Environ. Sci. Technol. 1996, 30, 3259-3265
Solid-Phase Microextraction of Nitrogen- and Phosphorus-Containing Pesticides from Water and Gas Chromatographic Analysis TARUN K. CHOUDHURY, KLAUS O. GERHARDT, AND THOMAS P. MAWHINNEY* Experiment Station Chemical Laboratories, Room 4, Agriculture Building, College of Agriculture, Food and Natural Resources, University of MissourisColumbia, Columbia, Missouri 65211
Solid-phase microextraction (SPME), a single-step solvent-free extraction, followed by gas-liquid chromatography (GC) employing a nitrogen-phosphorus detector (NPD) and mass spectrometry (MS) was evaluated for the measurement of the 46 nitrogenand phosphorus-containing pesticides of U.S. EPA Method 507. Effects of pH, ionic strength, methanol content, and temperature on extraction were determined. Analytes were extracted into a bonded polydimethylsiloxane phase coated on a fused-silica fiber and then thermally desorbed in a GC injector and analyzed. Absorption-time and absorption-concentration profiles were obtained for each SPMEextractable pesticide. When analyzed by SPME GC/ NPD or by SPME GC/MS, 34 and 39 pesticides, respectively, were measured at levels lower than the EPA method detection limits and precision requirements. This method was applied to the analysis of contaminated well water, watershed, and streamwater and compared to U.S. EPA Method 507 findings. These results demonstrate that SPME is a valuable tool for the rapid screening of 39 EPA Method 507 nitrogen- and phosphorus-containing pesticides in water.
Introduction Most commonly used methods for the measurement of pesticides in drinking water involve liquid-liquid extraction, e.g., U.S. EPA Method 507 (1), and solid-phase extraction followed by GC or high-performance liquid chromatography (HPLC) (2-6). Although the liquid-liquid extraction method is very useful, it requires a large volume of highpurity solvent and a considerable amount of sample preparation time, making the method both labor intensive * Corresponding author e-mail address: bctomm@muccmail. missouri.edu.
S0013-936X(96)00040-5 CCC: $12.00
1996 American Chemical Society
and expensive. Although solid-phase extraction methods (2-6) use lesser amounts of solvents, these methods are still multiple-step procedures and are time consuming. Because of the increased emphasis on water analyses for pesticide contamination in both environmental and drinking water, ongoing research efforts in our laboratories seek alternate analytical techniques that are capable of screening large sample numbers without solvent extractions with a minimum number of analytical steps and that meet or exceed the detection limits of the EPA method. In 1990, an alternative extraction procedure employing solid-phase microextraction (SPME) of organic compounds from aqueous samples was introduced by Pawliszyn and co-workers (7, 8). In this new extraction method, a polydimethylsiloxane-coated fused-silica fiber is used and is immersed directly into a rapidly stirred aqueous solution with the analytes partitioning between water and the hydrophobic stationary phase on the fiber. The fiber with its holding assembly is then withdrawn, and the analytes are thermally desorbed in the GC injection port onto a capillary GC column for analysis (8). Pawliszyn and his co-workers applied this elegant method for the analysis of a variety of organic compounds, including alkyl substituted benzenes in water (9, 10); chlorinated hydrocarbons in water and air (11); and polynuclear aromatic hydrocarbons (7, 8), polychlorinated biphenyls (12), and phenols in water (13). In addition, the volatile organic compounds of U.S. EPA Method 624 have been analyzed using SPME followed by GC ion trap mass spectrometry (GC/MS) (14, 15). SPME has also been applied to the analysis of caffeine in beverages (16), for headspace analysis of halogenated volatiles in selected foods (17), and for liquid and headspace analysis of common flavor components (18). Application of SPME for the analysis of pesticides used on golf course greens (19), for the analysis of drugs (20), and in drinking water using polyacrylate fiber (21) has also been reported. This paper reports the application of SPME for 39 of the 46 nitrogen- and phosphorus-containing pesticides listed under the U.S. EPA Method 507 in water.
