Environ. Sci. Technol. 1993,27,2352-2359
Comparison of On-Line Solid-Phase Disk Extraction to Liquid-Liquid Extraction for Monitoring Selected Pesticides in Environmental Waters Serge Chiron,? Amadeo Fernandez Alba,* and DamiA Barcel6'gt Environmental Chemistry Department, CID-CSIC, c/Jordi Girona, 18-26, 08034 Barcelona, Spain, and Faculty of Sciences, Almeria Campus, University of Granada, 0407 1 Almeria, Spain
A multiresidue method for the analysis of 30 pesticides and various transformation products (TPs) has been developed. On-line solid-phase extraction (SPE) using 10 Empore 4.6-mm extraction disks containing C-18 and/ or styrene-divinylbenzene were placed in a disk holder and were used coupled on-line with liquid chromatography (LC) with either UV or postcolumn fluorescence derivatization (EPA method 531.1). The on-line SPE method, using 150 and 10 mL of water for LC-UV and postcolumn fluorescence derivatization, respectively, has been compared with the liquid-liquid extraction (LLE) method involving dichloromethane (NPS method 4) and 1 L of water. At a spiking level of 0.3 pg/L in the Ebro (Spain) and Rhbne (France) river waters and Almeria (Spain) well waters, recoveries varied between 70 and 100% , except for the polar TPs that were either extracted with poor recoveries or interferences were noticed in early-eluting peaks of the LC-UV traces. Confirmation was achieved by using selected-ion monitoring mode in thermospray LC-MS in the positive and negative ion modes. The method permitted the determination of atrazine, simazine, alachlor, and molinate (Ebroriver waters) and methiocarb sulfone, methiocarb, methomyl, butocarboxim, and carbaryl (Almerfa well waters) at the 0.01-0.5 pg/L level.
Introduction Liquid chromatography (LC) systems used for environmental pesticide analyses were extensively reviewed in a recent paper (I). Different EPA and National Pesticide Survey (NPS) methods include the analysis of carbamates, e.g., aldicarb and their polar transformation products (TPs), e.g., carbofuran phenol (2, 3). As regards the isolation of pesticides from water samples, liquid-liquid extraction (LLE) methods using dichloromethane have been reported (4)in the literature covering several groups of pesticides and have also been recommended by the US. EPA through their NPS (2,3). As an alternative to LLE, solid-phase extraction (SPE) procedures have been implemented in the last few years. SPE methods can be easily converted into fully automated online systems coupled to LC (5-11). Coupling of various precolumns of different chemical composition, whether isolated or serially connected, packed usually with C-18 and styrene-divinylbenzene copolymer (PRP-1) have been demonstrated to exhibit a better performance than other types of precolumns for relatively polar compounds (5,6). Recently, the on-line coupling of C18-bonded silica Empore extraction disks with LC-UV (12) and LCpostcolumn fluorescenceand UV-visible spectroscopy (13) has allowed the determination of various groups of
* Author to whom correspondence should be addressed.
+ CID-CSIC.
University of Granada. 2952
Envlron. Sci. Technol., Vol. 27, No. 12. 1993
pesticides, (e.g., triazines, carbamates, and their polar TPs), with better breakthrough volumes than PLRP-S, which indicates the high trapping possibilities of the 4.6-mm Empore disks and a particle size of 8 pm. However, until now, no application has been reported with on-line SPE using polystyrene-divinylbenzeneEmpore extraction disks in water analysis. The combination of LC with MS is the most powerful system for confirmation of pesticides in water matrices and avoids false positives. Of the different LC-MS systems, the thermospray (TSP) and particle beam (PB) interfaces are probably the most widely used in water analysis. References on the use of both TSP (14,15) and PB (16) for the analysis of a variety of pesticides included in the NPS at a microgram per liter range in water are reported. In view of the different approaches to determine pesticides in water, it is the aim of the present work (i) to compare on-line SPE techniques using two types of membrane extraction disks, (2-18 and polyestyrenedivinylbenzene (SDB) with conventional and well-established dichloromethane LLE; (ii) to apply the developed procedure to polar pesticides and TPs included in EPA method 531.1, e.g., aldicarb, aldicarb sulfoxide, and NPS method 4 (propanil, carbofuran phenol, deethylatrazine); (iii) to establish a good cleanup method for the different types of waters analyzed (from Ebro and Rhbne rivers and well waters); and (iv) to use two different types of detection, UV and postcolumn fluorescence according to EPA method 531.1for N-methyl and 0-(methyl carbomyl) oxime carbamates. In addition, thermospray mass spectrometry will serve as the confirmation technique to avoid false positives present in the water matrix. The different approaches used show application for the determination of 30 pesticides of different chemical nature and their corresponding TPs, which are of interest within the EEC Drinking Water Directive (17)and the NPS-US. EPA monitoring program (2, 3).
