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ANALYST

FULLPAPER

THE

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Determination of organochlorine pesticides in river water by

gas chromatography-negative-ion chemical-ionization mass

spectrometry using large volume injection

Sadao Nakamura,* Takashi Yamagami and Shigeki Daishima

Yokogawa Analytical Systems Inc., 2-11-13 Nakacho, Musashino-shi, Tokyo 180-0006, Japan.

E-mail: sadao_nakamura@agilent.com

Received 22nd May 2001, Accepted 31st July 2001First published as an Advance Article on the web 21st September 2001

A method for the determination of 24 organochlorine pesticides by gas chromatography-mass spectrometry(GC-MS) with negative-ion chemical-ionization (NICI) using programmable temperature vaporizer (PTV)-basedlarge volume injection (LVI) is described. The ion source temperature was determined to be 150 C for theoptimized NICI-selected ion monitoring (SIM) conditions. PTV inlet parameters were also optimized. Thesensitivities of the pesticides by splitless-GC-NICI-MS were approximately 7.8360 times higher than those of thepesticides by splitless-GC-EI-MS. The sensitivities of the pesticides by LVI-GC-NICI-MS were over 80 timeshigher than those of the pesticides by spiltless-GC-NICI-MS. This method was applied to the determination of thepesticides in river water using micro liquidliquid extraction as sample preparation. The recoveries of thepesticides from a river water sample spiked with standards at 2 ng l21 and 20 ng l21were 75111% (RSD,2.915%) and 92105% (RSD, 0.55.6%), respectively. The methodical detection limits ranged from 0.004 to 2.2ng l21

Introduction

The human race has been synthesizing or isolating lots ofchemicals. Many of them are toxic to many organisms and theenvironment. Organochlorine compounds, such as polychlori-nated biphenyls (PCBs) and chlorinated pesticides, are also

toxic contaminants. It is important to monitor organochlorinecompounds at low levels in the environment. Therefore, weneed a sensitive method for determining organochlorinecompounds in the environment. To achieve lower detectionlimits, we generally need a method with high concentrationsample preparation such as gas chromatography-electron ion-ization mass spectrometry (GC-EI-MS) using liquidliquidextraction or solid-phase extraction with ~ 1000-fold concen-tration for aqueous samples.1,2 In GC, there are generally someapproaches to improve detection limits: concentrate samples;increase the sensitivity of the detector; increase the selectivityof the detector; and increase the injection volume. For thedetermination of organochlorine pesticides, negative-ion chem-ical-ionization mass spectrometry (NICI-MS) has a big ad-vantage for the sensitivity and selectivity of the detector.Electron capture NICI provides high sensitivity and selectivityfor electrophilic compounds. Therefore, GC-NICI-MS has beenapplied for the trace level determinations of electrophiliccompounds containing halogens, nitro groups, and highlyconjugated systems in environmental samples.35 On the otherhand, large volume injection (LVI) is another approach toimprove the detection limits. The typical injection volume forcapillary column analysis is 1 to 2 ml. With the LVI technique,good chromatography can usually be obtained with injectionvolumes of up to several hundreds of microliters. The majorityof the solvent is evaporated before transfer of the sample to theanalytical column. LVI is a good technique for the trace analysisof semivolatile compounds.68 Bagheri et al. reported thedetermination of PCBs in biological samples by GC-NICI-MSoff-line combined with liquid chromatography (LC) as theseparation.9 Their method provides high sensitivity and se-lectivity for PCBs with four or more chlorine atoms. Louter andcoworkers reported the determination of organochlorine pesti-

cides in water samples by on-line solid-phase extraction (SPE)-GC-EI-MS with direct injection of 80100 ml of sample extracton GC via retention gap techniques using an on-columninterface.1012 Their method allows the detection of the targetcompounds at levels below 0.1 mg l21 using a sample volume of10 ml. Hankemeier et al. developed a method for the

determination of triazines and organophosphorus pesticides byautomated on-line SPE-GC-flame-ionization detection (FID).13Their method allows the detection of the target compounds at0.20.7 mg l21 levels in river water using an on-columninterface with retention gap techniques for the injection of 50 mlof sample extract.

