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 microg 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).

Formation of gas-phase clusters monitored during electrospray mass spectrometry: a study of quaternary ammonium pesticides.

Gas-phase cluster formation between the quaternary ammonium pesticides paraquat, diquat, difenzoquat, chlormequat and mepiquat, and chloride and acetate anions present in a liquid chromatography (LC) mobile phase, has been studied using electrospray mass spectrometry. The clusters of paraquat, mepiquat and chlormequat were revealed over the entire m/z range of the mass spectrometer, and their formation is dependent on the concentrations of both the cationic and the anionic species. Mepiquat and chlormequat form clusters of the type [2M(q)(+) + A(-)](+), where M(q)(+) is the quaternary ammonium cation and A(-) is the anion. Paraquat forms a cluster species with ammonia and also an ion-pair complex with chloride anions. Diquat and difenzoquat did not form observable ion-pair complexes or clusters with any of the anions studied. Competitive binding of acetate and chloride anions reflects the higher charge density of chloride, which forms the dominant clusters with mepiquat and chlormequat. The formation of cluster species has implications for the quantification of quaternary ammonium pesticides and may have an influence on the linearity of calibrations.

Tandem mass spectrometric analysis of quaternary ammonium pesticides.

A detailed MS(n) study on an ion trap instrument of the quaternary ammonium pesticides paraquat, diquat, difenzoquat, mepiquat and chlormequat reveals a number of ions not reported previously, and has allowed examination of the fragmentation pathways. A number of transitions that are highly specific to each quat have been identified. Optimal ion trap operating conditions determined using Simplex optimisation can promote either detection of a particular fragmentation transition or a range of MS/MS product ions with a high overall signal response. Thus, fragmentation conditions were optimised to enhance the specificity or sensitivity of MS/MS methods.

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.

Determination of residues of pirimicarb and its desmethyl and desmethylformamido metabolites in fruits and vegetables by liquid chromatography-electrospray/mass spectrometry.

A method was developed for the simultaneous determination of residues of pirimicarb (I) and its desmethylformamido (II) and desmethyl (III) metabolites in plums, peas, green beans, broad beans, carrots, and swedes. The compounds were extracted with ethyl acetate and determined, without cleanup, by reversed-phase liquid chromatography and electrospray mass spectrometry (MS). MS and MS/MS were used concurrently to monitor the protonated molecules and their common collision-induced dissociation product. The limit of detection (signal-to-noise ratio of >3) was 1 ng/mL, corresponding to crop concentrations of <0.0015 mg/kg. All 3 compounds were determined in plums, broad beans, and green beans by MS without interference. Interferences which affected the determination of desmethylformamido-pirimicarb in peas, and to a lesser extent in carrots and swedes, were eliminated by MS/ MS. Recoveries for all 3 compounds, at 0.05 mg/kg for plums and 0.005 mg/kg for other commodities, were in the range 83-124%. No interconversion of I, II and III, occurred during extraction, and the compounds were stable in extracts for > or = 7 days under appropriate conditions.

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%).

Determination of pyrrolizidine alkaloids in honey from selected sites by solid phase extraction and HPLC-MS.

A method was developed for the determination in honey of the Ragwort (Senecio jacobaea) derived pyrrolizidine alkaloids jacoline, jacozine, jacobine, seneciphylline and senecionine, combining solid-phase extraction with high performance liquid chromatography and atmospheric pressure chemical ionization mass spectrometric detection. The method allowed determination of individual alkaloids and offered a considerable improvement in terms of speed, sensitivity and specificity over previous approaches, but was not suitable for determination of jaconine, a minor alkaloid in Ragwort. Instrument calibrations were linear over the range 0.005 to 100 micrograms/ml, equivalent to approximately 0.001 to 2.0 mg/kg in honey with the extraction method used and allowing for observed recoveries. Detection limits in honey were 0.002 mg/kg. Recoveries for most of the alkaloids were between 57 and 70%. The alkaloids have been determined in a number of samples of honey selected after pollen identification and counting. The alkaloids were not detectable in samples containing two grains or less of Ragwort pollen per gram of honey. Samples collected in late July and August contained Ragwort pollen at 15-21 grains/g and total alkaloid concentrations of 0.011-0.056 mg/kg. Similar contributions to the total were made by jacozine, seneciophylline and senecionine, with jacobine making a larger and jacoline a smaller contribution. Two samples of honey containing Ragwort pollen at 24 and 16 grains/g had total alkaloid concentrations of 0.42 and 1.48 mg/kg respectively (not corrected for recovery). The alkaloid profile in these samples was dominated by seneciphylline and senecionine which together comprised 90-95% of the total. Alkaloids were not detected in retail honeys.

