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.

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The dietary intake of Omega-3 (omega-3) and Omega-6 (omega-6) fatty acids (FA) may influence the development of atopic diseases. Based on the results of two dietary surveys, the intake of omega-3-FA and omega-6-FA in West Germany in 1985-1989 and in Dresden, East Germany in 1988-1989 and 1990-1991 was estimated. The intake of omega-6-FA but not of omega-3-FA was slightly higher in the West German population before 1990, mainly because of a higher intake of vegetable oil. Immediately after 1990 the omega-6-FA-intake in the observed East German sample increased because of an increase in the consumption of margarine [from a mean of 16 (SD 17) to 38 (24) g day-1]. Additional information indicates that, in contrast, East German infant formulas contained higher amounts of omega-6-FA (linoleic acid) and lower amounts of omega-3-FA (alpha-linolenic acid) than West German formulas. Whether there is a causal relation between the amounts of omega-6-FA and omega-3-FA consumed and the prevalence of atopy in children from East and West Germany remains to be clarified.

Pesticide residue analysis is an important part of food quality control. Three of the most widely used methods are the DFG S19 (extraction with acetone), the ChemElut method (extraction with methanol), and QuEChERS (quick, easy, cheap, effective, rugged, safe; acetonitrile-based). Despite many developments in the field of sample preparation, matrix effects are still one of the most disturbing problems in routine analysis. In this study, we compare the matrix effects in LC-MS analysis after using these three methods in pesticide analysis. Using postcolumn infusion, we were able to visualize all suppressions over the whole chromatogram in matrix-effect profiles. Recently, we also presented a system for the determination of up to 300 pesticides from various kinds of fruit and vegetables. For the measurement, we injected an aliquot of a raw acetonitrile extract. The subsequent cleanup was carried out fully automated by a multidimensional LC. Matrix compounds and analytes are separated in the first dimension on a hydrophilic interaction LC column. In this study, we also compared this new approach with the classical methods. The matrix-effect profiles showed less suppression with the hydrophilic interaction LC-based cleanup. A final evaluation of the partitioning steps of all methods confirmed the benefits of the chromatographic cleanup approach.