Determination of quaternary ammonium compound residues in fruits and vegetables by QuEChERS following LC-MS/MS analysis

Ellen Scherbaum Kontakt, Julia Hepperle, Dr. Eberhard Schüle, Chemisches und Veterinäruntersuchungsamt (CVUA) Stuttgart

A simple and fast method to determine residues of quaternary ammonium compounds (QAC) in fruit and vegetable samples is presented. The analytes were extracted applying the frequently used QuEChERS method. Analysis was performed by liquid chromatography-electrospray tandem mass spectrometry (LC-ESI-MS/MS) in the positive mode using a triple quadrupole instrument. The method was validated for the following representative matrices: cucumber (high water content), raisin (high sugar content), lemon (sour) and wheat (dry) at 0.1 mg kg-1 level. The method validation resulted in satisfying recoveries and relative standard deviations (RSDs) for all QAC. In cucumber, raisin, lemon and wheat matrices, recoveries ranged between 88 and 104% and RSDs ranged between 1.1 and 9.8%. All analytes were regularly detected at very low level (<0.005 mg kg-1) in blank sample material and even when only solvent was injected. Therefore, the reporting limit was set to 10 µg kg-1. Our results demonstrate that determining QAC can easily be integrated in routinely conducted QuEChERS extraction followed by LC-MS/MS analysis. In a final step we proved the method's performance analyzing conventional and organic grown samples from the common market.

Quaternary ammonium compounds (QAC) are surface active substances containing a quaternary cationic nitrogen atom, substituted by alkyl chains of varying length. The important representatives benzalkonium chlorides (BAC) and didecyldimethylammonium chloride (DDAC) are shown in figure 1. QAC are enriched in cell membranes of living organisms and can impair cell membrane functions. Due to these characteristics, QAC are used as biocides, pesticides, disinfectants, wood preservatives and additives for technical applications, furthermore as ingredients in human and veterinary medicinal products and cosmetics. Additionally, plant protection products like plant strengtheners can contain QAC not as active ingredients but as additives. The authorization of such plant strengtheners has meanwhile been withdrawn within Germany.

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