P. van Zoonen

Microwave assisted solvent extraction (MASE) for the efficient determination of triazines in soil samples with aged residues

SummaryThe use of microwave-assisted solvent extraction (MASE) as an alternative for conventional solvent extraction procedures for the determination of some triazine herbicides in soil samples has been investigated. In this study MASE method development was focused on the selection of a suitable extraction solvent prior to the instrumental analysis of uncleaned extracts with gas chromatography and nitrogen-specific detection. A mixture of dichloromethane-methanol (90∶10, v/v) yielded recoveries ranging from 89 to 103 (spiked level 200 μg/kg) with RSDs ranging from 2.1 to 5.3%. This solvent mixture is also very convenient for further procedure. The selected MASE procedure was tested by analyzing freshly spiked soil samples and samples with aged residues of atrazine, desethylatrazine, desisopropylatrazine and simazine. The results were compared with those obtained by a conventional liquid extraction method. The comparative study indicated that MASE yields recoveries at least as good as those obtained by the conventional method. Moreover, the MASE procedure provides low solvent consumption in combination with a high sample throughput.

Automated solid-phase extraction coupled to gas chromatography with electron-capture detection: a combination of extraction and clean-up of pyrethroids in the analysis of surface water.

The combination of automated solid-phase extraction (SPE) and large-volume introduction gas chromatography electron-capture detection (GC-ECD) is used for the determination of synthetic pyrethroids in surface and drinking water. The selectivity that is needed for the use of GC-ECD of environmental samples is achieved by addition of a polarity modifier to the sample. In this study, sufficient methanol was added to 19 ml of sample to obtain a level of 30% of modifier prior to SPE. The cartridge is washed with one additional ml of 30% methanol in water. After drying, the cartridge is eluted with toluene. GC-ECD analysis is performed by on-column introduction of 100 microliters of the toluene extract. The whole procedure was automated by using an automated solid-phase extraction apparatus. Limits of detection (LODs) for the pyrethroids in surface water are in the range of 1 to 8 ng/1 (signal-to-noise ratio = 3); even lower limits of detection are possible for drinking water.

Column-switching RPLC for the trace-level determination of ethylenethiourea in aqueous samples

SummaryColumn-switching with two C18 separation columns combined with UV detection at 233 nm has been used to determine ETU in ground water samples. The direct assay of ETU (limit of detection, 1 ppb) takes less than 10 min. For the determination of ETU down to a level of 0.1 ppb, preconcentration of ETU is achieved by a liquid-liquid extraction procedure allowing the analysis of at least 12 water samples per day.For both methods (1-ppb and 0.1-ppb level), the overall recovery (96 and 82%), the repeatability (4.5 and 4.3%) and the reproducibility (5.0 and 7.9%) are satisfactory (n=18 and 28, respectively). More than one hundred samples of ground water were analysed during a 10-month period; over 0.1 ppb of ETU (range, 0.1–300 ppb) was found in 30% of the samples tested.

Applicability of coupled-column liquid chromatography to the analysis of β-agonists in urine by direct sample injection I. Development of a single-residue reversed-phase liquid chromatography-UV method for clenbuterol and selection of chromatographic conditions suitable for multi-residue analysis

Abstract Optimisation procedures originally applied to coupled-column RPLC-UV for the residue analysis of polar pesticides were evaluated for the analysis of β-agonists in human and bovine urine using direct sample injection. Two approaches have been studied: (i) a multi-residue method (MRM) for the clean-up and separation of eight different β-agonists (isoprenaline, cimaterol, terbutaline, salbutamol, fenoterol, ractopamine, clenbuterol and mabuterol) and (ii) a single-residue method (SRM) focussed at the detection of clenbuterol residues in samples of urine. Both approaches provided efficient procedures to process urine samples automatically with coupled-column LC. Particular attention was paid to selecting analytical conditions suitable for thermospray MS detection, which is to be investigated in the near future. Though UV detection cannot offer enough selectivity for the simultaneous screening of a group of β-agonists, coupled-column RPLC-UV proved to be very powerful in SRM, allowing the detection of clenbuterol at the μg/1 level in filtered (0.45 μm) human and bovine urine after direct sample injection.

Determination of organochlorine compounds in fatty matrices application of rapid off-line normal-phase liquid chromatographic clean-up

A clean-up method for organochlorine compounds in fatty samples based on normal-phase liquid chromatography (NPLC) is described. To this end, an existing clean-up procedure which uses column switching for the separation of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) from the fat matrix was simplified to a single silica LC column procedure. The use of an LC column packed with 3 microns silica enables complete fat/OCP separation in a total fraction volume of 12 ml, and results in a fully automated clean-up procedure that takes only 32 min per sample. The method showed average recoveries of 80-110% in the concentration range of 1-510 micrograms/kg, with relative standard deviations of less than 10%. Limits of determination were in the range of 0.5-50 micrograms/kg. The simplified approach has shown its potential for a variety of samples, such as milk, pork fat, animal feed and cod liver oil, showing its general applicability to fatty samples.

