardness, 2.5 g L-l; residue, 0.8 g L-l), whereas groundwater was collected at 1 m depth from lysimeters located at Bologna, near the Department of Agronomy (Rossi Pisa et zy l., 1992). For enzyme immunoassay, additional tap water and groundwater samples were prepared at 0.1, 0.4 and 3.2 pg L- of terbuthylazine. Preliminary results showed that water samples were s-triazine free (data not shown). Furthermore, cross reactivity of im- munoassay with metolachlor, a herbicide oRen used with terbuthylazine, was evaluated using duplicate samples of tap and ground waters at 0.2 and 1.6 ug L-l terbuthylazine soaked with 0, 100, 500, or 1000 pg L-' metolachlor. Reagents for the electrolyte buffer for capillary washing and for the HPLC separation were supplied by Sigma Chemical Co. St. Louis, MO. All solvents, supplied by Bakerbond, were pesticide free. Immunoassay Procedure. The immunoassay analyses of water samples were carried out in 96-well microplates (Envi- roGard Triazine Plate Kit, Millipore Corp., Bedford, MA). The commercial kit is based on the use of polyclonal antibodies that bind both triazines and an atrazine-enzyme conjugate which presents high cross-reactivity o terbuthylazine (Ferguson et al., 1993). The detection limit reported in the kit for terbuthyl- azine in water is 0.06 g L-l. The procedure was similar to that described in the kit. Briefly, 160 pL of each water sample was added to the respective well with 160 pL of atrazine- enzyme conjugate. The wells were mixed with rapid circular motions for 1 min and then incubated at room temperature for 1 h. After incubation, wells were rinsed five times with tap water, and 160 p of substrate was added followed by 80 pL of chromogen. The wells were mixed for 1 min and incubated for 30 min. After incubation, color was fixed with 40 pL of stop solution, mixing the wells until all of the blue color changed to yellow. Samples and standards were analyzed by measuring the relative absorbance AlAo), which is the absorbance at 45 nm observed for a sample A) divided by the absorbance of the negative control Ao). Measurements at 45 nm were made using a microtiter plate reader (Microwell EL301). Calibration Curves by CE and HPLC. A stock solution of the concentration of 1000 mg L- was prepared by dissolving 100 mg of terbuthylazine in 100 mL of methanol. Appropriate dilutions of this stock solution were made in tap water to obtain final concentrations of 1, 2, 4 6, and 8 mg L-I for CE calibration curves and in methanovtap water solution 50150 v/v) to obtain final concentrations of 0.5, 1, 2, 4 6, and 8 mg 1995 American Chemical Society  952 d. Agric. Food Chem. Vol. 43, No. 4, 995 Table 1. Absorbance of Immunoassay as a Function of Terbuthylazine Concentration in Tap Water and Groundwater Samples water sample terbuthylazine zyxwvut g L-l) absorbance Dinelli et al. tap water mean zyxwvuts   En cv zyxwvutsr 96) groundwater mean i Ea cv 96) Standard error zyxwvuts n = 16). 0 0.1 0.2 0.4 0.8 1.6 2.4 3.2 0 0.1 0.2 0.4 0.8 1.6 2.4 3.2 1.206 1.144 1.116 0.940 0.873 0.761 0.613 0.562 0.902 f . 