J. Slobodnik

Column liquid chromatography-mass spectrometry: Selected techniques in environmental applications for polar pesticides and related compounds

Abstract A review covering the field of environmental applications of liquid chromatography-mass spectrometry (LC-MS) is presented. Recent developments and advances are discussed with emphasis on the presently popular thermospray, particle beam and atmospheric pressure ionisation interfaces. Each interface is described separately covering the principle of operation, typical detection limits and characteristics of the mass spectra. All reviewed interfacing techniques provide useful data for identification/confirmation of analytes with various chemical properties. The application-oriented part of the review primarily deals with polar pesticides and related compounds. However, generally speaking the conclusions which are drawn also hold true for other classes of micro-contaminants. LC-MS obviously is complementary to ‘routine’ GC-MS and it extends the boundaries of the ‘analytical window’ of mass spectrometry to polar, non-volatile and/or thermolabile compounds. LC-MS is a powerful tool in environmental analysis and especially when it is combined with appropriate sample-treatment procedures it allows one to obtain detection limits adequate for trace-level analysis.

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.

Trace-level determination of pesticide residues using on-line solid-phase extraction-column liquid chromatography with atmospheric pressure ionization mass spectrometric and tandem mass spectrometric detection

Abstract Column liquid chromatography (LC) with pneumatically assisted electrospray (PA-ESP) or atmospheric pressure chemical ionization (APCI) followed by (tandem) mass spectrometry (MS or MS-MS) was used for the analysis of a test mixture of 17 pesticides. In order to achieve low-ng/l detection limits, solid-phase extraction (SPE) of a 100-ml aqueous sample on a small cartridge packed with a hydrophobic sorbent was used. The LC set-up was coupled on-line to the MS part of the system. The complete analysis was automated by means of a gradient controller and a Prospekt valve switching, solvent selection and cartridge exchange unit. When using SPE-LC with either APCI or PA-ESP, the detection limits of 15 (out of the 17) pesticides in tap water were 0.007–3 μg/l in the full-scan and 0.1–200 ng/l in the SIM mode, with an analysis time of 65 min. Fenchlorphos and bromophos-ethyl could not be detected by either ionization method. APCI full-scan spectra showed much less sodium and acetonitrile/water cluster adducts than PA-ESP spectra. Negative ion (NI) operation was less sensitive for the majority of the compounds tested (73 in total), but several organophosphorus pesticides, nitrophenols and chlorophenols only gave a response in the NI mode. PA-ESP-MS-MS and APCI-MS-MS gave similar product-ion spectra from protonated molecules; an MS-MS library was built for more than 60 pesticides and their degradation products, at constant settings of collision gas pressure (argon, 2.0 × 10−3 Torr) and collision energy (25 eV). The library was successfully used for searching product-ion spectra from SPE-LC-APCI-MS-MS at low levels (10 ng/l) in tap water and for the identification of atrazine in surface water (estimated concentration 0.25 μg/l).

Solid-phase extraction of polar pesticides from environmental water samples on graphitized carbon and Empore-activated carbon disks and on-line coupling to octadecyl-bonded silica analytical columns.

