A.C. Hogenboom

Ultra-trace-level determination of polar pesticides and their transformation products in surface and estuarine water samples using column liquid chromatography–electrospray tandem mass spectrometry

A method is developed for the determination of polar pesticides and their transformation products [atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, diuron, 3,4-dichlorophenylmethylurea, 3,4-dichlorophenylurea (DPU), monuron, bentazone, anthranil-isopropylamide, chloridazon, metolachlor] in surface, estuarine and sea water samples at the low ng/l level. Solid-phase extraction is combined off-line with column liquid chromatography-electrospray ionization tandem mass spectrometric detection (LC-ESI-MS-MS). The applicability of two solid-phase materials, i.e., LiChrolut EN cartridges and graphitized carbon black extraction disks, is evaluated. The influence of the organic solvent used in gradient LC, as well as the amount of co-extracted humic material on the ESI process is studied. The eluotropic strength of the organic solvent was found to have a distinct effect on the sensitivity of ESI-MS if coupled with LC gradient separations. Methanol gave much better results than acetonitrile and phenylurea compounds are more susceptible to solvent changes than triazines. Co-extracted humic material causes signal suppression in ESI-MS-MS detection. The degree of suppression depends upon the sample pH and the nature of the samples, i.e., surface or estuarine water. Detection limits in LC-ESI-MS-MS ranged from 0.2 to 2 ng/l, with the exception of DPU (8 ng/l). The applicability of the procedure was demonstrated by analyzing surface and estuarine water.

Analytical strategies for the screening of veterinary drugs and their residues in edible products

The development of analytical strategies for the regulatory control of drug residues in food-producing animals is discussed. Analytical methods for the determination of veterinary drugs in edible products are based on microbiological, immunochemical and physicochemical principles. Because of complexity of biological matrices such as egg, milk and meat, well designed, and often sophisticated, off-line or on-line sample treatment procedures are essential, especially when utilising physicochemical multi-residue screening procedures. Since large series of samples have often to be analysed, automation is increasingly becoming important. Confirmation of the identity of drug residues and validation of the analytical results implies the use of adequate analytical methods. In its turn, this requires well established criteria for those methods and/or equivalent reference methods.

Rapid target analysis of microcontaminants in water by on-line single-short-column liquid chromatography combined with atmospheric pressure chemical ionization tandem mass spectrometry

The applicability of trace enrichment and separation of microcontaminants on a 10 mm x 2 mm I.D. high-pressure packed (8 microns C18 bonded silica or 10-15 microns PLRP-S) column combined on-line with an atmospheric pressure chemical ionization MS-MS system is demonstrated for the target analysis of herbicides in river water. Tailor-made procedures are obtained for a limited number of analytes by tuning the chromatographic efficiency of the short LC column and the specificity of tandem MS, in order to minimize the analysis time. With the on-line short-column LC-MS-MS method, good linearity is obtained for the herbicides in the range of 0.1-10 micrograms/l. The relative standard deviations of peak areas are less than 5% and, with only 4-ml samples, detection limits of 0.01-0.1 microgram/l can be achieved. The total analysis time is 10-15 min. The 10 mm x 2 mm I.D. LC columns packed with 8 microns particles show good stability and can be used for at least 40 analyses. Target compound analyses of river water allowed the confirmation of the presence of herbicides such as diuron, simazine, atrazine and terbutylazine at sub-microgram/l levels.

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).

On-line dual-precolumn-based trace enrichment for the determination of polar and acidic microcontaminants in river water by liquid chromatography with diode-array UV and tandem mass spectrometric detection

Dual-pre-column-based trace enrichment combined on-line with liquid chromatography-diode-array UV and tandem mass spectrometric detection was used to determine a wide polarity range of organic microcontaminants in river water. Various sorbents were studied for their extraction efficiency of (highly) polar and acidic compounds and their ability to selectively remove humic substances, which are normally co-extracted and interfere in the UV detection of polar microcontaminants. An optimised on-line dual-pre-column set-up with PLRP-S in the first pre-column and Hysphere-1 in the second pre-column was used to study the analytical performance of the procedure. Tandem MS was used for confirmation purposes and to quantify the organic microcontaminants in river water at the low-ng/l level. In addition, the influence of the type of sample (drinking and river water) on suppression of analyte responses in electrospray ionization MS was studied.

