E. R. Brouwer

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.

Determination of polycyclic aromatic hydrocarbons in surface water by column liquid chromatography with fluorescence detection, using on-line micelle-mediated sample preparation

Abstract Column liquid chromatography with fluorescence and diode-array UV detection has been used for the trace-level determination of sixteen EPA-priority polycyclic aromatic hydrocarbons. The procedure involves on-line micellemediated preconcentration on selective sorbents. Using Brij-35 as the surfactant, unwanted adsorption of the analytes on inner walls or surfaces is prevented. The system has been used for the analysis of surface water samples, and detection limits typically are at the low- to sub-ng/l level. The system is robust and repeatability is excellent.

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.

Fully automated multi-residue method for trace level monitoring of polar pesticides by liquid chromatography

Abstract A fully automated liquid chromatographic method using on-line trace enrichment, gradient elution and diode-array detection for the trace level determination of polar pesticides in surface water is described. The automated system uses specially developed software in the form of “user macros”, allowing the on-line control of both the automated cartridge exchange unit for sample preparation and the liquid chromatograph with diode-array detector by means of the Pascal Workstation computer of that liquid chromatographic system. The collected data are automatedly evaluated, i.e., pollutants present in the sample at a concentration level above an input treshold level are identified/determined and a report is printed. Parameters such as the sampling interval of the spectra, temperature of the analytical column compartment, wavelength/bandwidth ratios and data handling were optimized. The validation results for 27 pesticides are presented. At an analyte concentration of 1 μg/1 the relative standard deviations of the retention times and peak areas in different types of water are in the range 0.2–1.5% and 1–15%, respectively. All calibration graphs are linear in the range 0.1–7 μg/1.

Use of membrane extraction disks for on-line trace enrichment of organic compounds from aqueous samples

SummaryMembrane extraction disks have been recently introduced for the solid-phase extraction of organic compounds from aqueous samples. The material consists of alkyl-modified silica particles enmeshed in an inert PTEE matrix. Aqueous samples containing polar pesticides and herbicides, are preconcentrated on-line from acidic solutions on membrane extraction disks containing immobilized octadecyl-modified silica and analyzed with an isocratic liquid chromatographic system using PLRP-S as the stationary phase and aqueous acetonitrile mixtures (pH 3) as the eluent. Data on the lifetime and the dimensions of the preconcentration disks, and the efficiency and the repeatability of the procedure are reported. For 10 ml samples, the detection limits of the analytes atrazine, simazine and 2,3,4-trichlorophenol in tap water are 0.1–1 ppb.

Determination of phenolic compounds in surface water using on-line liquid chromatographic precolumn-based column-switching techniques

Abstract Gradient LC-diode array UV detection, combined on-line with a PLRP-S and an ENVI-Chrom P precolumn in series, enables the on-line trace-level determination and provisional identification of phenol and 13 substituted phenols in surface water. Additional selectivity has been incorporated into the system by properly utilizing the breakthrough properties of phenol over the PLPP-S precolumn. With 50-ml sample volumes, the limits of detection for all analytes are at the low- to sub-μg/1 level.

On-line low-level screening of polar pesticides in drinking and surface waters by liquid chromatography—thermospray mass spectrometry

Abstract Mass spectra of 39 carbamate, triazine, phenylurea and organophosphorus polar pesticides were obtained by liquid chromatography—mass spectrometry with a thermospray interface. The analytes generated [M + H]+ or [M + NH4]+ as the base peak with methanol−0.1 M ammonium acetate as the mobile phase in the discharge positive-ion mode. Chlorophenols showed much better sensitivity in the negative-ion mode; their spectra were dominated by the deprotonated molecular ion. Trace enrichment of these pesticides on a 10 mm × 3.0 mm I.D. precolumn packed with C18-bonded silica was coupled on-line with reversed-phase column liquid chromatography—thermospray mass spectrometry (LC-TSP-MS). The LC separation was carried out on a 250 × 4.6 mm I.D. C18-bonded silica column using a linear methanol—aqueous ammonium acetate gradient [10:90 to 90:10 (v/v) in 45 min]. When optimized TSP-MS conditions and 50-ml water samples were used, the detection limits for the pollutants tested typically were in the 2–90 ng/l range with time-scheduled selected-ion monitoring; the repeatability was good and the LC-TSP-MS system was robust. Several surface and drinking water samples were analysed and low levels of simazine, atrazine, isoproturon and diuron were detected.

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.

Selected procedures for the monitoring of polar pesticides and related microcontaminants in aquatic samples

There is an increasing need to monitor trace-level concentrations of organic micropollutants in water, especially in surface and tap water. In the present review, attention is mainly devoted to the determination of polar pesticides. After an introduction which briefly explains the reasons to select this group of analytes, the advantages of on-line monitoring procedures for early-warning and rapid-screening purposes are outlined. The main part of the paper is devoted to a discussion of selected papers from the recent literature, which combine sample treatment by means of solid-phase extraction (SPE), and a liquid (LC) or gas (GC) chromatographic separation-cum-detection procedure in one set-up. Aspects of special interest include (i) the variety of detectors in use with both SPE-LC and SPE-GC procedures, (ii) the increasing popularity of (on-line and off-line) SPE-LC-MS techniques, and (iii) the high potential of SPE-GC as well as alternative sample treatment-GC procedures.

Liquid chromatographic determination of polar pollutants in surface water using membrane extraction disks for on-line trace enrichment

Abstract Membrane extraction disks loaded with alkyl-bonded silica, copolymer or ion-exchange material have been tested for the on-line trace enrichment of polar pesticides from surface water. To this end, a new membrane extraction disk holder has been designed, which can be used in the forward flush and backflush mode. The basic compounds carbendazim, chloridazon, simazine and 4-chloroaniline were used as test compounds. They are preconcentrated from acidic solution using one or two membrane extraction disk holders in series (operated in the reversed-phase and ion-pair mode), and analysed by gradient liquid chromatography with polymer PLRP-S as the stationary phase and aqueous acetonitrile mixtures (pH 3) as the eluent. Data on the efficiency and repeatability of the on-line procedure are reported. Preconcentration of 30 ml of surface (river Rhine) water allows the UV detection of the four pollutants at the 0.1 μg 1−1 level.