James R. Startin

Analysis of glyphosate and glufosinate by capillary electrophoresis-mass spectrometry utilising a sheathless microelectrospray interface

The potential of capillary electrophoresis combined with mass spectrometry for the simultaneous determination of two herbicides (glyphosate and glufosinate) and their metabolites (aminomethylphosphonic acid and methylphosphinicopropionic acid) as the native species is demonstrated utilising a simple microelectrospray interface. The interface uses the voltage applied to the CE capillary to drive separation and generate the electrospray, avoiding sample dilution associated with the use of a sheath liquid interface. The chemistry of the internal walls of the capillary has a marked influence on peak shape, and appropriate choice is essential to successful operation of the interface. A linear polyacrylamide coated capillary, which has no electroosmotic flow, gave best reproducibility, with precision of migration time and peak area in the range 1-2 and 7-12% RSD, respectively, for the four analytes. Limits of detection, low-pg on-column, are substantially better than for previous methods and calibration curves over the range 1-100 microM have R2 values greater than 0.97. The observed concentration limit of detection for glyphosate in water is 1 microM and for a water-acetone extract of wheat is 2.5 microM, allowing the underivatised herbicide to be detected at 10% of the maximum residue limit in wheat.

Concentration changes for 5 PCDD/F congeners after administration in beef cattle.

Ten cattle were treated with daily doses of five PCDD/F congeners, over a 4 week period. Four control animals were not treated. They were subsequently slaughtered as three groups, at 5, 18 and 31 weeks after the first dose. All congeners showed an increase in concentration within animal tissues when sampled at 5 weeks post-dosing. Concentrations had reduced after 18 weeks and there was a further small reduction after 31 weeks. Halflives for each congener were calculated at 13-21 weeks (93-148 days). Concentrations of congeners were different in the various tissues analysed. At 5 weeks after dosing commenced, concentrations in sub-cutaneous fat and in perirenal fat were close to 40 ng/kg (a predicted level based on 50% absorption of the dosed compounds). Concentrations on a fat basis in muscle tissue and liver were, however, about 5 and 10 times higher, respectively. The concentrations found in muscle tissue and liver samples taken at 18 and 31 weeks were approximately twice that found in fat deposits, thus the differences were still apparent, but at a reduced level. It is possible that the distribution phase was incomplete and that PCDD/Fs remained predominantly in association with circulating blood lipids rather than in equilibrium with depot fat. It follows that if livestock were recently exposed to PCDD/Fs (for example, through the consumption of contaminated feed), the analysis of depot fats would not necessarily provide a reliable indicator of the concentrations of PCDD/Fs in edible tissues.

Optimisation of ion trap parameters for the quantification of chlormequat by liquid chromatography/mass spectrometry and the application in the analysis of pear extracts.

Optimisation of the activation parameters for ion trap mass spectrometric analysis of the chlormequat cation using simplex optimisation enabled the product ion (m/z 58) response to be improved 1000-fold. A comparison of the sensitivity of the optimised ion trap mass spectrometer with that of a triple quadrupole mass spectrometer for liquid chromatography/tandem mass spectrometry (LC/MS/MS) showed that similar limits of detection (LODs) could be achieved. For the MS/MS transition of the (35)Cl precursor to the most abundant product, LODs were 0.8 ng cation mL(-1) (0.004 mg cation kg(-1) pear equivalent) and 1.0 ng cation mL(-1) (0.005 mg cation kg(-1) pear equivalent) on the triple quadrupole and ion trap instrument, respectively.