Determination of pesticides in vegetables using large-volume injection column liquid chromatography–electrospray tandem mass spectrometry

Direct injection of a large volume (900 microl) of a sample extract onto a liquid chromatographic (LC) column, LC separation and electrospray tandem mass spectrometric detection were used for the quantitative analysis of a wide polarity range of pesticides in carrots and potatoes. Rapid sample preparation involved extraction of a small amount of sample (2 g) with a small volume of organic solvent (3 ml), clean-up over a filter and dilution of the organic extract with the aqueous LC eluent. The extraction efficiency for the selected pesticides was studied using methanol, acetone and acetonitrile as solvents. Evaluation of the performance of the overall method, using extraction with acetonitrile and detection in the selected-reaction-monitoring mode, showed excellent linearity in the range of 2-100 microg/kg with limits of detection of 0.5-2 microg/kg for both types of vegetable. With relative standard deviations of the MS peak area measurements of less than 6.5% (n=8) the repeatability of the method was fully satisfactory.

Accurate mass determinations for the confirmation and identification of organic microcontaminants in surface water using on-line solid-phase extraction liquid chromatography electrospray orthogonal-acceleration time-of-flight mass spectrometry.

The identification of polar microcontaminants in surface water is an important issue in environmental analysis. Liquid chromatography/mass spectrometry (LC/MS) is frequently applied for this purpose. However, even in combination with tandem mass spectrometry (MS/MS), unambiguous identification of the compounds detected is often difficult. The potential of an alternative strategy, based on the ability of an orthogonal-acceleration time-of-flight mass spectrometer to routinely perform accurate mass determination at 10 ppm in on-line LC/MS, is explored. On-line solid-phase extraction LC electrospray orthogonal-acceleration time-of-flight mass spectrometry is shown to enable the determination of pesticides from various compound classes in surface water in the concentration range of 0.1 to 10 micrograms/L. In addition, the ability to discriminate and unambiguously identify pesticides in mixtures of isobaric and/or isomeric compounds is investigated.

Effect of the mobile phase composition on the separation and detection of intact proteins by reversed-phase liquid chromatography-electrospray mass spectrometry.

Various buffers (ammonium acetate, ammonium formate, and ammonium hydrogencarbonate), acids (formic acid, acetic acid, heptafluorobutyric acid, and trifluoroacetic acid), and bases (ammonium hydroxide and morpholine) covering the range from 2 to 11.5 have been investigated for their performance in the separation of proteins by reversed-phase liquid chromatography (RPLC) and in their detection by electrospray mass spectrometry (ESI-MS). These additives were first tested for the detection of standard proteins by ESI-MS by flow-injection analysis (FIA). Those additives yielding the highest signals were employed for the separation of standard proteins by using three different reversed-phase columns: two C18 columns (4.6 mm I.D. and 2.1 mm I.D.) and one perfusion column (2 mm I.D.). The sensitivity of the LC-MS system was evaluated with the column giving the best results and with those LC eluents enabling the LC separation of the proteins and also yielding the highest MS signals. For that purpose, calibration curves were compared for both LC-MS and FIA-MS. Formic acid was the additive yielding the highest responses in FIA-MS and trifluoroacetic acid (TFA) gave the best separation and recovery of the proteins. However, problems related to poor recovery of the proteins in the column when formic acid was used and the significant signal suppression observed in MS when TFA was employed, made neither of them suitable for the sensitive detection of the proteins in LC-MS.

On-line solid-phase extraction-short-column liquid chromatography combined with various tandem mass spectrometric scanning strategies for the rapid study of transformation of pesticides in surface water.

The applicability of solid-phase extraction-short-column liquid chromatography using two short columns (i.e., 10 and 20 mm long) coupled on-line with tandem mass spectrometric detection is demonstrated for the rapid degradation study of pesticides and their transformation products in water at the low-microgram/l level. Photolysis was used as a means to transform the parent compounds into their degradation products and the experiments were carried out at environmentally relevant concentrations. The use of on-line sample enrichment/separation in photodegradation studies allows the rapid analysis of aqueous samples directly after irradiation without further transformation of the compounds of interest. The versatility of MS allows various selective screening strategies to be employed, i.e., full-scan mode, neutral loss, precursor-ion and product-ion scan modes. This allows the identification of possible degradation products and the calculation of the rates of disappearance of the parent compound and appearance of transformation products.

The role of column liquid chromatography–mass spectrometry in environmental trace-level analysis. Determination and identification of pesticides in water

Keywords: Review; Liquid chromatography; Tandem mass spectrometry; Microcontaminants; Environmental trace-level water analysis