Mass spectrometric analysis of nitrogen- and phosphorus-containing pesticides by liquid chromatography-Mass Spectrometry

A series of nitrogen- and phosphorus-containing pesticides (amines, anilides, carbamates, phosphonates, phenylureas, sulfonylureas, and triazines) was examined by thermospray (TSP) ionization. A method is described that employs off-line and on-line solid-phase extraction and TSP liquid chromatography-mass spectrometry (LC-MS) with time-scheduled selected ion monitoring (SIM) for environmental monitoring of these pesticides in aqueous samples. SIM detection limits for the pesticides analyzed in conjunction with reversed-phase high-performance liquid chromatography range from 40 to 600 pg. In addition, methods for inducing fragmentation in thermospray LC-MS are presented. The structural information gained therefrom can be used to confirm a tentative identification. Therefore, fragmentation pathways under certain experimental conditions were investigated. Atmospheric pressure chemical ionization, electrospray, fast-atom bombardment, ²⁵²Cf plasma desorption, and collision-activated dissociation spectra are presented for several pesticides to confirm the proposed pathways and to gain additional and complementary information. Further confirmation may be achieved by postcolumn addition of different alkylated amines to the carrier stream in the TSP operation to induce postcolumn on-line derivatization (POD) reactions in the condensed phase of the vaporizer probe with selected pesticides. Additional clustering reactions in combination with solvent-mediated chemical ionization are observed by the POD technique. Both processes can be used to enhance the structural information from TSP spectra and thus the specificity of the method.     

A new quantitative thermospray LC-MS method for nicotine and its metabolites in biological fluids

A rapid thermospray liquid chromatography-mass spectrometry (TSP LC-MS) method is described for the simultaneous determination of nicotine and 17 of its metabolites. Chemical ionization of nicotine and its metabolites separated by reversed-phase HPLC is achieved by postcolumn addition of ammonium acetate buffer with the filament of the ion source turned off. Quantification is accomplished by selectively monitoring the unique protonated molecular ion of each metabolite. Trideuterated cotinine serves as an internal standard. Linear responses for cotinine, demethylcotinine, and trans-3'-hydroxycotinine were observed over a concentration range of 20-8000 ng/mL, and 80-8000 ng/ml for nicotine and nicotine-1'-N-oxide. Of the 17 metabolites examined, only nicotine, cotinine, demethylcotinine, and trans-3'-hydroxycotinine were detected in smokers' urine.     

A new multi-residue method for analysis of pesticide residues in fruit and vegetables using liquid chromatography with tandem mass spectrometric detection

A new multi-residue method for determination of pesticide residues in a wide variety of fruit and vegetables, using the National Food Administration (NFA) ethyl acetate extraction and determination by means of LC-MS/MS, is presented. The method includes pesticides normally detected by LC-UV or LC-fluorescence such as benzimidazoles, carbamates, N-methylcarbamates and organophosphorus compounds with an oxidisable sulphide group as well. After extraction with ethyl acetate, the extract is concentrated and an aliquot of the extract is evaporated to dryness and redissolved in methanol before injection on LC-MS/MS. The method has been validated for 57 different pesticides and metabolites. Representative species from different commodity groups were chosen as matrices in order to study the influence from different matrices on recoveries. The fortification levels studied were 0.01-0.5 mg kg(-1). Matrix effects were tested for all matrices by means of standard addition to blank extracts. The matrix effect, expressed as signal in solvent compared to signal in matrix, was in general found to be small. The obtained recoveries are, with a few exceptions, in the range 70-100%. The proposed method is quick and straightforward and no additional clean-up steps are needed. The method can be used for the analysis of all 57 pesticides in one single determination step at 0.01 mg kg(-1).     

Thermospray high-performance liquid chromatographic-mass spectrometric characterization of biological macromolecules. I. Analysis of acid hydrolysate of peptides

A method for the routine analysis of phenylthiocarbamyl (PTC) amino acids by thermospray high-performance liquid chromatography-mass spectrometry (TSP LC-MS) is described. Data were acquired on a small dedicated TSP LC-MS system in which the temperature of the vaporizer and ion source block were optimized. PTC-amino acids exhibited unique TSP mass spectra containing sufficient fragment ions to determine structural data. Therefore, using this method the amino acids contained in the acid hydrolysates of unique and modified peptides were able to be positively identified. Additionally, the amino acid composition of peptides as determined by TSP LC-MS in the selected ion monitoring mode corresponded well with the theoretical value. The detection limits for the PTC-amino acids were at the low picomole level.     