040 4.4 1.084 0.985 0.955 0.910 0.874 0.714 0.634 0.530 0.836 f .114 13.6 L-I for HPLC calibration curves. For each concentration, triplicate injections were made in HPLC or CE. Extraction for CE and HPLC Analysis. Extraction of the ai from the aqueous solutions was performed by a Cle solid- phase extraction (SPE) column (Bakerbond), consisting of 500 mg of CIS (octadecylsilane) resin linked to silica gel with an average 40 m particle size. Prior to analysis, the 1 L samples (tap and ground waters) were filtered through Whatman No. 3 paper. However, preliminary experiments showed that 1 L of sample was not sdXcient to concentrate detectable amounts of terbuthylazine at 0.2 g L-' by CE. Consequently, for this concentration and for CE only the extraction was effected from a 2 L sample. The SPE columns were conditioned with 3 mL of ethyl acetate, followed by 2 mL of methanol and 2 mL of HPLC-grade water; the solvents were run through by gravity drop. Then, 2 mL of HPLC-grade water was added and the sample aspirated by vacuum pump at a flow rate of 25 mL min-I. The column was subsequently vacuum-dried for 10 min and, with the vacuum pump off, was eluted by gravity with an appropriate amount of ethyl acetate. The 0.2 and 0.8 pg L-I samples were concentrated 2000 imes, while the 1.6 and 3.2 g L-' samples were concentrated 1000 imes. All samples were stored at -12 C until analysis. CE Analysis. Separations were performed using micellar electrokinetic capillary chromatography (MECC), by means of the capillary electrophoresis apparatus P/ACE System 2000 (Beckman). Separations were made with a silica-fused capil- lary 50 cm long (from injection point to detector), 75 pm internal diameter (i.d.1, at a costant temperature of 30 zyxwvu   0.2 C. Applied voltage was 25 kV. Detection wavelength was at 214 nm. Samples were injected at a constant pressure of 3.44 x lo3 Pa at the capillary's anode end for 10 s. The electrolyte buffer was 50 mM sodium borate, 22.5 mM sodium dodecyl sulfate, and 10 acetonitrile (v/v), pH 8.0. HPLC Analysis. The HPLC system was a Beckman System Gold 126 with two pumps and a Rheodine valve Model 77254 (20 L oop). The detector was a Beckman diode array Module 168. The column was a reversed-phase Ultrasphere (Beckman, CIS, 25 cm x 4.6 mm i.d., 5 pm particle size). The analyses were performed in isocratic and gradient conditions, because both are reported in the literature for terbuthylazine detection (Galassi zyxwvutsrq t al., 1990; Coquart and Hennion, 1991; Steinheimer, 1993). For the isocratic separations, the mobile phase was methanovwater (60/40 /v) with a 1 mL min-I flow rate, whereas for the gradient separations, the gradient elution was performed by increasing linearly the methanol percentage Table 2. Recovery of Terbuthylazine n Tap Water 1) and Groundwater 2) Samples by Immunoassay, HPLC Gradient Separations, G; Isocratic Separations, I), and CE sample concn (up. L-I) immuno HPLC-G HPLC-I CE % recovery .- 1) Tap Water 0.2 78.6 101.2 93.0 96.8 0.8 95.0 99.5 93.0 104.9 1.6 89.8 96.5 96.5 98.1 2.4 120.1 97.8 93.1 97.4 mean f En 95.8 f .6 98.7 f .4 93.8 f .1 99.3 f .8 (2) Groundwater 0.2 101.1 99.6 105.6 87.5 0.8 78.5 85.0 97.7 97.7 1.6 77.3 93.1 99.1 98.6 2.4 108.3 82.1 89.3 93.3 mean f E 91.3 f .6 89.9 f .2 97.9 f .6 94.3 2.5 a Standard error n = 8) from 50 to 70 in 20 min. An injection volume of 20 pL and UV detection at 220 nm were used. RESULTS AND DISCUSSION Standard Curves by Immunoassay. For tap water samples, a linear relationship between the natural logarithm of terbuthylazine concentration, in the range of 0.1-3.2 pg L-l, and the relative absorbance AlAo) was found. The regression equation was y = 0.67 0.13 In x r2 = 0.9751, where x is the terbuthylazine concen- tration and y is AlAo. By contrast, the equation that best related terbuthylazine concentration in groundwa- ter to AIAo was a second-order polynomial r = 0.74 0.16 In x 4.13 In x2, r2 = 0.988). The two equations were employed to assign a concentration value to spiked tap water and groundwater