Experimental Section Chemicals. HPLC-grade water, acetonitrile, gradientgrade Lichrosolv, and methanol from Merck (Darmstadt, Germany) were passed through a 0.45-pm filter before use. Trifluoroacetic acid was purchased from Aldrich (Steinheim, Germany). Aldicarb sulfoxide, aldicarb sulfone, oxamyl, methomyl, deisopropylatrazine, 3-hydroxy-7phenolcarbofuran, deethylatrazine, 3-hydroxycarbofuran, methiocarb sulfoxide, methiocarb sulfone, methiocarb, 3-ketocarfuranphenol, 3-ketocarbofuran, 1-naphthol, carbofuran, butocarboxim, aldicarb, 8-hydroxybentazone, bentazone, symazine, baygon, carbaryl, chlortoluron, MCPA, atrazine, isoproturon, propanil, molinate, alachlor, and metolachlor were purchased from Promochem (Wesel Germany). UV-Visible Detection. The eluent was delivered by a Model 250 binary high-pressure pump from Perkin Elmer 0013-936X/93/0927-2352$04.00/0
0 1993 Amerlcan Chemical Society
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Flgure 1. LC chromatograms of the pesticide mixture containing 10 mglL (injection 20 pL) each of the following: (1) aldlcarb sulfoxide, (2) aldlcarb sulfone, (3) oxamyl, (4) methomyl, (5) 3-hydroxy-7-phenolcarbofuran, (6) delsopropylatrazine, (7) 3-hydroxycarbofuran, (8) methiocarb sulfoxide, (g)deethylatrazine,(10) methiocarbsulfone, (1 1) 3-ketocarfuranphenol, (12) butoxycarboxim,(13) aldicarb, (14) 3-ketocarbofuran, (15) 8-hydroxybentazone, (16) simazine, (17) baygon, (18) carbofuran, (19) bentazone, (20) carbaryl, (21) chlorotoluron, (22 30) MCPA -4- 1-naphthol, (23) atrazine,(24) isoproturon,(25) propanil, (26) methiocarb, (27) molinate, and (28-29) alachlor -t metolachlor. LichroCartcartridge column (25 cm X 4.6 mm i.d.) packed with 4-pm Supersphere 60 RP-8 from Merck. Gradient elution program: from 5 % A and 95% B to 20% A-80% B in 15 mln; from 20% A-80% B to 30% A-70% Bin 20 min; from 30% A-70% B to 55% A-45% B in 20 min; lsocratic for 10 min; from 55% A-45% B to 100% A in 10 min; isocratic for 10 min; back to initial conditions postrun 10 min; flow rate 0.8 mL/mln. (A) LC-UV detection at 220 nm and (6) postcolumn fluorescence detection.
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(Norwalk, CT) coupled to a LC-95 UV/vis spectrometric detector from Perkin Elmer. Samples were injected via a Rheodyne 2 0 - ~ Lloop (Cotati, CAI. A LiChrocart cartridge column (25 cm X 4.6 mm i.d.) packed with 4-pm Supersphere 60 RP-8 from Merck (Darmstadt, Germany) was used. Gradient elution was performed from an eluent containing 5 % A [acetonitrile-methanol-water (404020)l and 95% B [acetonitrile-water (10:90)1to 20% A-80% B in 15 min, from 20% A-80% B to 30% A-70% B in 20 min; from 30% A-70% B to 55% A-45% B in 20 min; isocratic mode for 10 min; from 55% A-45% B to 100% of A in 10 min; isocratic mode for 10 min and back to the initial conditions in 5 min, postrun time 5 min at a flow rate of 0.8 mL/min. Figure 1A shows a typical LC-UV separation at 220 nm of the pesticide standard mixture. Postcolumn Fluorescence Derivatization. The LC eluent was delivered by a Model 250 binary LC pump from Perkin Elmer coupled to a PCX 5000 carbamate postcolumn analysis module from Pickering Laboratories (Mountain View, CA). Postcolumn reaction was carried out as described earlier (13). A Model LC 240 fluorescence detector from Perkin Elmer (Beaconsfield, UK) was
used at excitation and emission wavelengths of 330 and 465 nm, respectively. A P E Nelson Model 1020 data system was used for data collection. Samples (20pL) were injected via a Rheodyne Model 7125 syringe loading sampler. The LC conditions used were as follows: gradient elution program from 5% A and 95% B to 20% A-80% B in 20 min; from 20% A-80% B to 30% A-70% B in 20 min; from 30% A-70% B to 65% A-35% B in 20 min; from 65% A-35% B to 100% A in 7 min; back to initial conditions 5 min; flow rate 0.8 mL/min. Figure 1B shows a typical LC-postcolumn fluorescence derivatization chromatogram of a standard pesticide mixture. On-Line SPE Technique. The on-line system used has been described in our previous work (23). The membrane disks were placed in the disk holder, which was placed in a Must column switching device from Spark Holland (AS Emmen, The Netherlands) and connected to an SSI Model 300 LC pump from Scientific System Inc. (State College, PA), which delivered the water sample containing the pesticides. The disks