Experimental Section SPME fiber assemblies holding 1.0 cm long fused-silica fibers coated with a 100 µm thick layer of polydimethylsiloxane were purchased from Supelco, Inc (Bellefonte, PA). Methyl paraoxon, disulfoton sulfoxide, and disulfoton sulfone were purchased from Axact Standards (Commack, NY). All other nitrogen- and phosphorus-containing pesticides were purchased as mixtures dissolved in methyl tert-butyl ether or methanol from Crescent Chemical Co., Inc. (Hauppauge, NY). All organic solvents were purchased as their Optima-grade from Fisher Scientific (St. Louis, MO). Barnstead NANOpure deionized water of 18 MΩ quality was employed throughout this study for the making of solutions and for the rinsing and cleaning of glassware. Reacti-Vials, Teflon-coated septa, and triangular magnetic stirrers were purchased from Pierce Chemical Co. (Rockford, IL). From the purchased standard pesticide mixtures and single-component solutions were prepared 100-mL methanolic stock solutions. A 1.0-mL aliquot of these stock solutions was taken and diluted with deionized water to
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obtain 100-mL aqueous stock solutions, which were immediately used for the preparation of the desired concentration required for each respective SPME study. Aqueous stock solutions were prepared daily. In all cases, no significant absorption of the analytes (e0.2%) to the preparation glassware was observed when subjected to methanol rinsing and subsequent GC/NPD analysis. For sampling by SPME, a Teflon-coated triangular magnetic stirrer and 4.0 mL of an aqueous sample solution to be tested were placed in a 5.0-mL cone-shaped Glass Reacti-Vial and equipped with a Teflon-lined silicone septum cap. After the vial was positioned on a magnetic stirring plate (Fisher Thermix Stirring Plate, Model 210T), the fiber holder assembly containing the retracted SPME fiber was introduced through the Teflon-lined silicone septum of the open-top screw cap. The SPME fiber was then extended into the aqueous solution to a depth of 9 mm. The stirrer speed was carefully adjusted to 250 rpm so as to prevent any contact of the stirrer with the immersed delicate fiber. After each extraction, the fiber was then retracted into the holding assembly, removed from the vial, and immersed for 10 s in a vial containing 4.0 mL of deionized water in order to remove small amounts of adhering sodium chloride from the fiber before it was introduced for desorption into the injection port of the GC. Analysis of the rinsing solutions indicated that no loss of analytes due to rinsing of the fiber was demonstrable. Prior to each use, all new and used fibers were preconditioned by thermal desorption at 220 °C for 1 h and for 20 min, respectively, in the injection port of a Varian 3400 gas chromatograph. During this desorption process, the GC column oven temperature was maintained at 250 °C. If any carry over was observed by GC/NPD, the 20-min thermal preconditioning was repeated. Aqueous pesticide-containing solutions were extracted under varying NaCl concentrations, pHs, temperatures, and methanol concentrations to establish optimum extraction parameters. To determine the effect of the sodium chloride concentration on the extraction, pesticide solutions of 100 µg/L containing 0%, 5%, 10%, 20%, 25% (w/v), and saturated sodium chloride (certified grade, Fisher Scientific) were prepared, and 4-mL portions of these solutions were extracted for 20 min. The phosphate buffer employed for pH adjustment of the samples was prepared from an aqueous 100-mL solution of 0.1 M dipotassium hydrogen phosphate (certified ACS grade, Fisher Scientific). The phosphate solution was adjusted to pH 10.0 and to pH 8.0, 7.0, 5.0, and 2.0 with 0.1 N KOH and 0.1 N HCl, respectively. To determine the effect of temperature, SPME were performed at ambient temperature and at 4 °C. The effect of low methanol concentrations on extraction was studied on aqueous solutions containing 1%, 2%, 4%, 6%, and 10% methanol (v/v). An extraction time of 20 min was used for all experiments except for the absorption-time profiles, noted below. Precision (RSD %) of the SPME for 39 pesticides was determined by analyzing aqueous solutions containing 100 µg/L of the respective pesticide eight consecutive times. Extractions at ambient temperature of 4.0-mL aliquots of 100 µg/L of aqueous pesticide solutions saturated with sodium chloride and at pH 7.0 were performed for 20, 30, 60, 120, 180 and 240 min to produce absorption-time curves. Under these same conditions, absorptionconcentration curves were then generated by performing