In this study, the combination of programmable temperaturevaporizer (PTV)-based LVI and NICI-MS was used for thedetermination of 24 organochlorine pesticides. Since thecombination provided much lower detection limits, a microliquidliquid extraction was used to simplify sample prepara-tion. This technique reduces the extraction time and the totalvolume of sample and solvent required for the analysis, andeliminates the step of concentrating the solvent. Very fewstudies on the determination of organochlorine pesticides havebeen performed by GC-NICI-MS using LVI. We developed aGC-NICI-MS method using LVI for the determination oforganochlorine pesticides. The method was optimized and thenapplied to the determination of organochlorine pesticides inriver water.

Experimental

Chemicals

The 24 organochlorine pesticides were obtained from Wako(Osaka, Japan). Acetone and hexane, both of reagent grade,were purchased from Merck (Darmstadt, Germany). Stockstandard solutions of the individual pesticides were prepared bydiluting each compound to a concentration of 1.0 mg ml21 inacetone. Sodium chloride (NaCl), reagent grade, was purchasedfrom Merck.

This journal is The Royal Society of Chemistry 2001

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Sample preparation (micro liquidliquid extraction)

River water was collected from the Singapore River. 0.3 g ofNaCl was added to the sample (10 ml), and then the vial wasshaken until the NaCl had completely dissolved. Two ml ofhexane was added to the sample, and then the vial was shakenfor 3 min. Then, 100 ml of the organic layer was analyzed byGC-NICI-MS with PTV.

Instrumentation

All GC-MS analyses were performed using an Agilent6890/5973 (Agilent Technologies, Palo Alto, CA, USA)equipped with PTV. The separation was carried out on a HP-5MS capillary column (30 m 3 0.25 mm id 3 0.25 mm filmthickness). Helium was used as the carrier gas with a columnflow rate of 1.2 ml min21 in the constant flow mode, andmethane served as the CI reagent gas with a flow rate of 2.5 mlmin21. The column temperature was held at 90 C for 5.32 min,then programmed at 20 C min21 to 170 C, then at 5 C min21to 250 C and finally at 15 C min21 to 280 C, which was heldfor 2.5 min. The PTV inlet was equipped with a deactivatedempty glass liner with multi baffles (1.5 mm id). Solvent ventmode was used for LVI, and twenty 5 ml injections were madefor a total of 100 ml by an autosampler equipped with a 10 mlsyringe. The PTV parameters of pause time between injections,initial temperature, final temperature, vent flow rate, sampletransfer time, and injection volume were optimized. The pausetime between injections was chosen as 0 s over the rangebetween 0 and 4 s: the responses for the target compoundsslightly decreased with increasing the time. The final tem-perature was chosen as 300 C over the range between 200 and400 C: although the responses for the target compoundsslightly increased with increasing the temperature, 300 C wasselected for decreasing the transfer of sample matrix to thecapillary column. The sample transfer time was selected as 1

min over the range between 0 and 2 min: the responses for thetarget compounds slightly increased with increasing the time

until 1 min. The injection volume was chosen as 100 ml forpractical repeatability; the responses for the target compoundswere linear between 50 and 350 ml. The optimization of theinitial temperature and vent flow rate is described in the Resultsand Discussion section. The vent flow rate was set at 50 mlmin21, and the vent pressure was set at 0 kPa until the injectionsequence was done (3.22 min). The normal inlet pressure wasrestored and the vent flow was turned off at 3.22 min. The ventflow remained off until it was set to 100 ml min21 at 5.32 min.

The inlet temperature was held at 20 C for 3.32 min, thenprogrammed at 280 C min21 to 300 C, which was held for 1min, then at 250 C min21 to 350 C, which was held for 2.8min, and finally at 20 C min21 to 250 C. The transfer linetemperature was kept at 280 C. The ion source temperature waschosen as 150 C after the optimization over the temperaturerange between 150 and 270 C. The mass spectrometer wasoperated in the NICI mode and with a scan range ofm/z 10 to570 at 1.36 scans s21. In the selected ion monitoring (SIM)mode, monitoring ions are listed in Table 1 and the ions weremonitored with a dwell time of 35 to 150 ms per single ion.

