Determination of the plant growth regulator chlormequat in food by liquid chromatography-electrospray ionisation tandem mass spectrometry

A confirmatory method for the determination of trace levels of chlormequat in a variety of different food matrices was developed. It entails a single clean-up step over a solid-phase cation exchange resin and subsequent liquid chromatography-electrospray ionisation tandem mass spectrometry using a stable isotopically labelled internal standard. Mass spectral acquisition was done in selected reaction monitoring mode, selecting the transitions from both the Cl-35 and the Cl-37 isotope of chlormequat. Recoveries after extraction and clean-up, determined with radio-labelled chlormequat and averaged over the spiking range (16-65 mu g kg(-1)) in four different commodities, were within 88-96%, with a coefficient of variation better than 8%. The method can be applied to pears, pear juice concentrates, fruit purees, and cereal products, with typical limits of detection for chlormequat estimated at 2-5 mu g kg(-1). A survey of different food commodities revealed that chlormequat was detectable - albeit at very low levels - in many of the food samples analysed, with the highest concentration recorded in pears purchased in Switzerland and of South African origin (5.5 mg kg(-1)). Measurements were also conducted on two LC-MS instruments and demonstrate the versatility and robustness of the method and its applicability to instruments of different ion source design. (C) 2000 Elsevier Science B.V. All rights reserved.