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20 min SPME extractions of 0.01, 0.1, 0.5, 1, 2.5, 5.0, 7.5, 10, 30, 50, 75, and 100 µg/L pesticide solutions. Chromatographic separation was achieved on a Varian 3400CX gas chromatograph equipped with a 30 m 5% phenyl/95% dimethylsilicone fused-silica capillary column with a 0.32 mm i.d. and 0.25 µm film thickness (Quadrex Corporation, New Haven, CT). The GC unit had a septumequipped programmable injector (SPI) and a nitrogenphosphorus detector (NPD). The helium makeup gas, hydrogen, and air flow rates of the NPD detector were 30, 4.5, and 175 mL/min, respectively. The flow rate of the helium carrier gas was 4.0-mL/min. During the 5-min thermal desorption of the fiber, the injection port and oven temperatures were maintained at 220 and 100 °C, respectively. Immediately following the desorption period, the temperature programs for the injection port (50 °C/min to 250 °C) and the column oven (4 °C/min to 300 °C) were started at the same time. The detector temperature was kept at 300 °C. The GC detector response was standardized using the laboratory performance check solution (NPM507) for U.S. EPA Method 507 (Alltech Associates, Inc., Deerfield, IL). No correction to the data was made with regard to analytes not completely desorbed from the SPME fiber within the 5-min desorption step. For the GC/MS experiments, a Varian 3400CX GC/Saturn III ion trap mass spectrometer was utilized employing the same column and chromatographic conditions noted above for the GC/NPD experiments. Transfer line and manifold temperatures were maintained at 300 and 250 °C, respectively. Trifluorotributylamine (FC-43) was employed to tune the mass spectrometer. Segment breaks and segment tune factors were maintained at the default values. The mass range of 50-400 amu was scanned at 1 s per scan, and the detector filament and multiplier was programmed with an initial 4-min delay for each chromatographic run. Total ion count was utilized for each peak. Method detection limits were determined for both GC/NPD and GC/MS and were calculated based on 20-min extractions and at the accepted U.S. EPA Method 507 designated GC/NPD signal to noise ratio of 3:1. All glassware and magnetic stirrers were cleaned with detergent and water and by rinsing five times with acetone and then five times with methylene chloride (pesticide grade, Fisher Scientific). GC parameters, stirring speed of 250 rpm, and 4-mL extraction volume were held constant throughout the entire study.
Results and Discussion As described in U.S. EPA Method 507, the optimization of extracting into methylene chloride the 46 nitrogen- and phosphorus-containing pesticides, listed in Table 1, from groundwater and finished drinking water was achieved by increasing the ionic strength of the water to approximately 10% sodium chloride, adjusting the pH to 7.0 with a final concentration of 0.05 M potassium phosphate buffer, and performing multiple organic extractions. Since SPME has also been shown to be based upon an equilibrium between an analyte in solution and that in the bonded methyl silicone phase of the fiber coating (13), the influence of varying ionic strength, pH, methanol content, and temperature on the SPME extraction of U.S. EPA Method 507 pesticides and subsequent GC/NPD analysis were each tested at a concentration of 100 µg/L in 4.0-mL of water with an extraction time of 20 min. As shown in Figure 1,
TABLE 1
Gas Chromatographic Retention Times of EPA Method 507 Pesticides via SPME from Water retention timea
pesticide common nameb
retention time
pesticide common name
retention time
pesticide common name
4.68 8.15 9.23 10.52 10.65 10.90 11.59 13.66 13.90 16.49 16.93 17.42 19.61 19.71 19.82 20.26
dichlorvos (I) eptc (H) disulfoton sulfoxide (M) butylate (H) vernolate (H) mevinphos (I) pebulate (H) molinate (H) tebuthiuron (H) cycloate (H) ethoprop (N) chlorpropham (H) simazine (H) atraton (H) prometon (H) atrazine (H)
20.55 20.61 21.20 21.48 21.52 22.06 22.10 23.48 24.27 24.30 24.33 24.50 24.85 25.47 25.70 26.01
propazine (H) terbufos (I) pronamide (H) diazinon (I) disulfoton (I) terbacil (H) methyl paraoxon (M) disulfoton sulfone (M) ametryn (H) metribuzin (H) simetryn (H) alachlor (H) prometryn (H) terbutryn (H) bromacil (H) metolachlor (H)
26.82 27.07 27.48 29.95 30.00 30.02 30.35 30.63 30.94 31.0 34.00 35.30 40.37 45.97
triadimefon (F) MGK 264 (S) diphenamid (H) butachlor (H) carboxin (F) stirofos (I) fenamiphos (N) napropamide (H) merphos (H) tricyclazole (F) norflurazon (H) hexazinone (H) fenarimol (F) fluridone (H)
a Retention times given in minutes. Gas-liquid chromatographic (GC) separations were performed on 30 m, 0.32 mm i.d., fused-silica capillary column with a bonded 0.25 µm thick film of 5% phenyl/95% dimethylsilicone, in a GC unit with a septum-equipped programmable injector (SPI) and a nitrogen-phosphorus detector (NPD), as described in the Experimental Section. b EPA Method 507 pesticides followed by a parenthesized letter designating the respective compound to be the following: fungicide (F), herbicide (H), insecticide (I), nematicide (N), synergist for pyrethroids (S), or metabolite (M).