Results and discussion

Optimization of the PTV inlet parameters of initialtemperature and vent flow rate

PTV inlet parameters were optimized over the inlet initialtemperature range between 0 and 60 C and the vent flow raterange between 25 and 200 ml min21 (standard mixtureconcentration: 500 pg ml21 each; injection volume: 40 ml). Fig.1 shows the effect of the inlet temperature and the vent flow rateon peak areas fora-BHC, trans-nonachlor, and mirex. Most ofthe organochlorine pesticides showed similar results for thevarious combinations of the inlet temperature and the vent flowrate. At the inlet temperatures of 40, 50, and 60 C, most of the24 pesticides showed smaller peak areas over the whole range of

vent flow rates. The target compounds presumed to be vented invapor together with the solvent because peak areas tended to be

Table 1 Comparison of detection limits (DL, at S/N = 3) of EI-SIM using splitless, NICI-SIM using splitless, and NICI-SIM using LVI

EI-SIM NICI-SIM# Compounds

Monitor ions SplitlessaDL/pg ml21 Monitor ions Splitlessa DL/pg ml21 LVIb DL/pg ml21

1 a-BHC 181 1600 71 71 0.222 HCB 284 300 284 3.1 0.0173 b-BHC 181 1800 71 230 0.754 g-BHC 181 2300 71 130 0.215 d-BHC 181 3800 71 140 0.306 heptachlor 272 2200 35 30 0.227 aldrin 263 730 35 15 0.128 heptachlor epoxide 353 3300 388c 770c 1.3c

9 oxychlordane 387 7900 350 91 0.3710 trans-chlordane 373 2100 410 26 0.05911 o,p-DDE 246 310 35 83 0.3812 a-endosulfan 241 15000 406 42 0.07313 cis-chlordane 373 1900 410 46 0.1414 trans-nonachlor 409 2200 444 32 0.07215 dieldrin 79 17000 237d 300d 1.3d

16 p,pA-DDE 246 410 281e 1700e 5.6e

17 o,p-DDD 235 2400 35 520 3.018 endrin 263 21000 35 210 2.219 b-endosulfan 241 26000 406 81 0.05420 p,pA-DDD 235 260 35 600 3.221 endosulfan sulfate 272 5200 386 50 0.03022 p,pA-DDT 235 2400 35 520 0.6423 methoxychlor 227 550 35 1100 1.7

24 mirex 272 1600 368 12 0.15a Injection volume: 1 ml. b Injection volume: 100 ml. c m/z 35 could not be monitored because this compound overlapped oxychlordane under this condition.d m/z 35 could not be monitored because this compound overlappedp,p-DDE under this condition. e m/z 35 could not be monitored because this compoundoverlapped dieldrin under this condition.

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smaller with increasing inlet temperature and/or vent flow rate.At the inlet temperatures of 0 C, most of the pesticides showedmaximum peak areas under the vent flow rate of 100 ml min21.At 10 C, they showed maximum peak areas under 100 mlmin21. At 20 C, they showed maximum peak areas under 50 mlmin21. At 30 C, they showed maximum peak areas under 25 mlmin21. The repeatabilities of peak areas under the conditionsprovided maximum peak areas at each temperature (at 0 C with

a vent flow rate of 100 ml min21, at 10 C with a vent flow rateof 100 ml min21, at 20 C with a vent flow rate of 50 ml min21,and at 30 C with a vent flow rate of 25 ml min21) were 3.7, 3.1,3.2, and 5.5%, respectively, as average RSD value (n = 6) of allthe pesticides. Therefore, the parameters of 10 C with a ventflow rate of 100 ml min21 and 20 C with a vent flow rate of 50ml min21 showed better repeatabilities. For the sensitivity, theparameters of 20 C with a vent flow rate of 50 ml min21

Fig. 1 Effect of inlet initial temperature and vent flow rate on peak areas fora-BHC,trans-nonachlor, and mirex. 5: 0 C, -: 10 C, $: 20 C, 3: 30 C,+: 40 C, 1 50 C, 8 60 C.

