Simultaneous determination of base/neutral and acid herbicides in natural water at the part per trillion level

Summary A new method for the simultaneous identification and quantification of base/neutral and acidic pesticides at a low nanogram per liter concentration level in natural waters is presented. The method includes enrichment of the compounds by solid phase extraction on graphitized carbon black, followed by sequential elution of the base/neutral and acidic pesticides. Identification and quantification of the compounds is performed with HPLC-ESI-MS. This procedure involves passing 1 L of ground water and 2 L of drinking water samples through a 0.5 g graphitized carbon black (GCB) extraction cartridge. A conventional 4.6-mm-i.d. reversed phase LC C-18 operating with a 1 mL min⁻¹ flow of the mobile phase was used to chromatograph the analytes. A flow of 100 μL min⁻¹ of the column effluent was diverted to the ESI source. The ESI source was operated in positive ion mode for base/neutral pesticides and in negative-ion mode for acid pesticides. For the analyte considered, the response of the mass detector was linearly related to the amount of the analytes injected between 5 and 250 ng. In all cases, recoveries of the analytes were better than 90%. The limit of detection (signal-to-noise ratio=3) of the method for the pesticides considered in drinking water samples was estimated to be about 3–10 ng L⁻¹.     

Simultaneous determination of acidic and non-acidic pesticides in natural waters by liquid chromatography-mass spectrometry

There is increasing interest and demand for real multi-residue methods able to simultaneously determine pesticides with a broad spectrum of chemical characteristics in environmental and biological matrices. A method based on solid-phase extraction with a Carbograph 4 cartridge and liquid chromatography with electrospray mass spectrometry (LC-ES-MS) enabling simultaneous determination of non-acidic and acidic pesticides in real water samples is described. On repeatedly (n=5) extracting 4 l of drinking water (spike level 50 ng/l), 2 l of ground water (spike level 100 ng/l) and 1 l of river water (spike level 200 ng/l), recovery of 26 base/neutral pesticides and 13 acidic pesticides were equal to or better than 80%, except for carbendazim (67%), butocarboxim (73%), aldicarb (75%) and molinate (77%). Relative standard deviations ranged between 4 and 15%. Final extracts containing acidic and non-acidic pesticides were analyzed in a single chromatographic run while the ES-MS system was operated in both positive and negative ion modes. With the aim of finding the best operating conditions, in terms of sensitivity, the pH of the LC eluent was varied in the 2.9-8.4 range. Altogether, the best results were obtained by using an LC eluent containing 1 mmol/l formic acid. Over the entire pH range considered, well shaped peaks for both basic and acidic analytes were achieved by the use of a new generation LC column. By extracting selected ion current profiles from the total ion current mass chromatogram relative to analysis of 4 l of drinking water spiked with 50 ng/l of each of the 39 analytes, estimated limits of detection ranged between 0.05 and 1.5 ng/l, except for propyzamide (8 ng/l) and 2,4-DB (3 ng/l).     

Simultaneous quantification of neutral and acidic pharmaceuticals and pesticides at the low-ng/l level in surface and waste water

A new analytical method is presented that allows simultaneous determination of neutral and acidic pharmaceuticals and pesticides in natural waters. The compounds investigated include frequently used pharmaceuticals, i.e., the anti-epileptic carbamazepine, four analgesic/anti-flammatory drugs (ibuprofen, diclofenac, ketoprofen and naproxen) and the lipid regulator clofibric acid and important pesticides including triazines, acetamides and phenoxy acids. Sample enrichment was achieved in one step with a newly developed solid-phase extraction procedure using the Waters Oasis HLB sorbent. The neutral compounds were analyzed by GC-MS in a first step, and then the acidic compounds after derivatization with diazomethane. Relative recoveries using isotope labeled internal standards were between 71 and 118% and the detection limits were in the range of 1 to 10 ng/l in drinking water, surface water and waste water treatment plant effluents (precision: 1-15%). The developed analytical method proved to be very durable during a 3-month field study and the target analytes were detected in concentrations of 5-3,500 ng/l in waste water treatment plant effluents, river water and lake water.     

