Validation and uncertainty study of a comprehensive list of 160 pesticide residues in multi-class vegetables by liquid chromatography–tandem mass spectrometry

Advantages of the scheduled selected reaction monitoring algorithm in liquid chromatography/electrospray ionization tandem mass spectrometry multi-residue analysis of 242 pesticides: a comparative approach with classical selected reaction monitoring mode

This paper illustrates the advantages of using the scheduled selected reaction monitoring (sSRM) algorithm available in Analyst Software 1.5 to build SRM acquisition methods in the application field of pesticide multi-residue analysis. The principle is to monitor the SRM transitions only when necessary. Based on the analytes' retention times, the scheduled SRM algorithm decreases the number of concurrent SRM transitions monitored at any point in time, allowing both cycle time and dwell time to remain optimal at higher levels of SRM multiplexing. To compare the scheduled SRM and the classical SRM modes, a mixture containing 242 multi-class pesticides has been analyzed ten times by three acquisition methods, using liquid chromatography/tandem mass spectrometry (LC/MS/MS) with an API 4000 QTrap mass spectrometer. The scheduled SRM mode demonstrates better results in all fields: more data points per peak, better reproducibility (coefficients of variation (CVs) <5%) and higher signal-to-noise ratio (S/N), even when the number of SRM transitions is doubled. The use of scheduled SRM mode instead of the classical one gives an enhancement of the limits of quantification by a factor two or even higher (up to six), depending on the analyte transitions.

Method development and validation for determination of thiosultap sodium, thiocyclam, and nereistoxin in pepper matrix

This work reports a method for extraction and analysis of thiosultap sodium, thiocyclam, and nereistoxin in pepper. Different extraction methods were tested to attain the best recoveries. The final extraction method combines acetonitrile extraction in an acidic medium with ultrasonic extraction followed by a cleanup step with anhydrous MgSO(4). The analyses were performed on a Linear Ion Trap Quadrupole LC-MS/MS in negative mode for thiosultap sodium and in positive mode for thiocyclam and nereistoxin. Recovery studies carried out on peppers spiked at different fortification levels (20 and 200 μg∙kg(-1)) yielded average recoveries in the range 58-87% with RSD (%) values below 20%. Calibration curves covering two orders of magnitude were performed and they were linear over the concentration range studied (0.001-0.5 mg∙l(-1)). Instrumental detection limits were in the low μg∙kg(-1) range. Stability studies of thiosultap sodium in water were performed by evaluating a 100-μg∙l(-1) solution of this compound in water. It was analyzed over 7 days, after which more than 80% degradation of thiosultap sodium could be observed.

High throughput analysis of 150 pesticides in fruits and vegetables using QuEChERS and low-pressure gas chromatography-time-of-flight mass spectrometry

A higher monitoring rate is highly desirable in the labs, but this goal is typically limited by sample throughput. In this study, we sought to assess the real-world applicability of fast, low-pressure GC-time-of-flight MS (LP-GC/TOFMS) for the identification and quantification of 150 pesticides in tomato, strawberry, potato, orange, and lettuce samples. Buffered and unbuffered versions of QuEChERS (which stands for "quick, easy, cheap, effective, rugged, and safe") using dispersive solid-phase extraction (d-SPE) and disposable pipette extraction (DPX) for clean-up were compared for sample preparation. For clean-up of all sample types, a combination of 150 mg MgSO₄, 50mg primary secondary amine (PSA), 50 mg C₁₈, and 7.5 mg graphitized carbon black (GCB) per mL extract was used. No significant differences were observed in the results between the different sample preparation versions. QuEChERS took < 10 min per individual sample, or < 1 h for two chemists to prepare 32 pre-homogenized samples, and using LP-GC/TOFMS, < 10 min run time and < 15 min cycle time allowed > 32 injections in 8 h. Overall, > 126 analytes gave recoveries (3 spiking levels) in the range of 70-120% with < 20% RSD. The results indicate that LP-GC/TOFMS for GC-amenable analytes matches UHPLC-MS/MS in terms of sample throughput and turnaround time for their routine, concurrent use in the analysis of a wide range of analytes in QuEChERS extracts to achieve reliable quantification and identification of pesticide residues in foods.