Pesticide residues analysis in honey using ethyl acetate extraction method: validation and pilot survey in real samples

This paper presents a cost-effective and validated multi residue confirmatory method for the determination of 167 chemically different pesticides and a survey study on Cyprus honey samples. This method uses ethyl acetate for the extraction of pesticides from honey and the determination is performed with liquid chromatography (LC) coupled to mass spectrometry (MS) operating in tandem mode (MS/MS) and with GC–ECD (gas chromatography with electron capture detector) analysis. The LC-MS/MS analytical system is especially important in the analysis of polar and non-volatile pesticides. For the validation of the method, blank honey samples were spiked with 146 pesticides (organophosphorous, carbamates, triazoles, amides, neonicodinoids, strobilurines, phenylureas, bendimidazoles and others) for the LC-MS/MS analysis at three levels: 0.01, 0.05 and 0.1 mg kg^?1 and with 21 pesticides for the GC-ECD analysis at two levels: 0.01 and 0.05 mg kg^?1for organochlorines and 0.05 and 0.2 mg kg^?1for the pyrethroids. As blank sample, a sample of honey which did not contain detectable levels of the analytes sought was used. The validation study was in accordance to the DG SANCO guidelines. The scope of validation included recovery, linearity, limits of quantification and precision. Linearity is demonstrated all along the range of concentration that was investigated with correlation coefficients ≥0.98. Recoveries of the majority of compounds were in the 70%–120% range and were characterised by precision lower or equal to 20%. The validated method was used for a survey of 36 samples of honey produced in different areas of Cyprus and this is the first work on Cypriot honey samples investigating a broad range of pesticides. Only coumaphos was detected at concentrations higher than 0.01 mg kg^?1 in the 58.6% of the honey samples analysed for Coumaphos. The results were evaluated in accordance to the provisions of the Commission Regulation (EU) No 37/2010 on pharmacologically active substances and their classification regarding maximum residue limits (MRLs) in foodstuffs of animal origin. The concentrations of coumaphos in all positive samples were at levels much lower than the MRL.     

Fast and Selective Determination of Pesticides in Water by Automated On-Line Solid Phase Extraction Liquid Chromatography Tandem Mass Spectrometry

An automated on line-solid phase extraction (SPE) liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of 17 polar pesticides in water. Minimizing sample pretreatment and using a fast chromatographic separation, the method allowed a sample to be processed in 15 minutes. The MS analysis was performed by Data Dependent Acquisition, using the triggered Multiple Reaction Mode function that provided analyte confirmation, thus enhancing selectivity without compromising sensitivity. In fact, the optimized method enabled the determination of the considered pesticides at the ultratrace level, with detection limits in the range 0.07–1.65 ng/L (propazine and atrazine-desisopropyl, respectively); the only exception was linuron that showed a slightly higher detection limit (12.2 ng/L). The optimized method was then applied to real water samples; five pesticides were determined in river water, in the range 1.17–14.2 ng/L, while four were measured in drinking water, in the range 0.91–2.25 ng/L.     

高效液相色谱-串联质谱法测定粮谷中9种氨基甲酸酯类农药残留

本研究采用了高效液相色谱-串联质谱联用(HPLC-MS/MS)技术,建立了高灵敏度的同时检测粮谷中9种氨基甲酸酯类农药残留量的方法。样品经乙腈提取,中性氧化铝填充柱净化,然后采用HPLC-ESI( )-MS/MS测定。对液-质分离条件和样品前处理条件进行了优化。9种氨基甲酸酯类农药在0.1~100μg/L范围内线性良好,相关系数为0.9986~0.9998。在0.001~0.05mg/kg浓度范围内,平均加标回收率在73.40%~102.01%之间;相对标准偏差为1.25%~9.94%。该方法简便、快速、灵敏、净化效果好。可同时满足进、出口粮谷中多种氨基甲酸酯类农药残留量的检验工作需要。     

Determination of biotin following derivatization with 2-nitrophenylhydrazine by high-performance liquid chromatography with on-line UV detection and electrospray-ionization mass spectrometry