Multiresidue Analysis of Pesticides in Water from Rice Cultures by On-line Solid Phase Extraction Followed by LC-DAD

Abstract

An automated on-line solid phase extraction procedure followed by liquid chromatography with diode array detection was investigated for the determination of different classes of pesticides in water samples containing varied amount of humic substances. The different pesticides used were: carbendazin, carbofuran, atrazine, diuron, propanil, molinate, alachlor, parathion-ethyl, diazinon, trifluralin and the degradation products deisopropylatrazine and deethylatrazine. Humic substances extracted from a Brazilian sediment were used from 5 to 80 mg/l and their influence on recoveries was evaluated in neutral and acidic media. Recoveries higher than 70% were obtained for all the pesticides, from the preconcentration of 75 ml of aqueous sample fortified at 2 ng/ml using precolumns packed with PLRP-S. Good recoveries were obtained at neutral pH for most of the analytes up to 40 mg/l of humic acid. Only at 80 mg/l the recoveries were significantly affected, both at acidic and neutral pH. The method was applied to the determination of pesticides in river water spiked at 0.1 to 1 ng/ml. Detection limits obtained for water containing 10 mg/l of humic acid were between 0.05 and 0.3 ng/ml.     

Determination of trace amounts of off-flavor compounds in drinking water by stir bar sorptive extraction and thermal desorption GC-MS.

A method for the determination of trace amounts of off-flavor compounds including 2-methylisoborneol, geosmin and 2,4,6-trichloroanisole in drinking water was developed using the stir bar sorptive extraction technique followed by thermal desorption-GC-MS analysis. The extraction conditions such as extraction mode, salt addition, extraction temperature, sample volume and extraction time were examined. Water samples (20, 40 and 60 ml) were extracted for 60-240 min at room temperature (25 degrees C) using stir bars with a length of 10 mm and coated with a 500 microm layer of polydimethylsiloxane. The extract was analyzed by thermal desorption-GC-MS in the selected ion monitoring mode. The method showed good linearity over the concentration range from 0.1 or 0.2 or 0.5 to 100 ng l(-1) for all the target analytes, and the correlation coefficients were greater than 0.9987. The detection limits ranged from 0.022 to 0.16 ng l(-1). The recoveries (89-109%) and precision (RSD: 0.80-3.7%) of the method were examined by analyzing raw water and tap water samples fortified at the 1 ng l(-1) level. The method was successfully applied to low-level samples (raw water and tap water).     

Determination of quinolones in water samples by solid-phase extraction and liquid chromatography with fluorimetric detection

A method is reported for the determination, in water samples, of 10 quinolones which are used as veterinary drugs. Analytes are isolated from samples by solid-phase extraction (SPE) and analysed by reversed-phase high-performance liquid chromatography using fluorimetric detection. A solid-phase extraction procedure based on retention on HBL OASIS cartridges and elution with a mixture of acetonitrile-water in basic medium is suitable for pre-concentration of the analytes. Pre-concentration factors up to 250 can be obtained. The quinolones are separated with an octyl silica-based column and mobile phases consisting of aqueous oxalic acid solutions and acetonitrile mixtures. The attained detection limits of the whole process are in the ng l(-1) level when 250 ml of water sample is processed. Recovery rates, from natural water samples spiked at 2060 ng l(-1) level, range from 70 to 100% and common standard deviation are about 6-12%.     

Determination of organophosphorous pesticides in the ppq range using a simple solid-phase extraction method combined with dispersive liquid-liquid microextraction

Solid-phase extraction combined with dispersive liquid-liquid microextraction (SPE-DLLME) was applied for the extraction of six organophosphorous pesticides (OPPs) in water samples. The analytes considered in this study were determined by gas chromatography with mass spectrometry and included prophos, diazinon, chlorpyrifos methyl, methyl parathion, fenchlorphos and chlorpyrifos. Several extraction conditions (extraction solvent and elution/dispersion solvents nature, extraction solvent volume, elution solvent volume, water volume and sample volume) were tested for SPE-DLLME with these analytes and the best results were obtained using carbon tetrachloride as the extraction solvent and acetone as the elution/dispersion solvent. Calibration curves for the determination of OPPs in water samples were constructed in the concentration range of 10-100 ng/L. Limits of detection (LODs) ranged from 38 to 230 pg/L values that are below the maximum admissible level for drinking water (100 ng/L). Relative standard deviations (RSD) were between 8.6 and 10.4% for a fortification level of 100 ng/L. At the same fortification level, the relative recoveries (R.R.) of tap, well and irrigation water samples were in the range of 30.2-97.1%.     