Fig. 2 SIM chromatograms of organochlorine pesticides extracted from (upper) the river water spiked with the standards (20 pg) and (lower) the non-spikedriver water by LVI-GC-NICI-MS. 1: a-BHC, 2: HCB, 3: b-BHC, 4: g-BHC, 5: d-BHC, 6: heptachlor, 7: aldrin, 8: heptachlor epoxide, 9: oxychlordane, 10:trans-chlordane, 11: o,p-DDE, 12: a-endosulfan, 13: cis-chlordane, 14: trans-nonachlor, 15: dieldrin, 16: p,p-DDE, 17: o,p-DDD, 18: endrin, 19: b-endosulfan, 20:p,p-DDD, 21: endosulfan sulfate, 22p,pDDT, 23: methoxychlor, 24: mirex.

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provided better results than those of 10 C with a vent flow rateof 100 ml min21. The inlet initial temperature and vent flow ratewere chosen as 20 C and 50 ml min21, respectively.

Determination of organochlorine pesticides in SIM mode

A comparison of the detection limit levels (at a signal-to-noiseratio of 3) of the organochlorine pesticides by splitless-GC-EI-MS, splitless-GC-NICI-MS, and LVI-GC-NICI-MS is shown inTable 1. The sensitivities of the target compounds by splitless-GC-NICI-MS were 7.8360 times higher than those of thetarget compounds by splitless-GC-EI-MS except for heptachlorepoxide, o,p-DDE,p,p-DDE, o,p-DDD,p,p-DDD,p,p-DDT,and methoxychlor. For heptachlor epoxide, m/z 35 (the largestion) could not be monitored because this compound overlappedoxychlordane under this condition. For o,p-DDE, p,p-DDE,o,p-DDD, p,p-DDD, p,p-DDT, and methoxychlor, since thesensitivities by NICI-MS were 0.24.6 times higher than thoseby EI-MS, these pesticides did not provide high sensitivities forNICI-MS. For HCB, heptachlor, aldrin, oxychlordane, trans-chlordane, a-endosulfan, cis-chlordane, trans-nonachlor, diel-drin, endrin, b-endosulfan, endosulfan sulfate, and mirex, thesepesticides provided high sensitivities for NICI-MS because thesensitivity by NICI-MS were over 40 times higher than those byEI-MS.

The sensitivities of the target compounds by LVI-GC-NICI-MS were over 80 times higher than those of the targetcompounds by splitless-GC-NICI-MS. The detection limitsusing LVI-GC-NICI-MS ranged from 0.017 to 5.6 pg ml21. Thelinearity and repeatability of the NICI-MS method using LVIwere tested and the results are listed in Table 2. The calibrationcurves for all the pesticides were linear at 12 levels ofconcentration ranging from 0.2 to 1000 pg ml21 with correla-tion coefficients between 0.9943 and 0.9993. The repeat-abilities, expressed as a RSD (n = 6), for peak areas of all thepesticides were between 1.7 and 17% at 1 pg ml21 and between

2.4 and 14% at 10 pg ml21. The repeatabilities of the splitless-

GC-EI-SIM method and the splitless-GC-NICI-SIM methodwere also demonstrated and the results are listed in Table 2. Therepeatabilities for peak areas of all the pesticides were between0.9 and 12% at 50 000 pg ml21 by the splitless-GC-EI-SIMmethod, and between 1.5 and 11% at 500 pg ml21 and between2.2 and 8.2% at 5 000 pg ml21 by the splitless-GC-NICI-SIMmethod. NICI-MS showed almost the same performance as EI-MS at lower levels as judged by the comparison of RSD values.Although RSD values of o,p-DDD, endrin, p,p-DDD, andmethoxychlor showed over 10% due to worse signal-to-noiseratio, LVI-GC-NICI-MS showed almost the same performanceas splitless-GC-NICI-MS. For o,p-DDD, endrin, p,p-DDD,and methoxychlor, good repeatabilities were obtained at 100 pgml21 with RSD values between 3.3 and 7.9%.