Currently, biotin is typically determined in Japan using a microbiological method. Such microbiological assays are sensitive, but they are not always highly specific and are also rather tedious and time-consuming. In the present study, RP-HPLC and LC-MS methods for the determination of biotin have been developed by derivatizing the carboxyl group with 2-nitrophenylhydrazine hydrochloride. 2-Nitrophenylhydrazine is used for the derivatization of carboxylic acids, and these derivatives are known to be applicable to LC-MS detection. Biotin in tablets were extracted by the addition of water and ultrasonic agitation. In order to clean up the sample solution, the filtrate was applied to an ODS cartridge and eluted with methanol. The conditions for preparing the 2-nitrophenylhydrazide derivatives were modified from a previous report for fatty acids. Good recovery rates of over 70% were obtained for the addition of 5-125 microg of biotin per formulation. The detection limit in HPLC at 400 nm was 0.6 ng per injection, with good linearity being obtained over the concentration range 0.001-0.2 microg per injection. Further, derivatives were determined by LC-MS with electrospray ionization, where the spectra indicated the molecular ions [M+H](+). The detection limit was 0.025 ng per injection in the selected ion monitoring analysis, and linearity was observed in the range of 0.6-6 ng per injection. The proposed method could be used to specifically determine the presence of biotin in relatively clean samples.     

Application of high-performance liquid chromatography–tandem mass spectrometry with a quadrupole/linear ion trap instrument for the analysis of pesticide residues in olive oil

This article describes the development of an enhanced liquid chromatography-mass spectrometry (LC-MS) method for the analysis of pesticides in olive oil. One hundred pesticides belonging to different classes and that are currently used in agriculture have been included in this method. The LC-MS method was developed using a hybrid quadrupole/linear ion trap (QqQ(LIT)) analyzer. Key features of this technique are the rapid scan acquisition times, high specificity and high sensitivity it enables when the multiple reaction monitoring (MRM) mode or the linear ion-trap operational mode is employed. The application of 5 ms dwell times using a linearly accelerating (LINAC) high-pressure collision cell enabled the analysis of a high number of pesticides, with enough data points acquired for optimal peak definition in MRM operation mode and for satisfactory quantitative determinations to be made. The method quantifies over a linear dynamic range of LOQs (0.03-10 microg kg(-1)) up to 500 microg kg(-1). Matrix effects were evaluated by comparing the slopes of matrix-matched and solvent-based calibration curves. Weak suppression or enhancement of signals was observed (<15% for most-80-of the pesticides). A study to assess the identification criteria based on the MRM ratio was carried out by comparing the variations observed in standard vs matrix (in terms of coefficient of variation, CV%) and within the linear range of concentrations studied. The CV was lower than 15% when the response observed in solvent was compared to that in olive oil. The limit of detection was < or =10 microg kg(-1) for five of the selected pesticides, < or =5 microg kg(-1) for 14, and < or =1 microg kg(-1) for 81 pesticides. For pesticides where additional structural information was necessary for confirmatory purposes-in particular at low concentrations, since the second transition could not be detected-survey scans for enhanced product ion (EPI) and MS3 were developed.     

QuEChERS-液相色谱-串联质谱法同时测定果蔬中16种农药残留

建立了果蔬中吡虫啉、咪鲜胺、苯醚甲环唑、嘧菌酯、噻虫嗪等16种常见农药多残留的液相色谱-串联质谱(LC-MS/MS)分析方法。以乙腈为提取剂,样品经高速匀浆方法提取后,提取液采用液-液萃取静置分层,取上清液进行净化处理。比较了石墨化碳-氨基复合固相萃取与QuEChERS两种不同净化技术的净化效果,最终确定采用QuEChERS方法为净化手段。即提取液经装有150 mg N-丙基乙二胺(PSA)填料、900 mg无水硫酸镁的净化管净化,除去样品中大部分的色素及有机酸等干扰基质,再经LC-MS/MS分析,有效地降低了样品中的复杂基质所带来的背景干扰。加标水平为5、10、20 μg/kg时,16种农药的平均回收率为75%~111%,相对标准偏差小于16%。16种农药的检出限为0.2~5 μg/kg。采用LC-MS/MS定性分析、基质匹配标准曲线法定量分析,线性关系和回收率结果均令人满意。实验证明,建立的QuEChERS净化与LC-MS/MS相结合的检测方法具有快速、准确、灵敏度高等优点,能够准确测定果蔬中16种农药残留。     