Validated dispersive liquid-liquid microextraction for analysis of organophosphorous pesticides in water

Dispersive liquid-liquid microextraction (DLLME) combined with gas chromatography and mass spectrometry (GC-MS) was applied to the determination of six organophosphorous pesticides (OPPs) in water samples. The analytes included in this study were prophos, diazinon, chlorpyrifos methyl, methyl parathion, fenchlorphos and chlorpyrifos. Several extraction and dispersion solvents were tested for dispersive liquid-liquid microextraction of these analytes and the best results were obtained using chloroform as extraction solvent and 2-propanol as dispersion solvent. Calibration curves of the analytes in water samples were constructed in the concentration range from 100 to 1100 ng/L for prophos, diazinon and methyl parathion and in the range from 100 to 1000 ng/L for chlorpyrifos methyl, fenchlorphos and chlorpyrifos. Limits of detection (LODs) were in the range of 1.5-9.1 ng/L and limits of quantification (LOQs) were in the range of 5.1-30.3 ng/L, below the maximum admissible level for drinking water. Relative standard deviations (RSDs) were between 6.5 and 10.1% in the concentration range of 100-1000 ng/L. The relative recoveries (%RRs) of tap, well and irrigation water samples fortified at 800 ng/L were in the range of 46.1-129.4%, with a larger matrix effect being detected in tap water.     

Rapid gas chromatography-mass spectrometry screening method for human pharmaceuticals, hormones, antioxidants and plasticizers in water

A rapid gas chromatography-mass spectrometry (GC-MS) method was developed and validated allowing quantification at the ng/l level of 19 analytes in water including human pharmaceuticals, hormones, antioxidants and a plasticizer. On-line continuous liquid-liquid extraction with dichloromethane of 10-401 unfiltered water samples was used to achieve a 10000-40000-fold concentration factor. No sample cleanup or derivatization was required. Recoveries ranged from 57 to 120%. Application of the method to water recycling plant effluent demonstrated the presence of nearly all targeted compounds at ng/l to microgram/l levels. Screening for nontarget compounds in the treated effluent samples indicated the method could be readily extended to include additional analytes.     

Quantification and confirmation of anionic, cationic and neutral pesticides and transformation products in water by on-line solid phase extraction-liquid chromatography-tandem mass spectrometry

Two on-line SPE-LC-ESI-MS/MS methods have been developed for the rapid determination and confirmation of 18 polar pesticides and nine transformation products (TPs) in water samples. Given the very different physico-chemical characteristics of the analytes, it was not feasible the simultaneous determination of all selected compounds in only one method. Thus, it was necessary to use heptafluorobutyric acid and formic acid in order to obtain good retention in the SPE cartridge for basic and acidic analytes, respectively. The developed analytical methodology based on the direct injection of 2 mL of water sample in the system allowed the quantification of all analytes at the 25 ng/L level (LOQ) with limits of detection normally lower than 5 ng/L. Satisfactory recoveries (70-110%) were obtained for most compounds in ground and surface water samples. Some exceptions were found mainly in surface water, due to the ion suppression produced by the higher amount of matrix interferents in these samples. The acquisition of two MS/MS transitions for each compound allowed the reliable confirmation of positive findings even at the LOQ level. The developed methodology was applied to real ground and surface water samples showing the interest of including TPs in monitoring methods, as several of them were found at concentrations higher than that of parent compounds.     

Simultaneous analysis of neutral and acidic pharmaceuticals as well as related compounds by gas chromatography-tandem mass spectrometry in wastewater