The suitability of Empore-activated carbon disks (EACD), Envi-Carb graphitized carbon black (GCB) and CPP-50 graphitized carbon for the trace enrichment of polar pesticides from water samples was studied by means of off-line and on-line solid-phase extraction (SPE). In the off-line procedure, 0.5-2 l samples spiked with a test mixture of oxamyl, methomyl and aldicarb sulfoxide were enriched on EnviCarb SPE cartridges or 47 mm diameter EACD and eluted with dichloromethane-methanol. After evaporation, a sample was injected onto a C18-bonded silica column and analysed by liquid chromatography with ultraviolet (LC-UV) detection. EACD performed better than EnviCarb cartridges in terms of breakthrough volumes (> 2 l for all test analytes), reproducibility (R.S.D. of recoveries, 4-8%, n = 3) and sampling speed (100 ml/min); detection limits in drinking water were 0.05-0.16 microgram/l. In the on-line experiments, 4.6 mm diameter pieces cut from original EACD and stacked onto each other in a 9 mm long precolumn, and EnviCarb and CPP-50 packed in 10 x 2.0 mm I.D. precolumn, were tested, and 50-200 ml spiked water samples were preconcentrated. Because of the peak broadening caused by the strong sorption of the analytes on carbon, the carbon-packed precolumns were eluted by a separate stream of 0.1 ml/min acetonitrile which was mixed with the gradient LC eluent in front of the C18 analytical column. The final on-line procedure was also applied for the less polar propoxur, carbaryl and methiocarb. EnviCarb could not be used due to its poor pressure resistance. CPP-50 provided less peak broadening than EACD: peak widths were 0.1-0.3 min and R.S.D. of peak heights 4-14% (n = 3). In terms of analyte trapping efficiency on-line SPE-LC-UV with a CPP-50 precolumn also showed better performance than when Bondesil C18/OH or polymeric PLRP-S was used, but chromatographic resolution was similar. With the CPP-50-based system, detection limits of the test compounds were 0.05-1 microgram/l in surface water.

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.

Trace-level detection and identification of polar pesticides in surface water : the SAMOS approach

Abstract In recent years, much attention has been devoted to the low- and sub-μg/l trace-level determination of polar pesticides and related chemical compounds in surface and drinking water. The large number of analyses that have to be carried out and the general demand for speed and automation require the development of on-line and integrated analytical systems. Recent developments in the area of on-line trace enrichment-LC or GC separation—detection/identification SAMOS systems are discussed. The practicality of the approach is highlighted by giving real-life examples taken from studies on the quality of the surface water of several European rivers.

Liquid chromatography — Particle beam mass spectrometry for identification of unknown pollutants in water

SummaryTrace enrichment on a precolumn packed with copolymer material, coupled on-line with reversed-phase, column liquid chromatography-particle beammass spectrometry (RPLC-PB-MS) has been used for both target and non-target analysis of water samples. RPLC is carried out on a C-18-bonded silica column using a linear acetonitrile-0.1 M ammonium acetate gradient. Using optimised PB-MS conditions and 100–250 ml water samples, the detection limits for several phenylureas are in the 0.03–0.05 μg l−1 range using the full-scan mode; repeatability is good and the LC-PB-MS system is robust. Several surface and drinking water samples have been analysed and low levels of various environmental contaminants have been identified using electron impact mass spectra. Applying chemical ionisation with methane as reagent gas in both the positive and negative mode in conjunction with PB-MS provides relevant confirmatory information.

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.

Single short-column liquid chromatography with atmospheric pressure chemical ionization - (tandem) mass spectrometric detection for trace environmental analysis.

SummarySingle short, i.e. ca 2-cm long, high-pressure-packed columns coupled with mass spectrometric (MS) or tandem MS detection enable rapid trace-level determination and identification of environmental pollutants in water samples. In this study an atmospheric pressure chemical ionization (APCI) interface has been used and the overall set-up was tested with a mixture of seventeen pesticides, including organophosphates, carbamates, phenylureas and triazines. For the majority of the test analytes, the most prominent peaks in the positive-ion APCI-MS spectra resulted from protonated molecules. For fifteen out of the seventeen pesticides short-column liquid chromatography (LC)-APCI-MS of water samples as small as 15 mL resulted in detection limits between 0.03 and 5 μg L−1 in full-scan mode and between 2 and 750 ng L−1 by selected ion monitoring (SIM), both recorded in the positive-ion mode. Production spectra from protonated molecules of the majority of the selected pesticides present at a level of 0.1 μg L−1 in tap water are successfully identified from a search against a pesticide MS-MS library compiled in-house. This short-column LC-APCI-MS(-MS) approach has, on the basis of full-scan positive-ion data and their product-ion spectra, also been used to confirm the identity of target compounds and to identify unknown organic micropollutants in environmental waters.