Determination of the pesticide fenbutatin oxide in tomatoes, cucumbers and bananas by high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometry.

A rapid method, using high-performance liquid chromatography (HPLC)/ atmospheric pressure chemical ionization-mass spectrometry, has been developed for the determination of fenbutatin oxide in tomatoes, cucumbers and bananas. Samples were homogenized with sodium carbonate and ethyl acetate, filtered through sodium sulphate, concentrated and solvent exchanged into acetonitrile prior to analysis. HPLC was performed on a Hypercarb column with 10:90 acetic acid (5% v/v glacial acetic acid in water)/acetonitrile at a flow rate of 1 mL/min. Positive ionization selected-ion monitoring was performed on the 7 isotopic cluster ions from the tris(2-methyl-2-phenylpropyl) tin fragment. A comparison of solvent-based and extract-based standards showed that tomato and cucumber matrices had a slight enhancement effect on the signal intensity, whereas the banana matrix exerted a signal suppression effect. Calibration was linear over the range 0.25-5.0 ng/microL. The mean spike recoveries (extracts spiked at 0.5 mg/kg) were 88% for tomatoes and 80% for both cucumbers and bananas with relative standard deviations of 6%, 7% and 8% respectively. Limits of detection were commodity dependent and ranged from 0.06-0.12 ng/microL (equivalent to 0.01-0.02 mg/kg in the crop). Ionization was stable for long analytical time periods.

Extraction of maleic hydrazide residues from potato crisps and their determination using high-performance liquid chromatography with UV and atmospheric pressure chemical ionisation mass spectrometric detection.

A method was required for the determination of maleic hydrazide residues in potato crisps. A published method for the extraction of the analyte from onions and potatoes was evaluated and found to be inappropriate due to the inability of the extracting solvent to penetrate the oily matrix. A method was developed to overcome this problem; the resulting recovery data (mean = 92.9%, R.S.D. = 8.3%, n = 16) confirmed its efficiency, and was used to analyse 48 retail potato crisp samples. To confirm possible residues identified by screening with HPLC-UV, an HPLC-atmospheric pressure chemical ionization MS method was developed. There was good agreement between the data obtained from the two detection techniques (R2 = 0.978, slope = 1.11).

Analytical methods for the determination of sterigmatocystin in cheese, bread and corn products using HPLC with atmospheric pressure ionization mass spectrometric detection.

Methods have been developed for the determination of sterigmatocystin in bread, maize and cheese using HPLC linked to mass spectrometry (MS) atmospheric pressure chemical ionization for detection and concurrent confirmation of sterigmatocystin at levels down to less than 5 micrograms/kg. Candidate extraction methods were initially checked for recovery and reproducibility by spiking commodities at a level of 200 micrograms/kg of sterigmatocystin and using HPLC with post-column derivatization. Recovery was found to be greater than 90% for bread and maize, and 75% for cheese. Mass spectrometer conditions for detecting sterigmatocystin were established by injecting solutions directly into the mass spectrometer. Extracts of bread, maize grits and cheese prepared by the candidate extraction methods were examined using HPLC/MS using samples spiked at a level of 20 micrograms/kg of sterigmatocystin. Results for bread and maize samples showed that the extraction procedure recovered more than 90% of added sterigmatocystin and produced extracts free of interference from co-extractives, with limits of detection of less than 2 micrograms/kg for both commodities. The HPLC/MS results for cheese extracts gave lower average recoveries of 55%. These results were also more variable. However, the apparent limit of detection for sterigmatocystin in cheese was still about 4 micrograms/kg.