FIGURE 1. Effect of sodium chloride on SPME of EPTC, ethoprop, mevinphos, atrazine, propazine, prometryn, terbutryn, triadimefon and diphenamid. GC/NPD area counts are presented for 20-min SPME extractions in the presence of 0%, 10%, 20%, and saturated (sat.) sodium chloride (w/v) in water. Pesticide concentrations were each 100 µg/L, and extraction volumes were 4.0 mL.
which presents peak area vs extraction time of eight representative EPA 507 pesticides, significant increases in pesticide extractability were observed with increased sodium chloride concentrations. In contrast, all pesticides demonstrated decreases in SPME absorptivity when methanol was present in concentrations greater than 2%, with little or no effect of analyte recovery being demonstrated at lower concentrations. Although not shown, the effect of pH upon pesticide extractability with SPME was optimum for most pesticides around pH 7.0, whereas at pH 2.0, extractions of some pesticides were significantly impaired. Very little effect could be observed upon the extractibility of the pesticides when temperature varied from 4 °C to ambient temperature, regardless of ionic strength or pH. As a result of these data, all subsequent SPME extractions were performed at ambient temperature, at pH 7.0, with
a final 4.0-mL saturated sodium chloride solution. Since all stock solutions were prepared with methanol, it should be noted that the final methanol concentrations in aqueous solutions to be subjected to SPME were always less than 1%. Under these conditions, absorption-time profiles were generated for each EPA 507 pesticide that are compositely presented in Figure 2A-D. Each data point is the average of three independent extraction measurements. With the exception of hexazinone, terbacil, metribuzin, methyl paraoxon, tricyclazole, tebuthiuron, and bromacil, which demonstrated no affinity for the fiber coating, all pesticides exhibiting SPME fiber extractibility reach equilibrium within 4 h with most pesticides reaching greater than 90% of their final equilibrium value by 60 min. Each pesticide produced a unique absorption time curve that reflected the affinity of the pesticide for the SPME fiber coating and the response of the NPD to that pesticide. More rapid stirring or sonication of the solution, reported to enhance SPME binding in other studies (13), did not significantly alter these profiles. It is not a requirement for analysis that equilibrium be reached to utilize SPME as long as the extractions are carefully timed and the mixing conditions and extraction volumes remain constant (12, 13). Thus, a fixed extraction time of 20 min and the above-described optimal extraction conditions were employed in producing the absorption concentration curves in Figure 3 for each pesticide of EPA 507 that exhibited absorption by the SPME fiber. Each data point represents the average of three independent SPME analyses with standard deviations being comparable to those presented in Table 2 for each concentration tested. In all cases, a unique absorption concentration curve was observed for each pesticide via SPME GC/NPD analysis up to aqueous concentrations of 100 µg/L. From these data, the method detection limit for each pesticide was determined and is presented in Table 2. With the exceptions of disulfoton sulfoxide, mevinphos, disulfoton sulfone, simazine, carboxin, and fluridone, 34 pesticides could be quantified via SPME GC/NPD analysis at aqueous concentrations lower than that achieved by U.S. EPA Method 507 and below the maximum allowable concentrations permitted by the U.S. EPA (22). When analyzed by SPME
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FIGURE 2. SPME absorption-time profiles for EPA 507 pesticides (concentration ) 100 µg/L) in water. (A) (b) terbutryn, (0) prometryn, (2) EPTC, (3) ethoprop, ([) triadimefon, (") napropamide, (9) fenarimol, (O) propazine, (1) simetryn, (4) atraton; (B) (b) diazinon, (0) pebulate, (2) butylate, (3) terbufos, ([) vernolate, (") chlorpropham, (9) butachlor, (O) alachlor, (2) molinate, (4) stirofos, («) metolachlor, (]) MGK 264; (C) (O) disulfoton, (0) cycloate, (2) fenamiphos, (3) merphos, ([) ametryn, (") prometon, (9) atrazine, (O) disulfoton sulfone, (1) pronamide, (4) diphenamid; (D) (b) simazine, (0) norflurazon, (1) dichlorvos, (3) carboxin, ([) disulfoton sulfoxide, (") mevinphos.
