Francisco Javier Arrebola

Pesticide trace analysis using solid-phase extraction and gas chromatography with electron-capture and tandem mass spectrometric detection in water samples

Gas chromatography (GC) with electron-capture detection (ECD), mass spectrometry (MS) and tandem mass spectrometry (MS-MS) were employed for the identification of 12 pesticides in water samples. For this purpose, a solid-phase extraction procedure with C18 cartridges was used, optimising the breakthrough volume and the saturation concentration. In GC-MS-MS, the lowest detectable concentrations for the pesticides were between 2 and 26 ng l(-1), recoveries ranged from 70 to 133% in water samples spiked at 100 ng l(-1) and the relative standard deviations were in the range 5.3 to 17.4%. The proposed analytical methodology was applied to analyse pesticides in wetland samples from Almería (Spain).

Application of gas chromatography–tandem mass spectrometry to the analysis of pesticides in fruits and vegetables

A new analytical method was devised using gas chromatography with tandem mass spectrometry (GC-MS-MS) for the routine analysis of 31 multi-class pesticide residues and approximately 8000 fresh fruit and vegetable samples (green bean, cucumber, pepper, tomato, eggplant, watermelon, melon, and marrow). Extraction of the pesticides with dichloromethane was carried out. The optimal ionization mode, either electron impact or chemical ionization, was selected for each pesticide in the same run. Carbofrit was used in the liner and combined with the selectivity of the detector this avoided additional clean-up. Thus, not only was money and time saved, the uncertainty of the method was decreased in its application to routine analysis. The average recoveries in cucumber obtained for each pesticide ranged between 71 and 119% at two different fortification levels (n=10 each) that ranged between 7 and 300 ng g(-1) (depending on the pesticide). The relative standard deviation was lower than 19% for all compounds tested. The calculated limits of detection and quantification were typically <1 ng g(-1) which were much lower than the maximum residue levels established by European legislations.

Determination of endosulfan and its metabolites in human urine using gas chromatography–tandem mass spectrometry

A method was developed for determining the occupational exposure to endosulfan and its main metabolites (endosulfanether, -lactone and -sulfate) in human urine using dieldrin as an internal standard. Solid phase extraction (SPE) and gas chromatography-tandem mass spectrometry (GC-MS-MS) have been used due to their high sensitivity and selectivity in avoiding most matrix interferences. The recovery efficiencies of the tested compounds yielded more than 89.2% at the fortification level of 10 ng ml(-1) in urine and their relative standard deviations were between 9.1 and 12.8%. The detection limit of each compound ranged between 6 and 18 pg ml(-1). Urine samples from nine pest control operators were analysed and total endosulfan concentrations between 94 and 2038 pg ml(-1) were found.

Multifamily determination of pesticide residues in soya-based nutraceutical products by GC/MS–MS

An analytical method based on a modified QuEChERS extraction coupled with gas chromatography-tandem mass spectrometry (GC-MS/MS) was evaluated for the determination of 177 pesticides in soya-based nutraceutical products. The QuEChERS method was optimised and different extraction solvents and clean-up approaches were tested, obtaining the most efficient conditions with a mixture of sorbents (PSA, C18, GBC and Zr-Sep(+)). Recoveries were evaluated at 10, 50 and 100 μg/kg and ranged between 70% and 120%. Precision was expressed as relative standard deviation (RSD), and it was evaluated for more than 160 pesticides as intra and inter-day precision, with values always below 20% and 25%, respectively. Limits of detection (LODs) ranged from 0.1 to 10 μg/kg, whereas limits of quantification (LOQs) from 0.5 to 20 μg/kg. The applicability of the method was proved by analysing soya-based nutraceuticals. Two pesticides were found in these samples, malathion and pyriproxyfen, at 11.1 and 1.5 μg/kg respectively.

Excretion study of endosulfan in urine of a pest control operator

A study of endosulfan excretion in human urine was carried out by using an agricultural worker involved with spraying, wearing protective overall, gloves and breathing mask. The urine samples were extracted with Solid Phase Extraction (SPE) cartridges and the compounds were separated and detected using Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS) due to their high sensitivity and selectivity in preventing most matrix interferences. The alpha- and beta-isomers of endosulfan were detected (total concentrations ranged between 5368 and 2239 pg/ml) but endosulfan-ether, -lactone or -sulphate were not found above the detection limits. The results obtained were compared with the concentrations found for a non-occupational exposed man. Statistical interpretation of the excretion-rate of the insecticide was performed by assuming that it can be described as a first-order kinetic. The constant rate and the half-lives were determined.