This work presents a new multi-residue analytical method based on solid phase extraction (SPE) with Oasis HLB sorbent, followed by gas chromatography tandem mass spectrometry (GC-MS/MS) for the simultaneous determination of a group of 10 acidic and neutral pharmaceuticals and related compounds in wastewaters. The typical derivation step was avoided, allowing the determination of acidic and neutral pollutants in a single analysis as well as providing a fast and easy method suitable for routine monitoring. Target pollutants include: anti-inflammatory drugs (ibuprofen, acetaminophen and diclofenac); an antiepileptic agent (carbamazepine); stimulants (caffeine and nicotine); an antiseptic (triclosan); a plasticizer (bisphenol A) and two of their more relevant metabolites (2,8-dichlorodibenzo-p-dioxin and 1,7-dimethylxanthine). Recoveries between 66 and 112% were achieved for all the target compounds (except for 2,8-dichlorodibenzo-p-dioxin). Good linearity was observed within the studied ranges (R² > 0.993). Acceptable intra and inter-day precision was obtained, with relative standard deviation between 2 and 18%. The application of the optimized MS/MS mode allowed method detection limits in the range of 0.2-16 ng/L, with the exception of ibuprofen (120 ng/L). Finally, the methodology was successfully applied to the analysis of hospital effluent samples. All target analytes were detected at concentrations between 1 ng/L and 83215 μg/L. Even in the absence of derivatization, all the analytes showed good peak shape, except acetaminophen, which exhibited peak tailing. However, the method proved to be repetitive and reproducible, and the peak shape did not represent a problem for the reliable quantification of this compound. For most of the analytes studied, the detection limits achieved compare well against values reported in previously published methods.     

Use of self-plasticizing EVA membrane for potentiometric anion detection

A method based on solid-phase microextraction and gas chromatography flame photometric detector for the determination of organophosphorous pesticides (OPPs) in aqueous samples was described. Five kinds of commercially available fibers-7, 30 and 100 mum PDMS, 85 mum PA and 65 mum PDMS-DVB-were compared and 100 mum PDMS and 85 mum PA were the most sensitive fiber coatings for the analytes. The extraction time, extraction temperature, pH and content of NaCl were found to have significant influence on extraction efficiency. The optimized conditions were 100 mum PDMS fiber, 30 min extraction time at 40 degrees C, with 3% NaCl content and no pH adjustment. The linear range was 0.5-100 mug l(-1) for most of the analytes. The limits of detection (LODs) ranged from 0.049 mug l(-1) (for parathion) to 0.301 mug l(-1) (for carbophenothion) and RSD% of repeatability at the 10 mug l(-1) level were all below 8%. Environmental water samples were analyzed, but none of the analytes was detected. The recovery of spiked water samples was from 75.3 to 102.6%.     

Measurement uncertainty arising from trueness of the analysis of two endocrine disruptors and their metabolites in environmental samples. Part II. Solid-phase extraction from environmental natural waters

In this work, a preconcentration method for the simultaneous determination of the endocrine disrupting chemicals (EDCs), diuron (1-(3,4-dichlorophenyl)-3,3-dimethylurea), and linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea), as well as their metabolites DCPU (1-(3,4-dichlorophenyl) urea), DCPMU (1-(3,4-dichlorophenyl)-3-methylurea) and 3,4-DCA (3,4-dichloroaniline), present in natural waters was optimized and validated. Water was subjected to solid-phase extraction (SPE) and the influence of several experimental variables affecting the extraction efficiency of the target analytes was studied, including the sorbent material, elution solvents, pH and breakthrough volume, as well as some solution parameters that is, ionic strength and organic matter content. A high-performance liquid chromatography system coupled to UV-diode array detector (DAD) was used for the target analytes quantification at the optimum conditions described in Part I. The fully nested experimental design, adapted to the new experimental parameters, was used to study the measurement uncertainty arising from trueness by estimating proportional bias (in terms of recovery). The overall recoveries of the target analytes were in the range of 71.6-90.2%, except 3,4-DCA for which a low overall recovery of 51.4% was obtained. The analytical procedure was shown to be linear over the studied range of concentration (25-400 ng/l), exhibiting satisfactory repeatability and reaching limits of detection in the 1.3-11.2 ng/l range for all, quite different in nature, water types. The SPE method was further applied for the determination of the selected EDCs and their metabolites in water samples taken from selected study stations in the region of Epirus (N.W. Greece) corresponding to the sediment samples locations (Part I).     