FIGURE 3. SPME absorption-concentration profiles for EPA 507 pesticides in water. 20-min extractions were employed. (A) (b) terbutryn, (0) ethoprop, (2) EPTC, (3) prometryn, ([) propazine, (") triadimefon, (9) simetryn, (O) fenarimol, (1) atraton, (4) dichlorvos; (B) (b) disulfoton, (0) pebulate, (2) butylate, (3) diazinon, ([) terbufos, (") vernolate, (9) molinate, (O) cycloate, (1) napropamide, (4) metolachlor, («) butachlor, (]) MGK 264; (C) (b)fenamiphos, (0) merphos, (2) ametryn, (3) atrazine, ([) prometon, (") chlorpropham, (O) stirofos, (9) alachlor, (4) pronamide; (D) (b) diphenamid, (0) simazine.
GC/MS, only disulfoton sulfoxide and carboxin were not detectable below EPA 507 Method detection limits. All other SPME-extractable pesticides exhibited detection limits 2-10 times lower than the SPME GC/NPD limits when analyzed by SPME GC/MS. The precision of the SPME GC/NPD
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method was calculated for each compound (100 µg/L) following eight consecutive extractions. As shown in Table 2, the relative standard deviations (RSD %) ranged from (7% to (25%, which are below the (30% deviation permitted by the EPA 507 method.
TABLE 2
Method Detection Limits and Relative Standard Deviation (RSD %) of EPA 507 Pesticides Subjected to SPME GC/NPD and SPME GC/MS Analysis limit of detection (µg/L)
limit of detection (µg/L)
compoundsa
EPA 507 GLC/NPD
SPME GLC/NPD
SPME GLC/MS
RSDb (%)
dichlorvos eptc disulfoton sulfoxide butylate vernolate mevinphos pebulate molinate cycloate ethoprop chlorpropham simazine atraton prometon atrazine propazine terbufos pronamide diazinon disulfoton
2.50 0.25 0.38 0.15 0.13 5.00 0.13 0.15 0.25 0.19 0.50 0.075 0.60 0.30 0.13 0.13 0.50 0.76 0.25 0.30
1.50 0.02 37.50 0.05 0.10 22.50 0.04 0.11 0.13 0.03 0.22 0.36 0.40 0.16 0.11 0.04 0.08 0.65 0.06 0.04
0.08 0.01 8.13 0.02 0.02 4.32 0.01 0.02 0.03 0.01 0.04 0.01 0.04 0.02 0.03 0.01 0.01 0.02 0.01 0.01
15 12 11 25 15 8 20 10 11 11 18 19 8 12 7 12 13 12 15 9
compoundsa
EPA 507 GLC/NPD
SPME GLC/NPD
SPME GLC/MS
RSDb (%)
disulfoton sulfone ametryn simetryn alachlor prometryn terbutryn metolachlor triadimefon MGK 264 diphenamid butachlor carboxin stirofos fenamiphos napropamide merphos norflurazon fenarimol fluridone
3.80 2.00 0.25 0.38 0.19 0.25 0.75 0.65 0.50 0.60 0.38 0.60 0.76 1.00 0.25 0.25 0.50 0.38 3.80
8.25 0.40 0.18 0.30 0.02 0.01 0.22 0.12 0.38 0.26 0.25 9.50 0.25 0.15 0.13 0.13 0.18 0.22 27.25
1.10 0.03 0.02 0.01 0.01 0.01 0.02 0.01 0.03 0.03 0.01 3.50 0.02 0.05 0.03 0.02 0.03 0.02 2.50
14 16 9 8 17 18 19 16 15 7 21 11 17 12 17 19 8 19 16
a Compounds are listed in order of their gas chromatographic retention time. b RSD, relative standard deviation of eight individual SPME GC/NPD analyses, with each extraction of the respective pesticide at 100 µg/L being performed for 20 min. No significant change in precision was noted for intra- and interday analyses. Relative standard deviations for parallel samples analyzed by SPME GC/MS were similar to SPME GC/NPD results.
FIGURE 4. SPME GC/NPD analysis of drinking water spiked with 10 µg/L of each pesticide in EPA 507.