Determination of polar organophosphorus pesticides in aqueous samples by direct injection using liquid chromatography-tandem mass spectrometry

It was demonstrated that four out of six of the very polar organophosphorus pesticides (OPs), i.e. acephate, methamidophos, monocrotophos, omethoate, oxydemeton-methyl and vamidothion, could not be extracted from water using commonly available SPE cartridges. In addition, GC analysis on all six compounds was found to be troublesome due to their polar and thermolabile character. This initiated the development of an alternative highly sensitive and selective method for the determination of the above mentioned very polar OPs in water, based on LC-MS. Large volume (1 ml) water samples were directly injected onto an RP18 HPLC column with a polar endcapping. The latter was essential for obtaining retention and maintaining column performance under 100% aqueous conditions during the sampling. The compounds were ionized using atmospheric pressure chemical ionization and detected on a tandem mass spectrometer operated in multiple reaction-monitoring mode. The detection limits were in the range of 0.01-0.03 microg/l. Compared to conventional GC methods, the developed LC-MS procedure is very straightforward, fast and more reliable. This application demonstrates the applicability of LC-MS for analysis of polar OPs in surface, ground and drinking water, as a more favourable alternative to GC.     

LC-MS/MS法同时测定4种中草药中155种农药残留

建立了液相色谱-串联质谱(LC-MS/MS)同时测定4种中草药(甘草、银杏叶、菊花和八角茴香)中155种农药残留方法。样品采用乙腈、无水硫酸镁和乙酸钠分散固相萃取(DSPE),再经Cleanert TPH固相萃取(SPE)柱净化,乙腈/甲苯(8:1,V/V)洗脱,液相色谱串联质谱多反应监测模式下测定,外标法定量。实验结果表明,155种农药的检出限(S/N=3)和定量限(S/N=10)范围分别为0.4～34.1μg/kg和1.3～113.7μg/kg;在1.0～2400.0μg/kg浓度范围内,155种农药中有148种农药在4种中草药中线性相关系数平均值R2≥0.9950;在低、中、高3个添加水平,86.5%～97.4%的农药平均回收率在60%～120%范围,94.2%～100.0%的农药相对标准偏差RSD≤20%(n=5)。该方法适用于中草药中农药多残留检测。     

Determination of 48 pesticides and their main metabolites in water samples by employing sonication and liquid chromatography-tandem mass spectrometry

In this work, a rapid and sensitive analytical multiresidue method has been developed for the simultaneous determination of 48 pesticides and 19 metabolites in waters (tap, leaching and sewage), using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with triple quadrupole in selected reaction monitoring (SRM) mode. The procedure involves initial single phase extraction of samples with acetonitrile by sonication, followed by liquid-liquid partition aided by “salting out” process using NaCl. Matrix influence on recoveries was evaluated for the three waters. More than 50% of the compound presented very low signal suppression. The method presents good linearity over the range assayed 10-500 μg L⁻¹ and the most frequent detection limits was 0.05 ng mL⁻¹. The average recovery by the LC-MS/MS method obtained for these compounds varied from 74.6 to 111.2% with a relative standard deviation between 2.5 and 8.9%. The proposed method was used to determine pesticides levels in leaching water samples from 5 lysimeters from an experimental greenhouse located in Murcia.     

Simultaneous determination of carbamate and organophosphorus pesticides in fruits and vegetables by liquid chromatography-mass spectrometry

A liquid chromatography-mass spectrometry (LC-MS) method was established for the purpose of simultaneous determination of carbamate and organophosphorus (OPPs) pesticides in fruits and vegetables. Samples were extracted with acetonitrile; and then prepared by dispersive solid-phase extraction (dispersive-SPE) with primary secondary amine (PSA) as the sorbent. Four common representative samples (tomato, apple, carrot, and cabbage) were selected from the supermarket to investigate the effect of different matrices on pesticides recoveries and assay precision after spiking samples with 0.05 mg/kg. Matrix composition did not interfere significantly with the determination of the pesticides. The obtained recoveries were, with a few exceptions, in the range of 70-110% with RSDs less than 8%. It was applied to pesticide residue monitoring in vegetables and fruits from local markets.     