Development of enzyme linked immunoassay for the simultaneous detection of carbaryl and metolcarb in different agricultural products

A direct competitive enzyme linked immunosorbent assay in multi-enzyme tracers format for the simultaneous analysis of carbaryl and metolcarb in agricultural products is described in this study. The concentrations of coating antibodies and enzyme tracer were studied. Under the optimum conditions, the limits of detection of carbaryl and metolcarb were 0.15 microg L(-1) and 1.2 microg L(-1), respectively. Determination of carbaryl and metolcarb in fruit juices and vegetables was accomplished by simple, rapid and efficient extraction methods. Recoveries of spiked samples were great than 70%. Validation of the immunosorbent assay was conducted by comparison of results from high performance liquid chromatography (HPLC). The correlations between the data obtained using multi-enzyme tracers enzyme linked immunosorbent assay and high performance liquid chromatography were good. Results indicated that the new strategy for developing immunoassay for simultaneous quantitative determination of carbaryl and metolcarb residues was suitable in this study.

Comparison of QuEChERS sample preparation methods for the analysis of pesticide residues in fruits and vegetables

This article describes the comparison of different versions of an easy, rapid and low-cost sample preparation approach for the determination of pesticide residues in fruits and vegetables by concurrent use of gas and liquid chromatography (GC and LC) coupled to mass spectrometry (MS) for detection. The sample preparation approach is known as QuEChERS, which stands for "quick, easy, cheap, effective, rugged and safe". The three compared versions were based on the original unbuffered method, which was first published in 2003, and two interlaboratory validated versions: AOAC Official Method 2007.01, which uses acetate buffering, and European Committee for Standardization (CEN) Standard Method EN 15662, which calls for citrate buffering. LC-MS/MS and GC-MS analyses using each method were tested from 50 to 1000ng/g in apple-blueberry sauce, peas and limes spiked with 32 representative pesticides. As expected, the results were excellent (overall average of 98% recoveries with 10% RSD) using all 3 versions, except the unbuffered method gave somewhat lower recoveries for the few pH-dependent pesticides. The different methods worked equally well for all matrices tested with equivalent amounts of matrix co-extractives measured, matrix effects on quantification and chemical noise from matrix in the chromatographic backgrounds. The acetate-buffered version gave higher and more consistent recoveries for pymetrozine than the other versions in all 3 matrices and for thiabendazole in limes. None of the versions consistently worked well for chlorothalonil, folpet or tolylfluanid in peas, but the acetate-buffered method gave better results for screening of those pesticides. Also, due to the recent shortage in acetonitrile (MeCN), ethyl acetate (EtOAc) was evaluated as a substitute solvent in the acetate-buffered QuEChERS version, but it generally led to less clean extracts and lower recoveries of pymetrozine, thiabendazole, acephate, methamidophos, omethoate and dimethoate. In summary, the acetate-buffered version of QuEChERS using MeCN exhibited advantages compared to the other tested methods in the study.

Hydrolysis study and extraction of spiroxamine from soils of different physico-chemical properties

Spiroxamine, 8-(1,1-dimethylethyl)-N-ethyl-N-propyl-1,4-dioxa-spiro [4.5] decane-2-methanamine, is a novel broad-spectrum fungicide from the new class of spiroketalamines widely used in cereals and grapes. In this paper, the hydrolysis of the spiroxamine active substance has been investigated and the extraction procedure from soil samples has been optimized. The progress of degradation in water at a wide pH range (4-14), was continuously monitored by means of reversed phase LC-ESI-MS/MS in the positive ionization mode during 90 d incubation experiment. To establish the degradation kinetics, water solutions were incubated by triplicate in the dark under controlled temperature (20+/-2 degrees C) and the spiroxamine remaining concentration was determined. Pesticide metabolites such as desethyl, despropyl and N-oxide spiroxamine were not detected at significant amounts in all tested conditions and the degradations followed first-order kinetics (r(2)>or=0.979). The faster degradation was observed at both pH 4 and 14 with half-life times of 37 and 10 d, respectively. On the other hand, the spiroxamine fungicide has been determined in two types of soil (silt loam and sandy loam) at different spiked levels. At the level of the highest spiroxamine application rate for agricultural crops (750 g a.i. ha(-1)), recoveries higher than 96.0% were obtained, showing the effectiveness of the proposed methodology.