Possible carryover after thermal desorption of the polydimethylsiloxane-coated fiber in the GC injection system was investigated. For 33 pesticides, no carryover
from the previous run was observed at a concentration of 100 µg/L, indicating that these compounds are readily desorbed from the fiber during the 5.0-min injector
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FIGURE 5. SPME extraction of atrazine (1) from a contaminated well water sample and analyzed by GC/MS. Peaks due to SPME fiber bleed are noted (a).
desorption for GC/NPD analysis. However, for six pesticides, a carryover of analytes in the SPME fiber coating from the previous analytical run comparable to 1%, 2%, 5%, 8%, 14%, and 21% of the initial chromatographic peak areas was observed for disulfoton, diazinon, terbufos, fenamiphos, merphos, and fenarimol, respectively. These data indicate that some pesticides, such as merphos and fenarimol, require longer desorption times of approximately 10 min or higher desorption temperatures in order to achieve complete removal from the SPME fiber coating. To determine the loss of analytes through absorption onto the glass wall of the extraction vessel and possible carryover to the next experiment, a 4.0-mL water sample saturated with sodium chloride at pH 7.0 and containing 100 µg/L of each U.S. EPA Method 507 pesticide sample was added to a vial that was allowed to stir overnight. After analysis of the vial contents by SPME GC/NPD, which demonstrated recoveries >99% for each pesticide, the vial was then emptied, and both the vial and the magnetic stirring bar were gently rinsed 10 times with deionized water. The vial was then refilled with 4.0 mL of the above solution without pesticides and subjected to SPME extraction. Upon subsequent GC/NPD analysis, most pesticides were not detectable, and those that were observed resulted in the production of chromatographic peaks all less than 0.4% of the respective chromatographic area observed for a comparable SPME 100 µg/L of pesticide extraction. At concentrations lower than 50 µg/L or for extraction times that are shorter than 4 h, no extraction vessel carry over was observed for any EPA 507 listed pesticide. These absorption/desorption studies indicate that both absorption and desorption to the glass wall of the extraction vessel were not significant. Application of SPME GC/NPD to the analysis of drinking water is demonstrated in Figure 4, which shows a chromatogram of a drinking water sample spiked with 10 µg/L of each pesticide in U.S. EPA Method 507. As expected, those pesticides exhibiting high SPME absorptivity and high NPD sensitivity, noted above, are seen as producing pronounced chromatographic peaks. As a result of extensive preconditioning of the SPME fiber, very few peaks resulting from desorbed compounds from the fiber itself were noted. One persistent unknown peak was often observed eluting from the chromatographic column after merphos, seen in Figure 4.
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FIGURE 6. SPME GC/MS analysis of a contaminated watershed sample in an agricultural area: simazine (1), atrazine (2), ametryn (3), alachlor (4), and metolachlor (5).
FIGURE 7. SPME extraction of trifluralin (1), atrazine (2), alachlor (3), and terbutryn (4) from contaminated streamwater followed by GC/MS analysis. Peaks due to SPME fiber bleed are noted (a).
In addition to the influences of varying ionic strength, pH, alcohol content, and temperature on U.S. EPA Method 507 pesticides partitioning between the SPME fiber coating and the aqueous phase, extraction volume can also play an important factor. Employing the identical conditions utilized above for the 4.0-mL extractions, spiked 100-mL aqueous solutions of EPA 507 pesticides at concentrations of 100 µg/L were subjected to three independent 20-min SPME extractions and subsequent GC/NPD analysis. Compared to 4.0-mL extraction results, increases in sensitivity for most pesticides ranged from 50% to 110%. Propazine, prometryn, terbutryn, and triadimefon as examples demonstrated increases of 57%, 88%, 103%, and 79%, respectively. These results indicate that for some pesticides the detection limits can be significantly improved by increasing the sample volume. The effectiveness of the SPME technique as a screening tool for pesticide contamination in water was readily observed when tested on water samples that were collected from large farming districts. Figure 5 presents a representative GC/MS chromatogram of a contaminated well water sample acquired from a farm which was shown to contain 0.03 µg/L of atrazine. When analyzed by the EPA 507 method utilizing methylene chloride for the liquidliquid extraction and GC/NPD for quantitation, atrazine
could not be determined. Notably, Figure 5 also displays some peaks not observed by GC/NPD, which arise from the SPME fiber. Further conditioning of the fiber for an additional 30 min is recommended just prior to use for GC/MS analyses will diminish these peaks considerably, as seen in Figure 6. The GC/MS chromatogram in Figure 6 is of an SPME-extracted watershed sample obtained in the springtime during the corn planting season. The selective season-long weed control herbicides simazine, atrazine, and ametryn and the preemergence herbicides alachlor and metolachlor were shown to be present at concentrations of 0.02, 0.09, 0.09, 0.06, and 0.46 µg/L. When analyzed via the EPA 507 method, metolachlor was determined to be present at 0.47 µg/L, and we were not able to detect simazine, atrazine, ametryn, or alachlor at these concentrations. A streamwater sample collected mid-summer in a large farming district and analyzed by the SPME technique, shown in Figure 7, was found to contain atrazine (0.04 µg/ L), alachlor (0.03 µg/L), terbutryn (0.11 µg/L), and trifluralin (1.06 µg/L), a non-EPA 507 listed selective preemergence herbicide. When this sample was analyzed by EPA Method 507, terbutryn and trifluralin were found to be present at 0.13 and 1.07 µg/L, respectively. Atrazine and alachlor were not detectable.