Monitoring of 6-chloronicotinic acid in human urine by gas chromatography-tandem mass spectrometry as indicator of exposure to the pesticide imidacloprid

A new analytical method for determining 6-chloronicotinic acid (6-ClNA) in human urine is proposed. 6-ClNA is the main metabolite in warm-blooded animals after exposure to the insecticide imidachloprid. 6-ClNA was extracted from human urine using solid phase extraction (SPE) with laboratory-made cartridges of Amberlite XAD-4. A clean-up step and a derivatization process were carried out prior to gas chromatography-tandem mass spectrometric (GC-MS-MS) determination. A study on the influence of pH in the extraction process revealed that it affects the analyte extraction efficiency. A working pH zone was defined between 0.8 and 2.8. Calibration curves were studied in the concentration range of 0.5-100 ng mL(-1) and showed good linearity. Limits of detection and determination of the method were 16 and 56 pg mL(-1) respectively. The mean recovery at 10 and 100 ng mL(-1) was between 97.2 and 102.1% and the repeatability was lower than 5.4% in all cases. The analysis of urine samples of five agricultural workers from Almería (Spain) did not detect the metabolite.

Comparison of gas chromatography with NPD, MS, and tandem MS-MS in the multiresidue analysis of pesticides in environmental waters

SummaryGas chromatography (GC) with nitrogen-phosphorus detection (NPD) and mass spectrometry (MS), in full scan and tandem (MS-MS) modes have been used to determine eleven pesticides in aqueous samples. Preconcentration of 500 mL water with C18 cartridges enabled the determination of pesticides at ng L−1 levels. The best precision and sensitivity were obtained from GC-NPD and GC-MS-MS. The limits of detection were between 4 and 44 ng L−1 for NPD and 1 and 40 ng L−1 for MS-MS. The application of this methodology to the determination of pesticides in real samples was tested by analyzing wetland samples from province of Almería (Spain). The results obtained were compared and the advantage of MS-MS over NPD for highly selective quantitative determination of pesticides in complex matrices is discussed.

Determination of parts per trillion levels of benzoylurea pesticides in groundwater by high-performance liquid chromatography-electrospray ionization mass spectrometry

SummaryA high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ES-MS) method has been developed for the determination of five benzoylurea pesticides, diflubenzuron, flufenoxuron, hexaflumuron, lufenuron, and triflumuron, in groundwater samples. Initially two atmospheric-pressure ionization techniques, electrospray (ES) and atmospheric pressure chemical ionization (APCI), both in positive- and negative-ion modes, were compared. Performance data for the method, e. g. recovery, sensitivity, precision, and linearity, show the reliability of the method for analysis of water samples. The lowest detectable concentrations of the pesticides were between 0.3 and 6.0 ng L−1 and recoveries were from 95 to 104% for water samples spiked at 10 ng L−1; relative standard deviations were in the range 5–15%. The HPLC-ES-MS method was applied to the determination of the five compounds in groundwater samples.

Multi-Residue Method For Determination of Pesticides in Vegetable Samples by GC-MS-MS

SummaryA method for detection, quantification, and confirmation of 30 multi-class pesticide residues in fresh vegetables by gas chromatography-tandem mass spectrometry (GC-MS-MS) has been developed. The optimum ionization mode, electron impact (El-MS-MS) or chemical ionization (Cl-MS-MS), was used for different groups of pesticides in a single run. The residues were previously extracted from vegetables with dichloromethane. A 10μL aliquot of the extract can be injected in routine analysis without a clean up step when the glass liner is used with Carbofrit. Recovery efficiencies ranged 70–119% at the two different fortification levels studied and the relative standard deviation was <16.9% for all compounds. The limit of detection of each compound was 30 ng Kg−1−6 μg Kg−1. The proposed method was applied to the routine analysis of pesticides in vegetables grown in an important greenhouses area located in El Ejido (Almería, Spain).

Development and Validation of a Multiresidue Method for the Determination of Pesticides in Dry Samples (Rice and Wheat Flour) Using Liquid Chromatography/Triple Quadrupole Tandem Mass Spectrometry.

A rapid and sensitive multiresidue method was developed and validated for the determination of around 100 pesticides in dry samples (rice and wheat flour) by ultra-performance LC coupled to a triple quadrupole mass analyzer working in tandem mode (UPLC/QqQ-MS/MS). The sample preparation step was optimized for both matrixes. Pesticides were extracted from rice samples using aqueous ethyl acetate, while aqueous acetonitrile extraction [modified QuEChERS (quick, easy, cheap, effective, rugged, and safe) method] was used for wheat flour matrixes. In both cases the extracts were then cleaned up by dispersive solid phase extraction with MgSO4 and primary secondary amine+C18 sorbents. A further cleanup step with Florisil was necessary to remove fat in wheat flour. The method was validated at two concentration levels (3.6 and 40 μg/kg for most compounds), obtaining recoveries ranging from 70 to 120%, intraday and interday precision values≤20% expressed as RSDs, and expanded uncertainty values≤50%. The LOQ values ranged between 3.6 and 20 μg/kg, although it was set at 3.6 μg/kg for the majority of the pesticides. The method was applied to the analysis of 20 real samples, and no pesticides were detected.