samples, respectively. Table 1 shows that the coefficient of variation (CV) was significantly higher in groundwater than in tap water, suggesting that some matrix effect was present in the groundwater, and this may cause a less accurate detec- tion of terbuthylazine, especially at low concentrations. The presence of chemical interferences is suggested by lower absorbances in blanks (-lO.l , Table 1) com- pared to tap water blanks. Standard Curves by CE and HPLC. The calibra- tion curves for CE quantitative determinations showed a linear instrumental response of the capillary-injected terbuthylazine in the 30-480 pg range, which matched the 10 s (60 nL) injection of standards with concentra- tion in the range of 0.5-8 mg L-l. The regression equation was y = 0.065~ r2 = 0.995), where y is the peak area and x is the concentration of the active ingredient (ai) in milligrams per milliliter. The calibration curves for quantitative determination by isocratic and gradient HPLC separations showed linear responses in the 10-160 ng range of the injected terbuthylazine. These concentrations match the 20 pL injection of standard with concentrations from 0.5 to 8 mg L-' ai. Regression equations obtained by isocratic and gradient separations were y = 3.52~ r2 = 0.997) and y = 3.5lx r2 = 0.9981, respectively. Determination of Terbuthylazine. Good recover- ies were obtained for all methods tested (Table 2). The average recoveries by HPLC and CE were not different from those obtained by immunoassay. However, the mean coefficients of variation for immunoassay in tap water and in groundwater were 22.7% and 33.5%,  CE, HPLC, and Immunoassay Detection of Terbuthylazine zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCB . Agric. Food Chem. Vol. 43, No. 4 1995 953 zyxwvutsrqp  f zyxw  h a> I I 0 5 10 15 b> zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA  \ 0 02 a u I 1 1 .*-._._...... -.-- 0 4 a 2 I 1 5 10 Time <mid Figure 1. zyxwvutsrqpon erbuthylazine detection in groundwater samples spiked at 0.2 u L-l by (a) HPLC in gradient conditions, (b) HPLC in isocratic conditions, and (c) CE. The arrows ndicate the terbuthylazine peak (au = absorbance unit). The chemical structure of terbuthylazine is also reported. respectively, while the mean coefficients of variation for The different positions of the matrix interferences in the instrumental determinations were in all cases less HPLC and in CE analysis, in advance and next to the than 9% (data not shown). This indicates that the ai peak, respectively, are shown in Figure 1. CE showed accuracy and precision of the immunoassay determina- an on-column purification effect, as demonstrated by the tion over the range of concentration tested were lower higher percent area of the terbuthylazine peak in CE than those obtained for HPLC and CE, especially in (20%) han that observed in HPLC (5 ) with respect to groundwater samples. the total compounds detected. This suggests an on-  954 J. Agric. food Chem. Vol. 43, No. 4, 1995 Table 3. Effect of Increasing Rates of Metolachlor zyxwv n Water on Terbuthylazine Detection by Immunoassay Dinelli et al. zyxwvutsrqp spiked terbuthylazine + terbuthylazine detected (ug L- ) metolachlor (ug L-l) tap water groundwater 0.20 0 0.16 0.29 0.20 100 0.19 0.67 0.20 500 0.20 1.00 0.20 1000 0.28 0.87 mean zyxwvutsr   Ea 0.21 zyxwvuts   .03 0.71 f .13 1.60 0 1.36 1.60 1.60 100 1.61 1.63 1.60 + 500 1.29 1.56 1.60 + 1000 1.07 2.02 mean Ea 1.33 .14 1.70 f .13 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA a Standard error n = 8). Table 4. Correlation Parameters