PCDDS and PCDFS in milk from farms in Derbyshire, U.K.

As part of a programme to establish the background levels of PCDD/Fs in milk in the U.K., samples of cows' milk were collected from farms in Derbyshire in 1990 and 1991. The concentrations of PCDD/Fs in the samples from two farms in the Bolsover area of Derbyshire were found to be significantly elevated compared with the normal range for PCDD/Fs in milk in the U.K. Details of the findings and the actions taken as a result are given. The concentrations of PCDD/Fs in milk from those farms previously supplying milk for human consumption are now below the Maximum Tolerable Concentration of 17.5 ng TEQ/kg fat.

Levels of PCDDs, PCDFs and non-ortho PCBs in dietary supplement fish oil obtained in Spain.

Levels of PCDDs, PCDFs and non-ortho PCBs are reported for fish oils available in Spain which are consumed by the population as a dietary supplement. Trace enrichment methodology based on the use of modified silica and activated carbon chromatography was combined with on-column extraction (FMS 100) to separate PCDDs, PCDFs and PCBs from lipid material. The extracts were further cleaned up on disposable Florisil columns and analysed by HRGC/HRMS (PCDD/F and non-ortho PCB fractions). Mean levels found in the samples were 10.50 ppt for total PCDDs and 9.95 ppt for total PCDFs. Calculated PCDD/F I-TEQ values were found to be 2.11 ppt on a lipid weight basis. Total mean levels found for co-planar PCBs (#77, 126 and 169) were 18.26 ppt and the calculated I-TEQ value was 0.31 ppt on a lipid weight basis.

Levels of selected ortho and non-ortho polychlorinated biphenyls in UK retail milk.

Nineteen pooled samples of retail cow's milk were analysed for ortho (PCBs 28, 52, 101, 118, 138, 153 and 180) and non-ortho (PCBs 77, 126 and 169) polychlorinated biphenyls. Concentrations of individual congeners in whole milk were in the ranges 2 to 95 ng/kg for ortho substituted PCBs (51 to 2440 ng/kg fat) and 0.05 to 0.6 ng/kg for non-ortho substituted PCBs (1.3 to 15.4 ng/kg fat). These values provide a preliminary estimate of background contamination levels for polychlorinated biphenyls in UK milk. Results expressed in TEQs, using the recently proposed WHO/IPCS TEFs, averaged 0.06 ng TEQ/kg whole milk.

Contaminants of food : Prioritisation scheme to identify manufactured organic chemicals as potential contaminants of food.

A scheme has been developed to rank 70 industrial organic chemicals in order of their priority for further study as potential contaminants of food. Numerical scales were developed for the following seven key criteria concerning environmental issues, food and toxicity: -Production volume -Pattern of usage -Possible fate in the environment -Likelihood of chemical entering the food chain -Mechanism of entry into the food chain -Persistence and accumulation in the food chain -Toxicity. Each chemical was assigned a score for the above criteria, which were combined to give an overall ranking for the chemicals.This scheme has been endorsed by the MAFF Steering Group on Chemical Aspects of Food Surveillance. It will be used in the assessment of relative priorities for further non-statutory surveillance for these contaminants in the UK food supply.

Determination of the pesticide diflubenzuron in mushrooms by high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry.

