R.B. Geerdink

Rapid Screening of a Large Group of Polar Pesticides in River Water by On-Line Trace Enrichment and Column Liquid Chromatography

Abstract Column liquid chromatography on a reversed-phase (C-18) analytical column using a linear acetonitrile-water gradient and diode-array detection is used in an on-line early-warning system of over 50 pesticides in surface water. It allows the separation of most compounds with detection limits of about 1–5 μg/1 after preconcentration of 30 ml of sample. Problems encountered for co-eluting pesticides with similar spectra and pesticides with weak ultraviolet absorption over 230 nm, are discussed. If the system is combined with on-line trace enrichment on a styrene-divinylbenzene copolymer (PLRP-S) precolumn, the overall resolution is only slightly affected, and the qualitative information obtained remains about the same. Chromatograms of spiked (2–10 μg/1) surface (river Rhine) water containing 54 test compounds are shown. Preliminary studies show the stability of several pesticides in water to be rather low. Some degradation products have been detected in 1-month-old methanolic and aqueous solutions.

Fully automated on-line liquid chromatographic separation system for polar pollutants in various types of water

A fully automated column liquid chromatographic separation system using on-line trace enrichment, gradient elution and diode-array detection for the trace-level determination of polar pollutants is described. Automation of the system was achieved by means of an automated cartridge-exchange system (PROSPEKT). Relevant parameters such as pH, volume and ionic strength of the sample, flow-rate during the enrichment step and wavelengths and band widths during detection were optimized for eighteen pollutants in various types of water at concentration levels below 5 μg l−1. The determination limit for all test compounds in liquid chromatographic grade water was 0.1 μg l−1, and identification, via diode-array spectra, could be performed at the same level. The mean relative standard deviations of the peak areas and the retention times for all the test compounds were 10% and 0.3%, respectively, at the 5 μg l−1 level for river Rhine water.

Trace-level determination of pesticides in water by means of liquid and gas chromatography

The trace-level determination of pesticides and their transformation products (TPs) in water by means of liquid and gas chromatography (LC and GC) is reviewed. Special attention is given to the use of (tandem) mass spectrometry for identification and confirmation purposes. The complementarity of LC- and GC-based techniques and the potential of comprehensive GCXGC are discussed, and also the impressive performance of time-of-flight mass spectrometry. It is also indicated that, in the near future, the TPs rather than the parent compounds should receive most attention--with a better understanding of matrix effects and eluent composition on the ionization efficiency of analytes being urgently required. Finally, the merits of using much shorter LC columns, or even no column at all (flow-injection analysis) in target analysis are shown, and a more cost-efficient and sophisticated strategy for monitoring programmes is briefly introduced.

Determination of polar pollutants in water using an on-line liquid chromatographic preconcentration system

SummaryAn isocratic column liquid chromatographic system with UV absorbance detection at 230 nm has been developed for the rapid trace-level determination of a large number of polar pollutants in water. The systems contains two precolumns, in series, which are packed with a styrenedivinylbenzene (PLRP-S) polymer. The second precolumn is also loaded with sodium dodecylsulphate before use. Each precolumn is combined with a PLRP-S analytical column, and aqueous acetonitrile mixtures (pH 3) are used for the separation of neutral as well as acidic and basic pollutants. With 10-ml water samples the detection limits for all analytes, in tap water, are in the low to sub μg/l range. Relevant analytical data are reported and the advantage of using a dodecylsulphate-loaded precolumn over a cation-exchange precolumn is discussed.

Comparison between positive, negative and chloride-enhanced negative chemical ionization of organophosphorus pesticides in on-line liquid chromatography—mass spectrometry

Positive and negative chemical ionization (PCI and NCI, respectively) have been used for the characterization of ten organophosphorus pesticides in on-line liquid chromatography-mass spectrometry (LC-MS). LC analyses were performed on a 20 cm X 0.7 mm I.D. C8-bonded phase using acetonitrile-water (70:30) or acetonitrile-water-chloroacetonitrile (69:30:1) as eluent. With PCI, molecular weight information was obtained with both eluents. For NCI considerable differences in the spectra were found using the two eluents. Without chloroacetonitrile the spectra were dominated by the functional group fragment and with chloroacetonitrile the base peak was [M - R]- with R being methyl or ethyl, while the spectra further contained the functional group ions. Special emphasis was devoted to the occurrence of chloride attachment at different source temperatures. With several compounds the [M + Cl]- ion was formed and its relative intensity strongly increased when the source temperature decreased. With NCI the sensitivity was about one order of magnitude better than with PCI. This advantage was partly lost when 1% of chloroacetonitrile was used in the eluent; on the other hand, complementary structural information was obtained. As an application, the determination of three organophosphorus pesticides in sediment is reported.

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 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.

Determination of phenoxyacid herbicides in water : Polymeric pre-column preconcentration and tetrabutyl-ammonium ion-pair separation on a PRP-1 column

Optimum conditions for preconcentration of phenoxyacid herbicides from water on polymeric material and separation on an analytical column (PLRP-S) and PRP-1 respectively) have been achieved. The method consists of (a) an on-line preconcentration at pH 3, (b) clean-up with four (precolumn) bed volumes of acetonitrile-water (30:70) at pH 3 and (c) isocratic analytical separation at pH 11 with 0.01 mol/l tetrabutylammonium as the ion-pair reagent and acetonitrile-water (30:70) as the eluent. Data on the repeatability of the method, sample flow dependence and sorption capacity are reported. For reliable integration of the chromatogram a clean-up step was introduced. This washing procedure however is more effective for tap-water than for surface water samples. The results of the method are promising and indicate that 10-50 ml of surface water can be applied to the precolumn without breakthrough. Detection limits in surface water samples are 0.1-0.5 micrograms/l whereas those in tap water are 10-50 ng/l. The applicability fo the method was tested. The results of this method were in good agreement with gas chromatographic-mass spectrometric results, and only ca. 0.1 microgram/l lower over the entire range, whereas the analysis time was much shorter. The potential of this technique for automation was demonstrated using a microprocessor-controlled column-switching unit, resulting in a reduction of the total analysis time to ca. 20 min.

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.

On-line trace enrichment for improved sensitivity in liquid chromatography with direct liquid introduction mass spectrometric detection

Abstract Two model systems consisting of (1) phenylurea herbicides and (2) nitro aromatics were chosen to demonstrate the potential of on-line trace enrichment. The liquid chromatography—mass spectrometry system consists of a 2-MM-I.D. precolumn and analytical column combined with a direct liquid-inlet interface with a helium jet principle. The mass spectrometer has been operated in the positive and negative chemical-ionisation modes. For the investigated compounds, on-line trace enrichment can give enrichment factors of two to three orders of magnitude. For dinitroaromatics detection limits of 0.01 parts per billion were obtained, which corresponds to absolute detection limits of 1 pg. Band broadening was of the order of 1 sec (σ t ).