固相萃取-液相色谱-串联质谱法测定蔬菜中4种有机磷农药及其代谢产物

在蔬菜种植中经常使用的有机磷农药马拉硫磷、甲基对硫磷、敌百虫及乙酰甲胺磷可能转化的主要代谢产物分别为O,O-二甲基二硫代磷酸酯、对硝基酚、敌敌畏及甲胺磷。根据蔬菜色素等基质的含量不同采用不同的净化方法,色素含量高的蔬菜采用活性炭和弗罗里硅土串联固相萃取小柱净化,其他蔬菜采用弗罗里硅土固相萃取小柱净化。色谱分离选择ACQUITY UPLC BEH HILIC色谱柱,以乙腈和5 mmol/L乙酸铵水溶液为流动相进行梯度洗脱,得到的分离效果较好;质谱采用电喷雾正或负离子电离、多反应监测模式检测。液相色谱-质谱检测的基质效应为15.3%~45.1%;4种有机磷农药及其代谢物的方法回收率为76.9%~102.8%,相对标准偏差为5.92%~10.19%;定量限范围为0.001~0.01 mg/L;在0.01~1.00 mg/L范围内线性相关系数为0.9982~0.9999。方法具有良好的回收率、相对标准偏差、定量限及线性关系,适合蔬菜中有机磷及代谢物的检测,应用该检测方法对农贸市场购买的白菜、辣椒、西红柿及洋葱进行了检测。     

Comprehensive multi-residue method for the target analysis of pesticides in crops using liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS) multi-residue method for the simultaneous target analysis of a wide range of pesticides and metabolites in fruit, vegetables and cereals has been developed. Gradient elution has been used in conjunction with positive mode electrospray ionization tandem mass spectrometry to detect up to 171 pesticides and/or metabolites in different crop matrices using a single chromatographic run. Pesticide residues were extracted/partitioned from the samples with acetone/dichloromethane/light petroleum. The analytical performance was demonstrated by the analysis of extracts from lettuce, orange, apple, cabbage, grape and wheat flour, spiked at three concentration levels ranging from 0.01 to 0.10 mg/kg for each pesticide and/or metabolite. In general, recoveries ranging from 70 to 110%, with relative standard deviations better than 15%, were obtained. The recovery and repeatability data are in good accordance with EU guidelines for pesticide residue analysis. The limit of quantification for all targeted pesticides and metabolites tested was 0.01 mg/kg. The selectivity and robustness of the LC-MS/MS method was demonstrated by a 1-year comparison of its analytical results with those obtained from our validated GC and LC multi-residue methods applied to more than 3500 routine samples. The validated LC-MS/MS method has been implemented in our analytical scheme since 2004, replacing four of the conventional detection methods, i.e. GC-flame-photometric detection (acephate, methamidophos, etc.), GC-nitrogen-phosphorus detection, LC-UV detection (carbendazim, thiabendazole, imazalil and prochloraz) and LC-fluorescence detection (N-methylcarbamate pesticides). During a 3-year period, the LC-MS/MS method has been applied to the analyses of more than 12,000 samples.     

Sample treatment and determination of pesticide residues in fatty vegetable matrices: A review

A demanding task in pesticide residue analysis is yet the development of multi-residue methods for the determination of pesticides in vegetables with relatively high fat content (i.e. edible oils and fatty vegetables). The separation of pesticides and other chemical contaminants from high-fat food samples prior to subsequent steps in the analytical process is yet a challenging issue to which much effort in method development has being applied. This review addresses the main sample treatment methodologies for pesticide residue analysis in fatty vegetable matrices. Even with the advent of advanced hyphenated techniques based on mass spectrometry these complex fatty matrices usually require extensive sample extraction and purification. Current methods involve the use of one or the combination of some of the following techniques for both the sample extraction and clean-up steps: liquid-liquid partitioning, solid-phase extraction (SPE), gel-permeation chromatography (GPC), matrix solid-phase dispersion (MSPD), etc. An overview of methods developed for these contaminants in fatty vegetables matrices is presented. Sample extraction and purification techniques are discussed and their most recent applications are highlighted. This review emphasizes that sample preparation is a critical step, but also the determination method is, and cannot be treated separately from sample treatment. In recent years, the appearance and use of new, more polar pesticides has fostered the development of liquid chromatography/mass spectrometry (LC-MS) besides gas chromatography. The main features of LC-MS for the analysis of multi-class pesticides in fatty vegetable samples will be also underlined, with an emphasis on the multi-class, multi-residue strategy and the difficulties associated.     

