A.J.H. Louter

Analysis of microcontaminants in aqueous samples by fully automated on-line solid-phase extraction-gas chromatography-mass selective detection

Abstract The trace-level analysis of unknown organic pollutants in water requires the use of fast and sensitive methods which also provide structural information. In the present study, an on-line technique was used which combines sample preparation by means of solid-phase extraction (SPE) on a small precolumn packed with a hydrophobic phase, and capillary gas chromatography (GC) with mass spectrometric (MS) detection. Sample preparation was carried out in a fully automated SPE module which was connected to the GC system via an on-column interface. The on-column interface was selected because of its wide application range. The mass spectrometer was preferably used in the full-scan acquisition mode because of the intended identification. The total system including the SPE module, was controlled by the MS software which allowed unattended analysis of a series of samples. The feasibility of on-line SPE-GC-MS was demonstrated by analysing a variety of surface water samples in order to detect and identify non-target compounds. With a sample volume of only 10 ml various micropollutants could be identified, and also quantified, at levels below 0.1 μg/l. The system proved to be flexible, and the sample preparation could easily be adapted to analyse organochlorine pesticides by adding 30 vol.% of methanol to the raw sample. Samples were taken from several European (Axios, Greece; Ebro, Spain; Meuse, Netherlands; Nitra, Slovakia; Rhine, Germany; Thames, UK; Varta, Poland) and American (Sacramento, USA; Amazon, Brazil) rivers. An example of the identification of unknown microcontaminants in waste water is also presented, which is further evidence of the robustness and flexibility of the SPE-GC-MS analyzer.

On-line trace-level enrichment gas chromatography of triazine herbicides, organophosphorus pesticides, and organosulfur compounds from drinking and surface waters

A simple, selective and precise procedure for the analysis of water samples by on-line solid phase extraction gas chromatography (SPE-GC) is presented. The determination of several triazines, organophosphorus pesticides, sulfur containing compounds in tap water was performed by SPE-GC using polymer-packed precolumns and flame ionization (FID), nitrogen-phosphorus (NPD) or flame photometric (FPD) detection. A cartridge packed with silica was inserted between the precolumn and the gas chromatograph in order to eliminate trace amounts of water present in the ethyl acetate used as desorption solvent. Incorporation of a drying step allowed the retention gap to be used for the analysis of ca. 100 samples without significant deterioration of the chromatographic peaks. Analyte recovery was at least 72% when 10 ml of tap-water sample were analysed. The detection limits for all analytes in tap water were lower than 0.1 microgram l-1, with all detectors used. Although with NPD and FPD, selectivity and sensitivity were markedly better. The SPE-GC-NPD system has also been used for the analysis of surface-water samples from different European rivers.

Integrated system for on-line gas and liquid chromatography with a single mass spectrometric detector for the automated analysis of environmental samples

Abstract An integrated system has been developed which combines liquid (LC) and gas (GC) chromatographic separation with a single mass spectrometer (MS). On-line solid-phase extraction (SPE) of 10–200 ml aqueous samples on a short (10 × 2.0 mm I.D.) precolumn packed with a styrene-divinylbenzene copolymer is used for analyte enrichment. The trace-enrichment procedure was automated by means of a PROSPEKT cartridge-exchange/solvent-selection/valve-switching unit. After sample loading, the precolumn is eluted on-line in two subsequent runs, first onto the GC-MS system and, next, onto the LC-MS system using a particle beam (PB) interface. Prior to entering the PB-MS, the LC eluent passes through the flow cell of a UV diode-array detector (DAD). Both GC-MS and LC-PB-MS generate classical electron ionisation (EI) and chemical ionisation (CI) spectra which are useful for the identification of low- and sub-μg/l concentrations of environmental pollutants covering a wide polarity and volatility range. The LC-DAD data provide additional means for quantitation and yield complementary spectral information. All three detection systems (GC-MS, LC-DAD, LC-PB-MS) and the trace-enrichment procedure are fully automated and controlled from the keyboard of the central computer. With such a ‘MULTIANALYSIS’ system GC-MS, LC-DAD and LC-MS data of the same sample can be obtained within 3 h. The system was optimised with nine chlorinated pesticides in drinking water as test mixture. With 100-ml samples detection limits in GC-MS were 0.0005−0.03 μg/l, and in LC-PB-MS 0.5–7 μg/l, both in the full-scan (EI) mode. Negative chemical ionisation (NCI) with methane as reagent gas improved the sensitivity of six halogenated compounds 3- to 30-fold and provided relevant information for structural elucidation of unknown compounds in real-world samples. LC-DAD detection limits varied from 0.01 to 0.05 μg/l. Relative standard deviations (R.S.D.) of retention times were less than 0.2% in all systems, R.S.D.s of peak areas were 5–15% for GC-MS and LC-PB-MS and less than 5% for LC-DAD. The ‘MULTIANALYSIS’ system was used to analyse surface water samples and river sediment extracts; several pollutants were detected and identified.

Large-volume injections in gas chromatography-atomic emission detection : an approach for trace-level detection in water analysis

Abstract The ruggedness and analytical performance of on-line capillary gas chromatography-atomic emission detection (GC-AED) have been studied using 100-μl injections of sample solutions in ethyl acetate, via a loop-type interface. A series of organophosphorus compounds were selected as test analytes; they were monitored using the carbon, sulphur, nitrogen, chlorine, bromine and phosphorus channels. The system showed no flame-outs or other maintenance problems even after 300 large-volume injections. The analytical potential of the system, expressed in terms of repeatability, linearity and minimum detectable amount, was not affected and a 100-fold increase in analyte detectability, in terms of concentration units, compared with a conventional 1-μl injection was observed. As an application, GC-AED was combined off-line with solid-phase extraction. Several environmental contaminants were preconcentrated from river and tap water samples, and 20% (100 μl) of the ethyl acetate eluent were directly analysed. With a sample volume of only 10 ml, the detection limits of the organophosphorus pesticides typically were ca. 0.1 μg/l.