Literature Cited (1) Methods for the Determination of Organic Compounds in Drinking Water; Report EPA/600/4-88/039; Environmental Monitoring Systems Laboratory, U.S. Environmental Protection Agency: Cincinnati, OH, 1988. (2) Schuette, S. A.; Smith, R. G.; Holden, L. R.; Graham, J. A. Anal. Chim. Acta 1990, 236, 141-144. (3) Di Corcia, A.; Marchetti, M. J. Chromatogr. 1991, 541, 365-373. (4) Di Corcia, A.; Marchetti, M. Anal. Chem. 1991, 63, 580-585.
(5) Di Corcia, A.; Marchetti, M. Environ. Sci. Technol. 1992, 26, 6674. (6) Balinova, A. J. Chromatogr. 1993, 643, 203-207. (7) Arthur, C. L.; Pawliszyn, J. Anal. Chem. 1990, 62, 2145-2148. (8) Zhang, Z.; Yang, M. J.; Pawliszyn, J. Anal. Chem. 1994, 66, 844A-853A. (9) Potter, D. W.; Pawliszyn, J. J. Chromatogr. 1992, 625, 247-255. (10) Arthur, C. L.; Killam, L. M.; Motlagh, S.; Lim, M.; Potter, D. W.; Pawliszyn, J. Environ. Sci. Technol. 1992, 26, 979-983. (11) Chai, M.; Arthur, C. L.; Pawliszyn, J.; Belardi, R. P.; Pratt, K. F. Analyst 1993, 118, 1501-1505. (12) Potter, D. W.; Pawliszyn, J. Environ. Sci. Technol. 1994, 28, 298305. (13) Buchholz, K. D.; Pawliszyn, J. Environ. Sci. Technol. 1993, 27, 2844-2848. (14) Arthur, C. L.; Pratt, K. F.; Motlagh, S.; Pawliszyn, J.; Belardi, R. P. J. High Resolut. Chromatogr. 1992, 15 (11), 741-744. (15) Arthur, C. L.; Potter, D. W.; Buchholz, K. D.; Motlagh S.; Pawliszyn, J. LC-GC 1992, 10 (9), 656-661. (16) Hawthorne, S. B.; Miller, D. J.; Pawliszyn, J.; Arthur, C. L. J. Chromatogr. 1992, 603, 185-191. (17) Page, B. D.; Lacroix, G. J. Chromatogr. 1993, 648 (1), 199-211. (18) Yang, X.; Peppard, T. J. Agric. Food Chem. 1994, 42 (9), 19251930. (19) Murata, K. Hokkaido Kankyo Kagaku Kenkyu Senta Shoho 1994, 21, 89-92. (20) Singer, K.; Wenz, B.; Seefeld, V.; Speer, U. Labor-Med. 1995, 18 (2), 112-118. (21) Eisert, R.; Levsen, K. Fresenius J. Anal. Chem. 1995, 351, 555562. (22) Drinking Water Regulations and Health Advisories; Office of Water, U.S. Environmental Protection Agency: Washington, DC, 1995.
Received for review January 17, 1996. Revised manuscript received July 1, 1996. Accepted July 1, 1996.X ES960040W X
Abstract published in Advance ACS Abstracts, October 1, 1996.
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