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. # 2006 Wiley Periodicals, Inc., Mass Spec Rev 25: 2006

In this study, the relationship between matrix concentration and suppression of electrospray ionization (matrix effects) was investigated. Ion suppression of pesticides present in QuEChERS extracts was used as an example. Residue-free extracts of four different commodities, avocado, black tea, orange, and rocket (arugula), were fortified with 39 pesticides each. For many of the resulting 156 pesticide/matrix combinations, considerable matrix effects were observed if the coextracted matrix of 8 mg of equivalent sample (in the case of tea: 1.6 mg) was injected with the undiluted extracts. The reduction of these matrix effects was measured at 10 levels of dilution up to 1000-fold. The results obtained indicate a linear correlation between matrix effects and the logarithm of matrix concentration (or dilution factor) until the zero-effect level of further dilution was reached. Using the logarithmic equations, it could be shown that a dilution of extracts by a factor of 25-40 reduces ion suppression to less than 20% if the initial suppression is ≤80%. For stronger matrix effects or complete elimination of suppression, higher dilution factors were needed. The observed correlation was independent from the two instrument platforms used, but the degree of matrix effects differed slightly between the two mass spectrometers in this study.

This study systematically compares matrix effects in liquid chromatography (LC) coupled by electrospray ionization (ESI) in the positive mode with tandem mass spectrometry (MS/MS) for 129 pesticides in 20 plant matrixes. In total, 2388 analyte/matrix combinations were evaluated. Permanent postcolumn infusion (PCI) of analyte standards was used to quantify matrix effects over the whole chromatographic run time. This allowed the analyte signal suppression or enhancement, by different coeluting matrix components, to be assessed throughout the duration of an entire chromatographic run, i.e., independent of a specific retention time. Matrix effects occurring at a certain retention time in one matrix were surprisingly similar for different analytes with diverse physicochemical properties. On the basis of this finding, a new approach for matrix effect compensation in multiresidue analysis was developed in which one single monitor substance is permanently added postcolumn. Signal intensities of all analytes obtained by LC-MS/MS analysis of sample extracts are then corrected for the matrix effect recorded by the monitor substance. With the use of this approach, strong matrix effects could be reduced and apparent recoveries increased from 45% to 85% on average. With dependence on the particular sample matrix, between 69% and 100% of the analytes showed recoveries between 60% and 140% after correction. Thus this approach may significantly reduce the number of cases in which standard addition is required to confirm violations of maximum residue levels.

This study describes the validation and application of two independent analytical methods for the determination of glyphosate in breast milk. They are based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS), respectively. For LC-MS/MS, sample preparation involved an ultrafiltration followed by chromatography on an anion exchange column. The analysis by GC-MS/MS involved an extraction step, cleanup on a cation exchange column, and derivatization with heptafluorobutanol and trifluoroacetic acid anhydride. Both methods were newly developed for breast milk and are able to quantify glyphosate residues at concentrations as low as 1 ng/mL. The methods were applied to quantify glyphosate levels in 114 breast milk samples, which had been collected from August to September of 2015 in Germany. The mothers participated at their own request and thus do not form a representative sample. In none of the investigated samples were glyphosate residues above the limit of detection found.

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