Application to river water

Interference of river water matrix. Standards (2 and 20 pg:0.2 and 2 ng l21 as concentration in river water) were added to10 ml of a river water sample, and then the river water wastreated by the micro liquidliquid extraction method describedin the Experimental section. The extract spiked with the

standards and the non-spiked extract were analyzed by GC-NICI-MS using LVI. a-BHC, -BHC, g-BHC, endosulfansulfate, and p,p-DDT were also detected in the non-spikedsample (a-BHC: 0.30, b-BHC: 0.38, g-BHC: 0.75, endosulfansulfate: 0.59, and p,p-DDT: 0.61 ng l21). All the pesticidescould be determined without interference from the river matrix.Fig. 2 shows NICI-SIM chromatograms of the pesticidesextracted from the river water spiked with the standards (20 pg)and from the non-spiked river water. The detection limitsevaluated in the river water are listed in Table 3, and rangedfrom 0.004 to 2.2 ng l21.

Recovery. The standards were added to 10 ml of a river watersample (20 and 200 pg as the spiked amounts; 2 and 20 ng l21

as the concentration in the river water), and then the spiked

Table 2 Repeatabilities (n = 6) and correlation coefficients of calibration curves

NICI-SIMsplitlessa LVIb

# Compounds

EI-SIM splitlessa

RSD (%) 50 000pg ml21

RSD (%) 500 pgml21 5 000 pg ml21

RSD (%) 1 pgml21 10 pg ml21

Correlationc

coefficient

1 a-BHC 1.7 1.5 2.6 8.9 4.3 0.99772 HCB 1.6 1.8 2.2 6.8 2.4 0.99433 b-BHC 3.5 8.6 3.4 9.9 2.7 0.99824 g-BHC 2.3 5.2 2.9 15 4.7 0.99765 d-BHC 2.2 5.5 2.9 11 2.5 0.99706 heptachlor 1.5 3.0 4.1 17 7.7 0.99857 aldrin 0.9 1.6 2.3 6.9 3.7 0.99508 heptachlor epoxide 2.1 nd 7.3 nd 3.4 0.99859 oxychlordane 12 2.3 2.6 1.7 2.5 0.9990

10 trans-chlordane 2.9 3.5 2.5 8.1 2.4 0.998311 o,p-DDE 2.1 2.6 2.5 6.2 2.4 0.997712 a-endosulfan 3.8 1.9 2.5 9.0 3.7 0.998713 cis-chlordane 2.4 2.9 2.7 5.6 2.7 0.998814 trans-nonachlor 3.1 2.8 2.3 3.7 2.6 0.998915 dieldrin 2.0 9.5 3.8 nd 7.9 0.994816 p,pA-DDE 2.2 nd 8.2 nd 9.7 0.996517 o,p-DDD 2.4 nd 4.7 nd 14 0.997118 endrin 6.1 11 4.1 nd 13 0.997819 b-endosulfan 7.1 7.0 3.2 7.3 6.4 0.998320 p,pA-DDD 3.0 nd 5.0 nd 13 0.997621 endosulfan sulfate 2.7 3.7 3.7 9.9 4.2 0.9989

22 p,pA-DDT 2.2 nd 4.2 14 5.8 0.998523 methoxychlor 2.4 nd 3.9 nd 11 0.997124 mirex 3.5 1.6 2.6 8.6 3.5 0.9993

a Injection volume: 1 ml. b Injection volume: 100 ml. c Concentration range: 0.21000 pg ml21 nd: not detected.

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sample was treated by the micro liquidliquid extractionmethod. Subsequently, the extract was analyzed by GC-NICI-MS using LVI. The recovery and reproducibility were testedand the results are listed in Table 3. Good recoveries wereobtained for all the pesticides with values between 75 and 111%at 2 ng l21 and between 92 and 105% at 20 ng l21. Practical

reproducibility was obtained for all the pesticides with RSDvalues (n = 6) between 2.9 and 15% at 2 ng l21 and between 0.5and 5.6% at 20 ng l21 for the peak areas.

Conclusions

A rapid, sensitive, and selective GC-NICI-MS method for thedetermination of 24 organochlorine pesticides in river waterwas developed. Significant advantages of the method are thatNICI-MS provided high sensitivity for the pesticides; PTV-based LVI improved the sensitivities by the 100 ml injectionvolume. Therefore, the combination of NICI-MS and LVIallows the detection of levels in the range 0.0042.2 ng l21 levelof the pesticides in river water using micro liquidliquidextraction (5-fold concentration). The method also provides awide range of linearity, satisfactory recovery, and goodreproducibility.