were first conditioned by flushing 10 mL of methanol and then 10 mL of HPLC water (pH 3, trifluoroacetic acid) at a flow rate of 1mL/ min. Latter 150 mL of water, either river or well water, was preconcentrated at a flow rate of 2 mL/min. To improve the cleanup step, samples were previously acidified at pH 3 with sulfuric acid. A stable and reproducible desorption step was obtained by using a flow rate of 1.1mL/min for 3 min, the pressure of the system being 4500 psi. Afterward, the flow rate was reduced to 0.8 mL/min, the common flow used. for analytical determinations, and the pressure went down to 2500 psi. This on-line preconcentration system was coupled to the UV-visible and postcolumn fluorescencederivatization systems described above. Water volumes of 150 and 10 mL were used, respectively,for UV-visible and postcolumn fluorescence detection. QuantitativeAnalyses. Quantification by LC-UVwas performed using UV absorption at 220 or 215 nm and/or using the aforementioned postcolumn reaction method with fluorescence detection at excitation and emission wavelengths of 330 and 465 nm, respectively. External standard calibration graphs were constructed and were linear over a concentration range of 0.01-5 (for LLE) and 0.05-0.7 pg/L (for on-line C-18 Empore disks). The calibration graphs were constructed only for compounds that showed recoveries higher than 70% using both methods (see Table I). Sample Preparation. Estuarine water samples from Ebro Delta (Tarragona, Spain) and RhBne Delta (Arles, France) and groundwater samples (Almeria, Spain) of 10150 mL were filtered over a 0.45-pm membrane filter (Millipore, Bedford, MA) and then were spiked with the different pesticides, giving final concentrations of 0.2-0.3 pg/L. For the SPE experiments, the pH of the sample was kept at 3 using sulfuric acid. For the postcolumn derivatizatioq analyses, the sample pH was maintained at pH 6.5 since at lower pH 1-naphthol was partially protonated and was not trapped on the (2-18 bonded silica disk. LLE was carried out using 1 L of the different water types spiked with the pesticides at 2.5pg/L. After agitation the solutions were extracted with 50 mL of dichloromethane, following the National Pesticide Survey method 4, described elsewhere (2, 3). For a complete Environ. Sci. Technol., Vol. 27,
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Table I. Average Percent Recovery (av) and Coefficient of Variation (CV) (n = 5 for Each Pesticide) of Pesticides Spiked in Rhi3ne River Water Using On-Line S P E with Empore Disks. A
peak no. 1 2
compounds
av
aldicarb sulfoxide aldicarb sulfone oxamyl methomyl 3-hydroxy-7-phenolcarbofuran deisopropylatrazine 3-hydroxycarbofuran methiocarb sulfoxide deethylatrazine methiocarb sulfone 3-ketocarbofuran phenol butocarboxim aldicarb 3-ketocarbofuran 8-hydroxybentazone simazine baygon (propoxur) carbofuran bentazone carbaryl chlortoluronb MCPA 1-naphthol atrazine isoproturon propanil methiocarb molinate metolachlor-alachlorc
nd nd nd nd nd 17 50 nd 55 nd 65 91 78 74 20 87
B
cv
av nd nd nd nd nd
C
cv
av
D
cv
av
E CV
cv
av
87 6 18 24 90 4 36 18 3 12 85 4 70 7 4 12 2 88 4 83 5 nr 94 11 6 10 22 14 22 10 nr 17 36 7 7 54 8 nd 75 3 5 83 8 nd nd 11 6 24 78 9 48 5 44 8 nr 8 60 7 10 nd nd 6 47 73 11 11 5 11 nd 61 nr 6 89 12 10 85 4 29 8 93 7 3 65 13 74 8 8 33 7 94 10 3 62 14 8 8 12 68 10 72 6 8 68 15 nd 10 42 nd nr 11 16 84 3 3 10 22 nr 8 97 17 72 5 22 78 8 10 3 91 93 3 18 9 72 7 75 21 4 10 95 3 90 70 19 65 6 11 30 7 nr 7 81 20 80 3 a2 12 2 23 10 80 5 109 21 93 5 90 5 nr 100 8 7 35 20 25 30 12 15 40 7 nr 34 20 22 nd nd nd 72 5 nd 23 92 23 a 5 10 4 85 nr 99 24 94 4 87 6 nr 10 8 23 100 78 25 72 5 8 10 12 3 94 nr 85 26 78 5 7 21 10 4 90 5 96 92 8 nr 10 70 27 88 20 17 5 95 7 6 90 51 28-29 92 7 nr 10 0 (A) nd, not detected, due to matrix interferences or high breakthrough volumes; nr, not responding to the detection 10 C-18, (B) 6 C-18 and 4 SDB, (C) 10 SDB disks. Water volume preconcentrated, 150 mL at 2 mL/min; spiking level, 0.3 pg/L; UV detection, 220 nm. (D)10 (2-18 disks; water volume preconcentrated, 10 mL at 2 mL/min; spiking level, 0.2 pg/L; postcolumn fluorescence. (E) using CH2C12 LLE (n = 6); spiking level, 2.5 pg/L; water volume, 1L. First, 1 g of NaCl is added to the water and the sample is extracted with CH2C12. Afterwards, the water sample is acidified with HzS04 at pH