Coefficient of Correlation, Slope, and Intercept, zyxwvu   = 8 among Methods HPLC-G, Gradient Separations; HPLC-I, Isocratic Separations) methods Ra slope f Eb intercept 1) Tap Water HPLC-G vs CE 0.994*** 0.990 f .043 0.024 HPLC-I vs CE 0.996*** 1.028 f .036 0.025 HPLC-G vs immuno 0.975*** 1.241 f .113 - 0.209 HPLC-I vs immuno 0.967*** 1.275 f .137 0.191 (2) Groundwater HPLC-G vs HPLC-I 0.992*** 1.073 f .052 0.015 HPLC-G vs CE 0.995*** 1.133 f .044 0.035 HPLC-I vs CE 0.989*** 1.042 f .062 0.037 HPLC-G vs HPLC-I 0.997*** 0.963 f .027 0.006 CE vs immuno 0.963*** 1.231 f .139 -0.211 HPLC-G vs immuno 0.915** 1.261 f .226 0.202 HPLC-I vs immuno 0.905** 1.154 f .221 0.195 CE vs immuno 0.916** 1.108 f .198 0.156 ***, significant at P 0.001; **, significant at P 0.01. column exclusion of some interference compounds dur- ing the CE separation. Furthermore, CE separation (Figure IC) s more rapid than HPLC. In isocratic and gradient conditions, HPLC retention times of terbuthyl- azine were 10.25 f .15 and 13.01 f .08 min, respec- tively, while in CE it was 5.37 k .07 min. In spite of apparent values up to 3.4-fold higher than the spiked level of terbuthylazine, analysis of variance revealed that increasing metolachlor concentration from 0 to 1000 pug L-l had no significant effect on the determination of terbuthylazine with immunoassay at 0.2 and 1.6 pg L-l in tap water and groundwater (Table 3). However, terbuthylazine determination was signifi- cantly overestimated in groundwater at 0.2 pg L-l, probably as an effect of the lower accuracy of immu- noassay for groundwater samples at lower concentra- tions. Correlation Among Methods. Regression analysis yielded coefficients of correlation R) etween the im- munoassay and the instrumental determinations (HPLC and CE) in tap water and groundwater significant at P < 0.001 and P < 0.01 respectively, while the coefficients of correlation between CE and HPLC were all highly significant at P < 0.001 (Table 4). These results confirm the lower accuracy of immunoassay for terbuthylazine determination in groundwater samples. The slope of the regression lines correlating HPLC and CE, for tap and ground waters, was not greater than 1, and the intercepts were not different from 0, demonstrating that HPLC and CE were correlated near the theoretical optimum value. In contrast, the slope of the regression Mean f tandard error. lines for the correlation between instrumental methods and immunoassay was greater than 1 and the intercepts were not different from 0. This indicates that the immunoassay kit overestimates the dose of terbuthyl- azine. Conclusion. The present data confirm the viability of CE in the detection and quantitation of terbuthyla- zine in water at micrograms per liter levels. CE shows potential advantages over HPLC, such as shorter reten- tion times and a related interesting cost-benefit analy- sis, due to low consumption of solvents in CE too. However, CE has a higher detection limit than HPLC, because CE requires a volume of injection in the nanoliter order. In general, CE application on a routine scale for the analysis of herbicides is restricted by the relatively fewer developed methods and literature sources on CE, mainly due to the much shorter history of CE with respect to the other chromatographic techniques. The immunoassay kit for the detection of terbuthyl- azine offers many advantages over chromatographic procedures (HPLC and CE) used to detect and quanti- tate the ai in water at micrograms per liter level. These advantages include the speed of analysis, the