A method using high-performance liquid chromatography-atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) has been developed and validated for the determination of the insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] in mushrooms. Samples were homogenised with acetone, extracted into dichloromethane-cyclohexane and further cleaned-up by size-exclusion chromatography (SEC). HPLC was performed on an ODS column with methanol-water at 1 ml/min. The limit of detection was 0.02 ng/microl (equivalent to 0.017 mg/kg in the crop). The calibration was linear over the range 0.025-1.0 ng/microl. Recovery of diflubenzuron from spiked mushrooms (0.06-0.58 mg/kg) was 85.5% with a relative standard deviation of 14.5% (n = 56).

Determination of the pesticides diflubenzuron and clofentezine in plums, strawberries and blackcurrant-based fruit drinks by high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometry.

A high performance liquid chromatographic/atmospheric pressure chemical ionization-mass spectrometric (HPLC/APCI-MS) method has been developed for the determination of the pesticides diflubenzuron (1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea) and clofentezine (3,6-bis(2-chlorophenyl)-1,2,4,5-tetrazine) in plums, strawberries and blackcurrant-based fruit drinks. Samples were homogenized with acetone, extracted into dichloromethane + cyclohexane and cleaned-up by high performance gel permeation chromatography. HPLC was performed on an ODS column with methanol + water at 1 mL/min. Detection was by negative-ion selected-ion monitoring APCI-MS. Comparison of response with solvent and matrix-matched standards showed some enhancement of response for the latter, and these standards were consequently used for quantification. The calibration was linear over the range 0.05-0.50 ng/microL in all three matrices. The mean overall recovery of diflubenzuron and clofentezine from spiked extracts (0.086 mg/kg) in all three matrices was 76% and 70% respectively with relative standard deviations of 15% and 12% respectively (n = 12). The limit of detection was both compound and commodity dependent and ranged from 0.01-0.05 ng/microL, equivalent to 0.003-0.014 mg/kg in the crop.

Analysis of sulphonamides using supercritical fluid chromatography and supercritical fluid chromatography-mass spectrometry.

Packed-column supercritical fluid chromatography has been used for the separation of mixtures of sulphonamides on silica and amino-bonded stationary phases utilizing carbon dioxide with methanol modifier as the mobile phase. The effect of modifier concentration, column pressure and modifier identity on retention was also studied. Packed-column supercritical fluid chromatography-mass spectrometry (SFC-MS) of these mixtures utilizing both moving-belt and modified thermospray interfaces was also studied. The identification of sulphamethazine in a spiked porcine kidney extract was performed by SFC-MS using the moving-belt interface.

Analysis of drug residues in tissue by combined supercritical-fluid extraction-supercritical-fluid chromatography-mass spectrometry-mass spectrometry.

The combination of supercritical-fluid extraction-supercritical-fluid chromatography-tandem mass spectrometry has been evaluated for the detection of residues of a small group of veterinary drugs in freeze-dried pig's kidney. During extraction with supercritical CO2 the drugs were retained by the column while non-polar endogenous material was not retained and thus passed to waste. Subsequent changes to the mobile phase composition eluted the drugs which were detected with high specificity by tandem mass spectrometry. Although the sensitivity in this preliminary study was not adequate for surveillance or enforcement, there is potential for further development of the approach.

Detection of residues of chloramphenicol in crude extracts of fish and milk by tandem mass spectrometry.

The collision-induced dissociation mass spectrum, observed with a hybrid tandem instrument, of the ammonia chemical ionization protonated molecular ion of chloramphenicol was used for the detection of residues of the drug in biological samples. The extracted oil from fish was subjected to a rapid clean-up on a pre-packed silica gel cartridge prior to non-chromatographic tandem mass spectral analysis. Fat extracted from milk was analysed directly by on-line combined high-performance liquid chromatography/tandem mass spectrometry with rapid elution of chloramphenicol. Identification was on the basis of agreement of the daughter ion spectra obtained from sample extracts with that of the chloramphenicol standard. Detection was unambiguous at 0.5 mg kg-1. The sensitivity advantage normally expected with multiple reaction monitoring was not achieved owing to the effect of neutral noise phenomena.