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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This study investigates to which extent the design of electrospray ion sources influences the susceptibility to matrix effects (MEs) in liquid chromatography–tandem mass spectrometry (LC–MS/MS). For this purpose, MEs were measured under comparable conditions (identical sample extracts, identical LC column, same chromatographic method and always positive ion mode) on four LC–MS/MS instrument platforms. The instruments were combined with five electrospray ion sources, viz. Turbo Ion Spray, Turbo VTM Source, Standard ESI, Jet Stream ESI and Standard Z‐Spray Source. The comparison of MEs could be made at all retention times because the method of permanent postcolumn infusion was applied. The MEs ascertained for 45 pesticides showed for each electrospray ion source the same pattern, i.e. the same number of characteristic signal suppressions at equivalent retention times in the chromatogram. The Turbo Ion Spray (off‐axis geometry), Turbo VTM Source (orthogonal geometry) and the Standard Z‐Spray Source (double orthogonal geometry) did not differ much in their susceptibility to MEs. The Jet Stream ESI (orthogonal geometry) reaches a higher sensitivity by an additional heated sheath gas, but suffers at the same time from significantly stronger signal suppressions than the comparable Standard ESI (orthogonal geometry) without sheath gas. No relation between source geometry and extent of signal suppression was found in this study. Copyright © 2012 John Wiley & Sons, Ltd.

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Glyphosate is the most commonly used herbicide worldwide. To identify glyphosate and its metabolite, aminomethylphosphonic acid (AMPA), in the difficult-to-analyze matrix of tea, new methods were developed. The main emphasis was placed on the cleanup procedure. Two different solid-phase extraction methods were tested and evaluated: one with molecularly imprinted polymers, and the other with immobilized titanium dioxide. The optimization was carried out on the basis of aqueous standard solutions and spiked tea extracts. Validated results were presented for pipet tips that contained immobilized titanium dioxide. After the extraction of glyphosate from tea samples using hydrochloric acid (0.1), glyphosate and AMPA were concentrated on the adsorbent by pipetting up and down several times without changing the tip. The elution was carried out subsequent to a washing step with 5 ammonia. The extract was derivatized with 2,2,2-trifluoroacetic acid and 2,2,2-trifluoroethanol and then analyzed by GC with MS detection in the negative chemical ionization mode. Quantification was carried out in the selected-ion monitoring mode based on the m/z ratio of characteristic ions due to the ionization process. For glyphosate m/z = 370 was applied, and m/z = 351 for AMPA. The detection limit was 0.03 mg/kg tea for glyphosate and 0.006 mg/kg tea for AMPA. The recoveries for the tested working range (0.1 to 2.8 mg/kg tea) were low but constant at 14 and 12, respectively. Altogether, the method presented here can be carried out easily and quickly, and it gives reliable information on the presence of the analytes in a sample. Quantification is also possible using standard addition.