References

1 H. M. Kuch and K. Ballschmiter,Fresenius J. Anal. Chem., 2000,366, 392.

2 T. Ibaraki, C. Oguma, A. Tanabe, K. Kawata, M. Sakai and I. Kifune,Bunseki Kagaku, 1999, 48, 637.

3 M. Yasin, P. J. Baugh, P. Hancock, G. A. Bonwick, D. H. Davies andR. Armitage,Rapid Commun. Mass Spectrom., 1995, 9, 1411.

4 G. A. Bonwick, C. Sun, P. Abdul-Latif, P. J. Baugh, C. J. Smith, R.Armitage and D. H. Davies,J. Chromatogr. A , 1995, 707, 293.5 P. Haglund, T. Alsberg, . Bergman and B. Jansson, Chemosphere,

1987, 16, 2441.6 H.-J. Stan and M. Linkerhgner,J. Chromatogr. A , 1996, 727, 275.7 J. C. Bosboom, H.-G. Janssen, H.-G. J. Mol and C. A. Cramers,J.

Chromatogr. A, 1996, 724, 384.8 H. G. J. Mol, M. Althuizen, H.-G. Janssen and C. A. Cramers,J. High

Resolut. Chromatogr., 1996, 19, 69.9 H. Bagheri, P. E. G. Leonards, R. T. Ghijsen and U. A. Th. Brinkman,

Int. J. Environ. Anal. Chem., 1993, 50, 257.10 A. J. H. Louter, C. A. van Beekvelt, P. Cid Montanes, J. Slobodnik,

J. J. Vreuls and U. A. Th. Brinkman, J. Chromatogr. A, 1996, 725,67.

11 J. Slobodnik, A. C. Hogenboom, A. J. H. Louter and U. A. Th.Brinkman,J. Chromatogr. A , 1996, 730, 353.

12 J. Slobodnik, A. J. H. Louter, J. J. Vreuls, I. Liska and U. A. Th.

Brinkman,J. Chromatogr. A , 1997, 768, 239.13 Th. Hankemeier, P. C. Steketee, J. J. Vreuls and U. A. Th. Brinkman,

J. Chromatogr. A , 1996, 750, 161.

Table 3 Recoveries of organochlorine pesticides from river water andreproducibilities (n = 6), and methodical detection limits

# Compounds

Recovery, %(RSD, %)spiked 20 pg in10 ml riverwater

Recovery, %(RSD, %)spiked 200 pgin 10 ml riverwater

Methodicaldetectionlimits/ng l21

1 a-BHC 85 (4.7) 102 (3.9) 0.091

2 HCB 75 (3.4) 93 (2.1) 0.00403 b-BHC 89 (5.5) 104 (2.4) 0.154 g-BHC 86 (6.1) 103 (2.9) 0.0425 d-BHC 89 (4.9) 102 (2.7) 0.0786 heptachlor 107 (8.6) 97 (5.6) 0.207 aldrin 82 (4.9) 92 (1.6) 0.108 heptachlor epoxide 111 (15) 97 (3.0) 1.59 oxychlordane 88 (3.2) 101 (1.7) 0.23

10 trans-chlordane 83 (3.3) 98 (0.8) 0.01211 o,p-DDE 93 (5.1) 100 (2.6) 0.1012 a-endosulfane 92 (3.9) 100 (1.4) 0.03413 cis-chlordane 85 (3.1) 97 (0.5) 0.02814 trans-nonachlor 85 (2.9) 95 (3.9) 0.01415 dieldrin 106 (15) 95 (1.9) 0.3816 p,pA-DDE 104 (12) 95 (2.3) 2.217 o,p-DDD 93 (6.9) 103 (2.8) 0.6018 endrin 105 (5.9) 113 (1.5) 0.45

19 b-endosulfan 94 (3.7) 99 (1.2) 0.05820 p,pA-DDD 97 (11) 100 (2.3) 0.6321 endosulfan sulfate 95 (4.9) 102 (1.5) 0.006022 p,pA-DDT 98 (4.3) 103 (1.4) 0.1323 methoxychlor 11 (8.8) 105 (2.0) 0.7724 mirex 89 (3.8) 97 (2.0) 0.081

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