high number of samples that can be processed in a day, and time reductions in sample preparation and cleanup procedures. In effect, our data show that mean recover- ies from immunoassay are comparable to those obtained by HPLC and CE, that immunoassay and instrumental determinations are well correlated, and that meto- lachlor, a herbicide often used with terbuthylazine, has a negligible cross-reactivity with the immunoassay. However, immunoassay is less precise and accurate than HPLC and CE, especially in groundwater, but has a great potential as a rapid screening qualitative test prior to accurate HPLC or CE measurements. Great attention has to be paid when this kit is applied to basin- and territorial-scale researches, where other s-triazines or terbuthylazine metabolites may cross- react with immunoassay. ACKNOWLEDGMENT We thank Prof. Robert Zimdahl (Colorado State University, Fort Collins, CO) and Prof. Guido C. Galletti (University of Reggio Calabria, Italy) for useful sugges- tions. We also thank Dr. Antonia Gorbanova (Univer- sity of Plovdiv, Bulgaria) for assistance in the analyses. LITERATURE CITED Bowman, B. T. Mobility and persistence of the herbicide atrazine, metolachlor and terbuthylazine in Plainfield sand using field lysimeters. Environ. Toxicol. Chem. 1989, , 485-491. Buser, H. R. Atrazine and other s-triazine herbicides in lakes and in rain in Switzerland. Environ. Sci. Technol. 1990,24, 1049-1058. Bushway, R. J.; Perkins, B.; Savage, S. A.; Lekousi, S. J.; Ferguson, B. S. Determination of atrazine residues in water and soil by enzyme immunoassay. Bull. Environ. Contam. Toxicol. 1988, 0, 47-654. Coquart, V.; ennion, M.4. Determination of chlorotriazines in aqueous environmental samples at the ng/L level using preconcentration with a cation exchanger and on-line high- performance liquid chromatography. J. Chromatogr. 1991, 585, 67-73. Dad, L. M.; Baldi, M.; Penazzi, L.; Liboni, M. Evaluation of the membrane approach to solid-phase extractions of pes- ticide residues in drinking water. Pestic. Sei. 1992,35, 3- 67.  CE, HPLC, and Immunoassay Detection of Terbuthylazine zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Di Corcia, A.; Marchetti, M. Method development for monitor- ing pesticides in environmental waters: liquid-solid extrac- tion followed by liquid chromatography. zyxwvuts nviron. Sci. Technol. 1992,26, 66-74. Dinelli, G.; Vicari, A.; Bonetti, A.; Catizone, P. Preliminary results on the use of capillary electrophoresis for detection of herbicides in water. Proceedings, V International Sym- posium “Biotecnologie, Analitiche di Laboratorio”, Riva del Garda, Oct 25-28, 1992; Landi, E., Piccolo, A., Dumontet, S., Eds.; Ordine Nazionale dei Biologi: Roma, Italy, 1992; Vol. 1, pp 269-279. Dinelli, G.; Vicari, A.; Catizone, P. Use of capillary electro- phoresis for detection of metsulfuron and chlorsulfuron in tap water. J. Agric. Food Chem. 1993a, 41, 742-746. Dinelli, G.; Vicari, A.; Bonetti, A.; Catizone, P. Triasulfuron, chlorsulfuron and metsulfuron hydrolysis and triasulfuron degradation in soil. Proceedings, zyxwvut X Symposium on Pesticide Chemistry “Mobility and degradation zyxwvuts f xenobiotics”, Pi- acenza, Oct 12-13; Del Re, A. M., Capri, E., Evans, s. p., Natali, P., Trevisan, M., Eds.; Edizioni Biagini: Lucca, Italy, 1993b; pp 411-420. EEC. Directive relating to the quality of water intended for human consumption. zyxwvut R J. Eur. Community 1980, 23, (Aug), L229/1130 (80/778/EEC). Ferguson, B. S.; Kelsey, D. E.; Fan, T. S.; Bushway, R. J. Pesticide testing by enzyme immunoassay at trace levels in environmental and agricultural samples. Sci. Total Environ. 