Solid-phase microextraction with on-fiber derivatization for the analysis of anti-inflammatory drugs in water samples

A sensitive and solvent-free procedure for the determination of non-steroidal acidic anti-inflammatory drugs in water samples was optimized using solid-phase microextraction (SPME) followed by on-fiber silylation of the acidic compounds and gas chromatography-mass spectrometry (GC-MS) determination. Microextraction was carried out directly over the filtered water samples using a polyacrylate fiber. Derivatization was performed placing the SPME fiber, loaded with the extracted analytes, in the headspace of a vial containing 50 microl of N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA). Derivatives were desorbed for 3 min in the GC injector. Influence of several parameters in the efficiency of microextraction (volume of sample, time, pH, type of fiber coating, etc.) and derivatization steps (time, temperature and volume of MTBSTFA) was systematically investigated. In the optimal conditions an excellent linearity over three orders of magnitude and quantification limits at the ng/l level (from 12 to 40 ng/l) were achieved. The proposed method was applied to the determination of acidic compounds in sewage water and results compared to those obtained using solid-phase extraction (SPE) followed by the derivatization of the compounds in the organic extract of the solid-phase extraction cartridge.     

Determination of acidic drugs and caffeine in municipal wastewaters and receiving waters by gas chromatography-ion trap tandem mass spectrometry

Some aspects of both sample preparation and instrumental techniques for analysis of such acidic drugs as acetylsalicylic acid, ibuprofen, gemfibrozil, fenoprofen, naproxen, ketoprofen, and diclofenac, as well as caffeine in surface water and municipal wastewater have been studied and further developed. Water samples were filtered and target analytes were extracted by solid-phase extraction (SPE). Supelco LC-18 and Oasis HLB SPE cartridges were used to pre-concentrate samples for acidic drugs and caffeine, respectively. A methylation process was applied to acidic drugs prior to analysis while caffeine was analyzed directly. A method of gas chromatography-ion trap tandem mass spectrometry (IT-MS/MS) for analysis of the target acidic pharmaceuticals and caffeine is presented here in detail. Such parameters as collision-induced dissociation (CID) voltage, isolation time, excitation time, excitation storage level, and electron energy were adjusted in order to optimize the instrument analytical performance. After optimization, an instrument detection limit of 0.5-20 pg/microL with signal-to-noise (S/N) not less than 5 was achieved for all target analytes. It was shown that this method has good linearity within the range of 10-2000 pg/microL. The application of the optimized IT-MS/MS parameters conjointly with the sample preparation procedure resulted in method detection limits (MDLs) of 0.1-1.0 and 20 ng/L for the determination of acidic drugs and caffeine, respectively in such samples as surface water, effluent from municipal wastewater plants, as well as receiving waters.     

Analysis of perfluorooctanesulfonate and related fluorochemicals in water and biological tissue samples by liquid chromatography-ion trap mass spectrometry

A method for the determination of perfluorinated compounds (PFCs) in various water and biological tissue samples was developed and validated. The contents of selected PFCs (i.e., perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA) and perfluorodecanoate (PFDA)) in water samples were extracted by the C(18) solid-phase extraction (SPE). The biological tissue samples (frozen-dried fish and oysters) were simply extracted by liquid-solid extraction with MTBE and adding tetrabutylammonium hydrogensulfate (TBA) as an ion-pairing reagent. The analytes were then identified and quantitated by liquid chromatography-ion trap negative electrospray mass spectrometry (LC-ESI ion-trap-MS). Limits of quantitation (LOQ) were established between 0.5 and 6 ng/l in 250 ml of water sample, while 5-50 ng/g (dry weight) for biological tissue sample. Intrabatch and interbatch precision with their accuracy at two concentration levels were also investigated. Precision for these three PFCs, as indicated by RSD, proved to be less than 11 and 17%, respectively. The total contents of PFOA, PFOS and PFDA were detected in concentrations of up to 400 ng/l in various water samples, while up to 1,100 ng/g in fish and oyster samples. PFOA and PFDA was the major PFCs detected in water samples and biological tissue samples, respectively.     

Extraction and analysis of pharmaceuticals in polluted sediment using liquid chromatography mass spectrometry

A multi-residue method for the extraction and clean-up of sediment samples was developed for the analysis of pharmaceutical residues. Sediment samples were collected in the proximity of sewage water plant in Stockholm, Sweden. Target analytes were the basic β-blocker propranolol, the neutral neuroleptic carbamazepine and the acidic anticoagulant warfarin, the painkiller diclofenac and the lipid regulator gemfibrozil. The extraction solvent was optimised with regard to pH and organic modifer. Extraction and clean up were performed with liquid-liquid extraction and ultra-sonication followed by solid-phase extraction. One extraction solvent, containing acetone/McIlvaine buffer pH4, provided satisfactory extraction for all substances. LC/MSMS in the MRM mode was used for determination. The recoveries of the extraction and clean-up steps were 60–75% (±2–8%) and LOQs were in the range 0.4–8?ng/g sediment (dry weight). The pharmaceuticals found in the sediment samples were propranolol and carbamazepine, representing substances with basic and neutral properties. Additionally, the samples were analysed with LC/QTOF for verification with the use of accurate mass measurement in the full-scan mode. Pharmaceuticals not represented in the original method were looked for. Non-target pharmaceuticals found using the LC/QTOF system were the basic β-blocker metoprolol and the acidic painkiller naproxen.     

