A. De Kok

Low ng/1-level determination of twenty N-methylcarbamate pesticides and twelve of their polar metabolites in surface water via off-line solid-phase extraction and high-performance liquid chromatography with post-column reaction and fluorescence detection

Abstract Reversed-phase high-performance liquid chromatography (HPLC) was used for the determination of twenty parent N-methylcarbamate pesticides and twelve major metabolites in surface water. A 50-ml water sample was passed through a disposable solid-phase extraction cartridge, packed with 500 mg of low-carbon C 18 -bonded silica (C 18 /OH, 40 μm particle size), which selectively retained polar compounds. The preconcentrated analytes were eluted with acetonitrile, reconstituted in 1 ml of water and 100 μl were injected into the HPLC system. The carbamates were separated via a water-methanol-acetonitrile gradient. Detection was performed via postcolumn hydrolysis on a solid-phase (anion-exchange) catalyst, derivatization of the methylamine formed with o -phthalaldehyde-2-mercaptoethanol and fluorescence detection of the isoindole derivative. The detection limits for surface water were between 20 and 30 ng/l. Recoveries were determined for thirteen carbamates and ten metabolites at the 0.1 and 1 μg/1 level and generally ranged from 76 to 106% with relative standard deviations (R.S.D.s) of 0.5–8.5%. Only the sulphoxide metabolite of ethiofencarb and thiofanox had lower recoveries and correspondingly higher R.S.D.s.

Chromatographic determination of phenylurea herbicides and their corresponding aniline degradation products in environmental samples. I.

Abstract Several chromatographic procedures for the determination of fifteen phenylurea herbicides and their corresponding degradation products are reported. Methods of analysis for each separate class of compounds and multiresidue methods which allow selective determination of herbicides and anilines in each others presence are discussed. The various procedures involve steps such as extraction, clean-up, catalytic hydrolysis of herbicides to anilines, liquid or gas chromatographic fractionation and/or separation, chemical derivatization and detection.

Determination of phenylurea herbicides via direct derivatisation with heptafluorobutyric anhydride

Abstract Direct derivatisation of fifteen phenylurea herbicides with heptafluorobutyric anhydride (HFBA) has been studied. Quantitative conversion is obtained within 1 h at 60°C, using hexane as solvent. The nuclear magnetic resonance and mass spectrometric characteristics of the HFB-herbicides are reported, as well as their behaviour in adsorption high-performance liquid chromatography and capillary gas chromatography; detection limits are of the order of 50 pg and 1 pg, respectively, using electron-capture detection. Applications to water and crop samples are reported.

Gas chromatographic analysis of phenylurea herbicides following catalytic hydrolysis on silica gel

SummaryA method is described for the rapid catalytic hydrolysis of phenylurea herbicides on silica gel at elevated temperatures. After derivatisation of the anilines produced with heptafluorobutyric acid anhydride final analysis is done on a gas chromatograph equipped with an electroncapture detector. Detection limits are in the 1–5 picogram range. The method has successfully been applied to residue analysis of water samples at the 1 ppb level. The determination of free anilines present in water samples and the potential of various techniques to be used to discriminate between free anilines and parent herbicides are also discussed.

Analysis of polybrominated biphenyls

High-performance liquid chromatography, gas chromatography-mass spectrometry, ultraviolet spectrometry and nuclear magnetic resonance spectrometry have been used to characterize the behaviour of a number of individual brominated biphenyls and to assess the composition of several mixtures of these compounds. The dependence of retention and spectral characteristics on the bromine content of the substituted biphenyls is discussed and the behaviour of polybrominated biphenyls is compared with that of polychlorinated biphenyls. The applicability of high-performance liquid chromatography to photodegradation studies is demonstrated.

Analysis of polychlorinated naphthalenes by high-performance liquid and thin-layer chromatography

Abstract High-performance liquid chromatography (HPLC) in the system silica gel-dry n-hexane has been used to characterize the behaviour of several series of commercially available mixtures of chlorinated naphthalenes, viz., Halowax 1031–1051, Clonacire 90–130 and Nibren D88–D130. A large number of peaks in the chromatograms of the Halowaxes have been assigned to individual constituents. To this end, retention times and UV spectra have been recorded for 33 polychlorinated naphthalenes. The dependence of retention and spectral characteristics on the number and position of the chlorine atoms in the naphthalene nucleus is discussed. The results of HPLC are compared with those obtained with several normal and reversed-phase thin-layer chromatographic systems.

High-speed liquid and thin-layer chromatography of polychlorinated biphenyls

High-speed liquid chromatography in the system silica gel/dry n-hexane and ultraviolet spectrometry have been used to study the composition of various types of commercially available mixtures of chlorinated biphenyls. Special attention has been paid to the analysis of highly chlorinated products. In addition to data previously published, retention times are recorded for 11 individual polychlorinated biphenyls. The results of high-speed liquid chromatography are compared with those obtained in several normal and reversed-phase thin-layer chromatographic systems.

Improved interface for liquid chromatography—electron-capture detector coupling. I

Abstract An improved design of an interface for the coupling of a liquid chromatograph and an electron-capture detector (ECD) is described and the dependence of extra-column band broadening on the dimensions of the capillary tube in this interface is studied. Use of the improved design enables the detection of high-boiling compounds which could not be handled with a previously available commercial interface. For several high-boiling halogenated bi- and terphenyls, and organochlorine pesticides, ECD detection limits (which often are in the low-picogram range) have been determined and compared with UV detection limits. The ECD calibration curves are linear over 3 orders of magnitude. The optimized liquid chromatography—ECD system is applied to environmental analysis in the system silica—dry hexane. Finally, it is demonstrated that the addition of up to at least 6% of dioxane to the hexane used as mobile phase can be tolerated without unacceptable loss of performance.

The use of various chromatographic techniques for the determination of phenylurea herbicides and their corresponding anilines in environmental samples. II: Applications

In earlier work, various strategies have been developed for the trace-level determination of phenylurea herbicides and the anilines which are their main degradation products. They include catalytic hydrolysis of the phenylureas on silica, liquid chromatographic fractionation of complex mixtures of herbicides and anilines, derivatization of anilines and herbicides with electron-capture-sensitive reagents, and final analysis by means of capillary gas chromatography. In the present paper, the application of these principles to trace-level analysis of surface water, soil and crop samples is demonstrated.

An Evaluation of Chromatographic Methods for the Analysis of Polychlorinated Terphenyls in Environmental Samples

Gas chromatography (GC) with packed and capillary columns, high-performance liquid chromatography (HPLC) and thin-layer chromatography have been used to characterize various commercially available mixtures of polychlorinated terphenyls (PCTs). Besides, UV absorption and mass spectrometry data have been collected, and the behaviour of PCTs upon perchlorination to the tetradecachloroterphenyls has been studied. Using GC, the PCT content of a number of paper and sewage sludge samples has been determined. The application of perchlorination/GC as method of analysis often yields unreliable, i.e., too high, results compared with the direct GC pattern-comparison method. In the case of paper samples, hydrogenated terphenyls appear to be the principal interfering compounds.