Development of a QuEChERS-Based Method for the Simultaneous Determination of Acidic Pesticides, Their Esters, and Conjugates Following Alkaline Hydrolysis.

An analytical procedure was developed allowing the simultaneous determination of acidic pesticides and their conjugates by addition of an alkaline hydrolysis step into the European Union (EU) version of the QuEChERS method. The procedure resulted additionally in hydrolysis of most esters of phenoxy acids. On the basis of information from metabolism studies and the hydrolytic conditions employed in supervised field trials as well as results on the influence of physical and chemical parameters (temperature, time, type of solvent, type of matrix), alkaline hydrolysis for 30 min at 40 °C was deemed a good compromise for the determination of residues of 2,4-D, dichlorprop, fluazifop, haloxyfop, MCPA, and MCPB. The applicability of the proposed method was tested by analyzing food samples with incurred residues in six German laboratories not involved in method development. Up to 6 times higher residues are measured by using the QuEChERS extraction procedure with the newly developed alkaline hydrolysis step.

Fast multiresidue screening of 300 pesticides in water for human consumption by LC-MS/MS.

The study tested the determination of 300 pesticides in mineral water at levels of 0.1 and 1.0 microg/L. Measurements were conducted by direct sample injection into a liquid chromatograph coupled to a tandem mass spectrometer without any sample enrichment and/or cleanup. Two separate injections enabled the recording of two transitions per analyte (600 selected reaction monitoring transitions in total). For 285 analytes the sensitivity of direct sample injection (100 microL) was sufficient to quantify residues at 0.1 microg/L. All remaining pesticides were detected at 1.0 microg/L. Calibration functions were linear for more than 80% of analytes. Signal suppression or enhancement compared with signals in high-performance liquid chromatography water was equal to or smaller than 20% for 240 analytes. Even the largest matrix-induced suppression did not result in the disappearance of peaks. Combining the results of seven mineral waters, the relative standard deviation of "recovery" was 20% or less for 87% of the substances. A second transition for confirmatory purposes was often available. Consequently, the proposed direct injection of samples without any sample enrichment and/or cleanup is suitable for screening of many pesticides in mineral and drinking water.

Residue analysis of 500 high priority pesticides: better by GC-MS or LC-MS/MS?

This overview evaluates the capabilities of mass spectrometry (MS) in combination with gas chromatography (GC) and liquid chromatography (LC) for the determination of a multitude of pesticides. The selection of pesticides for this assessment is based on the status of production, the existence of regulations on maximum residue levels in food, and the frequency of residue detection. GC-MS with electron impact (EI) ionization and the combination of LC with tandem mass spectrometers (LC-MS/MS) using electrospray ionization (ESI) are identified as techniques most often applied in multi-residue methods for pesticides at present. Therefore, applicability and sensitivity obtained with GC-EI-MS and LC-ESI-MS/MS is individually compared for each of the selected pesticides. Only for one substance class only, the organochlorine pesticides, GC-MS achieves better performance. For all other classes of pesticides, the assessment shows a wider scope and better sensitivity if detection is based on LC-MS.

Applicability of gradient liquid chromatography with tandem mass spectrometry to the simultaneous screening for about 100 pesticides in crops.

A method was developed for screening crops for a range of pesticide residues by liquid chromatography/tandem mass spectrometry (LC/MS/MS). A complete set of LC, electrospray ionization (ESI), and tandem MS acquisition parameters was established for the determination of 108 analytes; these parameters were used for the simultaneous acquisition of 98 analytes in the positive ESI mode and 10 analytes in an additional MS/MS method in the negative ESI mode. The entire procedure involves extraction of residues with methanol-water and partition into dichloromethane. The utility of the method is demonstrated by the analysis of crops of 5 matrix types (water-containing, acidic, dry, sugar-containing, and fatty). Of 108 pesticides/metabolites tested, 104 showed sufficient stability in most matrixes for determination by LC/MS/MS. These analytes belong to 20 chemical classes, which demonstrate the general applicability of the method for multiclass analysis. By using matrix-matched standards, 67 compounds could be determined in most matrixes with recoveries of 70-120% and a relative standard deviation of < or = 25% at the 0.01 mg/kg level.