Coupled column liquid chromatography for the trace determination of polar pesticides in water using direct large-volume injection: method development strategy applied to methyl isothiocyanate

The potential of coupled column liquid gas chromatography (LC) for the trace determination of a single polar compound by direct large-volume injection of aqueous samples was studied and a general approach to method development for this class of compound is discussed. As a new application, the determination of methyl isothiocyanate (MITC) by means of reversed-phase (RP) LC column switching and UV detection at 237 nm is reported. With direct injection of 770-μl samples, the detection limit is 1 μg l−1 and the time of analysis is about 10 min. For a further increase in selectivity and detectability (down to a level of about 0.1 gmg l−1), a rapid liquid-liquid extraction followed by an organic-aqueous phase switch on a silica cartridge is required prior to RPLC. No residues of MITC were found in over 200 surface water samples investigated.

Coupled-column reversed-phase liquid chromatography in environmental analysis

Abstract An overview is given of the applicability of coupled-column reversed-phase liquid chromatography (LC-LC) to the trace analysis of organic micropollutants in environmental samples, based on typical examples of recent and current work. Although LC-LC, as applied to the analysis of polar pesticides in environmental samples, is usually based on the use of two separation columns with almost similar stationary phase selectivity, it will be shown that a considerable gain in the overall selectivity of methods is attainable. Moreover LC-LC provides sensitivity and potential for automation by utilisation of large volume injections. Due to the large number of parameters involved in the development of analytical procedures a systematic approach towards methodology is discussed. Two basic types of applications are treated: (i) single-residue methodology focused at the rapid determination of one analyte and (ii) multi-residue methodology for the simultaneous determination of a number of analytes.

Coupled-column reversed-phase liquid chromatography—UV analyser for the determination of polar pesticides in water

Abstract Coupled-column RPLC with UV detection using direct large volume injections of up to 4 ml can be used for the rapid and sensitive determination of single polar pesticides in environmental water samples. The limits of determination for pesticides such as bentazone and isoproturon are 0.1 μg/l in real-life samples and the sample throughput is 5–7/h. Linearity is observed over at least three decades and the repeatability is satisfactory (relative standard deviations 3–7% at spiking levels of 0.1–0.5 μg/l). The set-up is fully automated and shows good robustness. The coupled-column RPLC-UV analyser has successfully been used in several monitoring programmes.

Screening and analysis of polar pesticides in environmental monitoring programmes by coupled-column liquid chromatography and gas chromatography—mass spectrometry

Screening and analysis of polar pesticides based on coupled-column reversed-phase liquid chromatography (LC-LC) and GC- or LC-MS is a powerful tool in the execution of environmental monitoring programmes. This paper presents a unified approach utilising LC-LC screening followed by GC-MS confirmation. As polar pesticides are not generally amenable to GC a widely applicable derivation technique is used. The results demonstrate that the proposed LC and MS techniques are capable of analysing a wide range of polar pesticides down to levels of 0.1 microgram/l (EU limit for drinking water). LC switching techniques for group analysis or individual compounds rely on the reversed-phase retention and the UV detectability of the pesticides in combination with the choice of the LC columns. Fast miniaturised derivatization prior to GC-MS forms an integral part in the proposed strategy. In order to avoid extraction losses, derivation in the aqueous sample, preferably with electrophoric reagents with enhanced sensitivity in GC-NICI-MS are employed where possible. In this communication, method development and validation fitting in the strategy are evaluated and the results of the combined approach are discussed.

Rapid method for the determination of eight chlorophenoxy acid residues in environmental water samples using off-line solid-phase extraction and on-line selective precolumn switching

A rapid procedure for the determination of eight chlorophenoxy acid herbicides in environmental water samples is described. The method involves two off-line solid-phase extraction (SPE) procedures prior to analysis by liquid chromatography with (pre)column switching and UV detection at 228 nm. SPE sample pretreatment consists in loading a 50-ml sample on a 100-mg C18 cartridge followed by clean-up of the extract on a 100-mg silica cartridge. The extracts obtained by this procedure are analysed with coupled column liquid chromatography (LC) using a precolumn packed with internal surface reversed-phase material (5-μm GFF II) and an analytical column packed with C18 material (3-μm Microspher). The separation of the extracts from the SPE procedure takes less than 15 min, rendering an overall procedure with a throughout of 40 samples per day. The chlorophenoxy acids 2,4-D, MCPA, 2,4-DP, MCPP, 2,4,5-T, 2,4-DB, MCPB and 2,4,5-TP can be assayed in the various water samples down to a level of 0.1 μg l−1. Drinking, ground and surface water samples spiked at levels of 0.5 and 2.0 μg l−1 yielded average recoveries between 80 and 110% (n=5 for each sample type and spiked level)_with relative standard deviations between 1 and 10%. The calibration graphs are linear over at least three orders of magnitude.