Application of liquid chromatography with mass spectrometry combined with photodiode array detection and tandem mass spectrometry for monitoring pesticides in surface waters

Liquid chromatography with photodiode array detection (LC-DAD) and liquid chromatography with mass spectrometry (LC-MS) are two techniques that have been widely used in monitoring pesticides and their degradation products in the environment. However, the application of liquid chromatography with tandem mass spectrometry (LC-MS-MS) for such purposes, once considered too costly, is now gaining considerable ground. In this study, we compare these methods for the multi-residue analysis of pesticides in surface waters collected from the central and southeastern regions of France, and from the St. Lawrence River in Canada. Forty-eight pesticides belonging to eight different classes (triazine, amide, phenylurea, triazole, triazinone, benzimidazole, morpholine, phenoxyalkanoic), along with some of their degradation products, were monitored on a regular basis in the surface waters. For LC-MS, we used the electrospray ionization (ESI) interface in the negative ionization mode on acidic pesticides (phenoxyalkanoic, sulfonylurea), and the atmospheric pressure chemical ionization (APCI) interface in the positive ionization mode on the remaining chemicals. Different extraction techniques were employed, including liquid-liquid extraction with dichloromethane, and solid-phase extraction using C18-bonded silica and graphitized carbon black cartridges. Eleven of the target chemicals (desethylatrazine, desisopropylatrazine, atrazine, simazine, terbuthylazine, metolachlor, carbendazime, bentazone, penconazole, diuron and isoproturon) were detected by LC-MS at concentrations ranging from 20 to 900 ng/l in the surface waters from France, and six pesticides (atrazine, desethylatrazine, desisopropylatrazine, cyanazine, simazine and metolachlor) were detected by LC-MS and LC-MS-MS at concentrations ranging from 3 to 52 ng/l in the samples drawn from the St. Lawrence River. There was good correlation between the LC-DAD and LC-MS techniques for 60 samples. The slope of the curves expressing the relationship between the results obtained with LC-DAD versus those obtained by LC-MS was near 1, with a correlation coefficient (r) of over 0.93. The identification potential of the LC-MS technique, however, was greater than that of the LC-DAD; its mass spectra, mainly reflecting the pseudomolecular ion resulting from a protonation or a deprotonation of the molecule, was rich in information. The LC-MS-MS technique with ion trap detectors, tested against the LC-MS on 10 surface water samples, gave results that correlated well with the LC-MS results, albeit generating mass spectra that yielded far more information about the structure of unknown substances. The sensitivity of the LC-MS-MS was equivalent to the selected ion monitoring (SIM) acquisition mode in LC-MS. The detection limits of the target pesticides ranged from 20 to 100 ng/l for the LC-MS technique (under full scan acquisition), and from 2 to 6 ng/l for LC-MS-MS. These limits were improved by a factor of almost 10 by increasing the sample volume to 10 l.     

Multi-residue analytical methods for the determination of pesticides and PPCPs in water by LC-MS/MS: a review

Residues of pesticides, pharmaceutical and personal care products (PPCPs) are contaminants of world-wide concern. Consequently, there is a growing need to develop reliable analytical methods, which enable rapid, sensitive and selective determination of these pollutants in environmental samples, at trace levels. In this paper, a review of the liquid chromatography-tandem mass spectrometry (LC-MS/MS) based methods for the determination of pesticides and PPCPs in the environment is presented. Advanced aspects of current LC-MS/MS methodology, including sample preparation and matrix effects, are discussed.     

Simple and rapid screening procedure for pesticides in water using SPE and HPLC/DAD detection

An HPLC method, using a photodiode array detector (DAD) has been developed for the simultaneous screening of pesticides. A solid phase extraction system (SPE) has been combined, off-line, with the HPLC/DAD to isolate, recover and quantify pesticides from water samples at ppb levels. The pesticides are eluted from a Hypersil C₁₈ column 5 μm applying a solvent elution programme with two steps, isocratic and gradient mode, in reverse phase. Full UV spectra from 200 to 400 nm are recorded on-line during the analysis and may be compared to stored spectra. The method has been applied to the determination of pesticides in real water samples.