Liquid chromatography/electrospray ionization tandem mass spectrometric screening and confirmation methods for beta2-agonists in human or equine urine

Electrospray ionization (ESI) mass spectra of 19 common beta(2)-agonists were investigated in terms of fragmentation pattern and dissociation behavior of the analytes, proving the origin of fragment ions and indicating mechanisms of charge-driven and charge-remote fragmentation. Based on these data, liquid chromatographic/ESI tandem mass spectrometric (LC/ESI-MS/MS) screening and confirmation methods were developed for doping control purposes. These procedures employ established sample preparation steps including either acidic or enzymatic hydrolysis, alkaline extraction and, in the case of equine urine specimens, acidic re-extraction of the analytes. In addition, a degradation product of formoterol caused by acidic hydrolysis during sample preparation could be identified and utilized as target compound in screening and also confirmation methods. The screening procedures cover 18 or 19beta(2)-agonists, the estimated limits of detection of which for equine and human urine samples vary between 2 and 100 ng ml(-1) and between 2 and 50 ng ml(-1), respectively. A single LC/MS/MS analysis can be performed in 9 min.     

Speciation of butyl and phenyltin compounds using dispersive liquid-liquid microextraction and gas chromatography-flame photometric detection

Dispersive liquid-liquid microextraction and gas chromatography-flame photometric detection (DLLME-GC-FPD) were performed for the speciation of butyl and phenyltin compounds in water samples after derivatization with sodium tetraethylborate (NaBEt4). Some important parameters, such as pH, amount of NaBEt4, derivatization time, kind and volume of extraction and disperser solvents, extraction time and salt effect were investigated and optimized. High enrichment factors (825-1036) and low detection limits (0.2-1 ng L(-1)) were obtained under the optimum conditions. The calibration graphs were linear in the range of 0.5-1000 ng L(-1) (as Sn) for the target analytes. The relative standard deviations (RSDs) for the extraction of 20 ng L(-1) (as Sn) of butyl and phenyltin compounds varied from 2.3 to 5.9% (n=7) and from 4.1 to 8.8% (n=7) with and without using internal standard, respectively. Seawater and river water samples were successfully analyzed using the proposed method and the relative recoveries of the studied compounds in the water samples, at spiking levels of 10.0 and 100 ng L(-1) (as Sn) were obtained to be 82.5-104.7%.     

Determination of polar pesticides with atmospheric pressure chemical ionisation mass spectrometry-mass spectrometry using methanol and/or acetonitrile for solid-phase desorption and gradient liquid chromatography

Thirty-seven polar pesticides, mainly triazines, phenylurea herbicides and phenoxy acids, were determined by LC-atmospheric pressure chemical ionisation MS-MS with methanol and acetonitrile as the organic modifiers. For most pesticides, detection limits were the same irrespective of the modifier. However, for the phenylurea herbicides, propachlor, carbetamide, triadimefon, triadimenol, triethylcitrate, benzothiazole and metazachlor, the results were much poorer in the presence of acetonitrile; in several cases, no meaningful results were obtained at all. When carrying out trace enrichment of 100 ml water samples on a 10x2 mm I.D. solid-phase extraction precolumn containing a polymeric sorbent, rapid desorption with a small volume of pure organic solvent and the introduction of a T-piece in between the solid-phase extraction precolumn and the analytical column was necessary. Aliquots of 300 microl of acetonitrile were optimal for the complete desorption of all analytes from the sorbent. With methanol as the modifier and when using an identification criterion of three ions, the detection limits for most analytes, in the full-scan mode, were 10-100 ng/l. The linearity of the procedure, which was tested at the 0.1 and 1 microg/l levels, was satisfactory in the positive, but not in the negative ionisation mode. The procedures were used to analyse surface water samples.