Automated on-line solid-phase extraction-gas chromatography with nitrogen-phosphorus detection: determination of benzodiazepines in human plasma.

An automated sample preparation module, the ASPEC (automated sample preparation with extraction columns) was interfaced with a capillary gas chromatograph (GC) by means of a loop-type interface. The system was optimized for the determination of four benzodiazepines in plasma. Extraction from the untreated plasma was carried out on disposable C18 cartridges and involved several washing steps. The analytes were desorbed with 2 ml of ethyl acetate and a 110-microliter aliquot of the eluate was injected into the gas chromatograph via the loop-type interface using fully concurrent solvent evaporation conditions. Detection of the benzodiazepines was carried out with a nitrogen-phosphorus detector (NPD). The ASPEC-GC-NPD was fully automated and could run unattended overnight. With a sample volume of 1 ml the procedure showed good linearity and repeatability in the range 5-50 ng/ml using a sample volume of 1 ml. The limits of detection in plasma were 0.5-2 ng/ml.

Rapid Identification of Benzothiazole in River Water With On-Line Solid-Phase Extraction-Gas Chromatography-Mass Selective Detection

Abstract Solid-phase extraction coupled on-line with gas chromatography-mass spectometry and off-line with gas chromatography-atomic emission detection is shown to be a rapid technique for the trace-level determination and provisional identification of (an) organic pollutant(s) in surface water.

Use of a Drying Cartridge in On-Line Solid-Phase Extraction–Gas Chromatography–Mass Spectrometry

A drying cartridge was used and optimized for the in-line elimination of water from the desorption eluent in on-line solid phase extraction-gas chromatography (SPE-GC). The cartridge is essentially a small stainless- steel precolumn packed with a drying agent which can be regenerated by simultaneous heating and purging with a moisture-free gas. The drying cartridge was mourned on an additional valve instead of between the SPE-GC transfer valve and the on-column injector to enable regeneration of the cartridge during the GC run and, thus, to increase sample throughput. Three drying agents were tested, viz. sodium sulfate, silica and molecular sieves. Although molecular sieves have the highest capacity, silica was preferred because of practical considerations. Large-volume injections were performed through the in-line drying cartridge using a mixture of 23 microcontaminants ranging widely in polarity and volatility. Four solvents were tested. With pentane and hexane, the more polar analytes were retained by the drying cartridge. Ethyl acetate and methyl acetate gave much better (and closely similar) recoveries all analytes. Because water elimination on the silica cartridge proved to be less critical than with ethyl acetate, this solvent was finally selected. The entire SPE-drying cartridge-GC setup was combined with mass spectrometric (MS) detection for the determination of a mixture of micropollutants in real-life water samples. With 10-ml tap water samples spiked at the 0.5 μg/l level, for the majority of the test compounds thee analyte recoveries generally were 60-106%, and (full-scan) detection limits typically were 0.01-0.03 μg/l. Some very polar analytes such as, e.g. dimethoate, were (partially) sorbed onto the silica packing of the drying cartridge.

Use of Chemical Ionization in Multianalysis Gas and Liquid Chromatography Combined With a Single Mass Spectrometer for the Ultra-trace Level Determination of Microcontaminants in Aqueous Samples†

An automated system that comprises a single mass spectrometer (MS) in combination with gas (GC) and liquid chromatography [LC; particle beam (PB) interface] has been used for the trace-level detection and identification of contaminants in water samples. The analytes were enriched by on-line solid-phase extraction (SPE). In the present study, the potential of negative chemical ionization (NCI) detection in this so-called multianalysis system was explored. Attention was devoted to the enhancement of selectivity and sensitivity as well as to the additional spectral information obtained for the identification of unknown compounds.Nine chlorinated pesticides representing three major groups, i.e., triazines, anilides and organophosphorus pesticides, were used as test compounds. Among the three reagent gases used for NCI, isobutane, methane and ammonia, methane gave the best results. For six of the nine pesticides, a 3- to 30-fold increase in sensitivity was observed in the NCI mode as compared with the electron impact (EI) mode. As expected, the NCI mass spectra showed little fragmentation. Electron capture appears to be the dominant ionization mechanism.In order to study the potential of the total on-line SPE–LC/GC–MS set-up, the pesticides were spiked to tap and surface water samples. The detection limits obtained in the NCI (full-scan) mode ranged from 0.1–3 ng l–1 for GC–MS and 50 to 200 ng l–1 for LC–PB–MS for 100-ml tap water samples. The potential of NCI–MS was demonstrated by the identification of several unknown microcontaminants in a river water sample.

Capillary GC with Selective Detection Using on-line Solid Phase Extraction and Liquid Chromatography Techniques

Recent developments in coupling sample preparation and isolation techniques on-line to capillary gas chromatography are outlined. These developments are applied in order to enhance speed and convenience in pesticide trace analysis of tap, ground and surface water. Advantages and disadvantages of the several combination types are discussed and examples for their application in water analysis are shown. Most attention is devoted to the on-line combination of solid-phase extractions and GC using selective detection. The potential and limitations of other combinations, viz. liquid-liquid extraction-GC, solid-phase extraction-thermal desorption-GC open tubular trap-GC and solid-phase micro extraction-GC. Further technical progress may be expected in the area of on-line and automated analyte isolation combined with GC.