Determination of residues of the plant growth regulator chlormequat in pears by ion-exchange high performance liquid chromatography-electrospray mass spectrometry†

We report a method which we have used routinely for the determination of chlormequat residues in pears. After extraction with methanol, determination was performed, without clean-up, by ion-exchange HPLC using an SCX column eluted with aqueous ammonium formate-methanol, and HPLC-MS with an electrospray interface. MS and MS-MS were employed concurrently, using selected ion monitoring and selected reaction monitoring, respectively, of the 35Cl and 37Cl isotopes of the chlormequat cation and the CID transitions of each of these precursors to the common product ion at m/z 58. The method was suitable for determinations at concentrations of chlormequat cation of 0.04 mg kg-1. Concentrations determined using the four signals were in good agreement (mean RSD 3%). The mean recovery of chlormequat cation at 0.16 mg kg-1, measured using the m/z 122-->58 signal, was 86% (RSD 7%) under repeatability conditions and 88% (RSD 15%) in routine application of the method over a 3 month period. Analysis of an in-house reference sample of pears, similarly analysed over the 3 month period, gave an RSD of 10% with a mean of 0.14 mg kg-1. Mean recovery at 0.016 mg kg-1, under repeatability conditions on two occasions, was 101% (RSD 6%) and 56% (RSD 12%).

Isotachophoretic separation of glyphosate, glufosinate, AMPA and MPP with contactless conductivity detection

The potential of isotachophoresis with conductivity detection for the preconcentration, separation and simultaneous determination of two herbicides (glyphosate and glufosinate) and their metabolites (aminomethylphosphonic acid and methylphosphinicopropionc acid) was investigated. A 0.025 μg mL−1 standard solution of all four analytes was easily detectable in a 40 minute analysis using a volume coupled arrangement of two capillaries connected in series. The conductivity relative step heights (RSHs) were used to assign individual analytes in mixtures. Calibrations were carried out over a dynamic range of three orders of magnitude in concentration, with relative standard deviation in zone length (used to quantify the analytes) shown to be in the range 2–6% at 2.5 μg mL−1 loading.

Improved sensitivity in detection of chlormequat by liquid chromatography–mass spectrometry

Two published separations, using electrospray mass spectrometry (ES-MS), exhibit significant differences in limits of detection (LODs) for chlormequat cation in pear. Separation on ODS1, confirmed to result from ion-exchange, gives shorter analysis times and calibration over a wider concentration range than on an SCX cation-exchange column. The superior LOD using ODS1 (0.04 ng ml(-1) vs. 1.0 ng ml(-1)) results mainly from better chromatographic peak shape. Separation on ODS1 combined with optimised ES-MS detection allows direct quantification of chlormequat on an ion trap instrument at levels lower than those required for residue analysis in foods and also in drinking water.

Changes in concentration of five PCDD/F congeners after cooking beef from treated cattle.

A large piece of meat taken from a single animal, which had been dosed with five selected PCDD/Fs, was prepared and cooked by a selection of different methods; burgers (fried, grilled, barbecued), roasts (cooked using conventional and microwave ovens) and stews (open pan and pressure cooked). For some of the cooking methods, concentration changes, on a whole product basis, were observed between raw and cooked product. However, in all cases these could be explained simply through changes arising from loss of water and elimination of PCDD/Fs with released fat. The total amounts of PCDD/Fs present in the system (including in released fat) remained unchanged. Dietary intake of PCDD/Fs could therefore be reduced by the removal of visible fat from meat before cooking and by discarding any fat released from foods during the cooking process.

Determination of residues of propamocarb in wine by liquid chromatography-electrospray mass spectrometry with direct injection

A simple, sensitive and reliable liquid chromatography-mass spectrometry method with direct injection of diluted samples is reported for the determination of propamocarb residues in wine. Red and white wines were diluted 40- and 20-fold, respectively, using water. Liquid chromatography was performed with a mobile-phase gradient and detection was by electrospray mass spectrometry in a positive ionization mode. Propamocarb was detected as the protonated molecular species at m/z 189. Using matrix-matched calibrant solutions, a calibrated range equivalent to 0.05–2.0 mg kg−1 in red and white wines and limits of detection of 0.025 mg kg−1 for white wine and of 0.05 mg kg−1 for red wine (0.00125 μg ml−1 of sample solution injected) were readily achievable. Recovery of propamocarb hydrochloride from wine spiked before dilution was in the range 91–115%. The chromatograms were free of isobaric interferences. In a small wine survey (72 samples), no residues of propamocarb were detected above 0.1 mg kg−1.