1993, 132, 415-428. Galassi, S.; Boniardi, N.; De Paolis, A. Multireside methods for the analysis of herbicides in water. Boll. Chim. Igien. 1990,41,405-413. Goh, K. S.; Hernandez, J.; Powell, S. J.; Garretson, C.; Troiano, J.; Ray, M.; Greene, C. D. Enzyme immunoassay for the determination of atrazine residues in soil. Bull. Environ. Contam. Toxicol. 1991,45, 208-214. Goh, K. S.; Richman, S. J.; Troiano, J.; Garretson, C. L.; Hernandez, J.; Hsu, J.; White, J.; Barry, T. A.; Ray, M.; Tran, D.; Miller, N. K. ELISA of simazine in soil: applica- tions for a field leaching study. Bull. Environ. Contam. Toxicol. 1992, 48 554-560. Hall, J. K. Erosional losses of s-triazine herbicides. J. Environ. Qual. 1974,3, 174-180. Hurle, K.; Giessl, H.; Kirchoff, J. Occurrence of some selected pesticides in groundwater. Schr. zyxwvutsr er. Wasser 1987,68,169- 190. Lawruk, T. S.; Lachman, C. E.; Jourdan, S. W.; Fleeker, J. R.; Herzog, D. P.; Rubio, F. M. Quantification of cyanazine in water and soil by a magnetic particle-based ELISA. J. Agric. Food Chem. 1993,41, 747-752. J. Agric. Food Chem. Vol. 43, No. 4, 995 955 Lucas, A,; Schneider, P.; Harrison, R. 0.; Seiber, J. N.; Hammock, B. D.; Biggar, J.W.; Rolston, D. E. Determination of atrazine and simazine in water and soil using polyclonal and monoclonal antibodies in enzyme-linked immunosor- bent assay. Food Agric. Immunol. 1991,3, 155-167. Meinert, G.; Hafner, M. Possibilities and problems with the application of agrochemicals in protected water zones. Schr. Ver. Wasser 1987, 68, 51-63. Meyer, J.; Novak, K.; Suter, R.; Tomann, A.; Bosshardt, H. P. Gas-liquid chromatographic determination of terbuthylazine technical and its formulations: collaborative studies. J. Assoc. Off. Anal. Chem. 1981, 64, 825-828. Rossi Pisa, P.; Bertozzi, R.; Ventura, F.; Maini, P. Herbicide groundwater pollution in lysimeters with soybean and wheat. Riv. Agron. 1992,26, 690-696. Rossi Pisa, P.; Vicari, A.; Catizone, P. Effect of barley Hor- deum vulgare L.) cover crop on soil and runoff losses. Riv. Agron. 1994,28, 384-391. Schlett, C. Multi-residue analysis of pesticides by HPLC after solid phase extraction. Fresenius’ J. Anal. Chem. 1991,339, 344-347. Schneider, P.; Hammock, B. D. Influence of the ELISA format and the hapten-enzyme conjugate on the sensitivity of an immunoassay for s-triazine herbicides using monoclonal antibodies. J. Agric. Food Chem. 1992, 40, 525-530. Sheperd, T. R.; Carr, J. D.; Duncan, D.; Pederson, D. T. C18 extraction of atrazine from small water sample volumes. J. Assoc. Off. nal. Chem. 1992, 75, 581-583. Steinheimer, T. R. HPLC determination of atrazine and principal degradates in agricultural soils and associated surface and ground water. J. Agric. Food Chem. 1993,41, 588-595. Thurman, E. M.; Meyer, M.; Pomes, M.; Perry, C. A.; Schwab, A. P. Enzyme-linked immunosorbent assay compared with gas chromatography/mass spectrometry for the determina- tion of triazine herbicides in water. Anal. Chem. 1990, 62, Ulrich, P.; Weil, L.; Niessner, R. Rapid fluorescence immu- noassay (FIA) for the determination of terbuthylazine. Fresenius’ J. Anal. Chem. 1992, 343, 50-51. Received for review April 14, 1994. Revised manuscript received November 15, 1994. Accepted January 27, 1995.@ This work was financed by European Economic Community, Contract EEC AIR3-ST92002. ‘ 2043-2048. JF940192F Abstract published zyx n Advance ACS Abstracts, March 1, 1995.
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