Determination of chlormequat residues in pears and pear concentrates by benchtop LC-ESI-MS

A fast, simple and robust method for the routine determination of chlormequ at (CCC) in pears and pear concentrates is described. The method is based o n sample clean-up using an SPE strong cationic exchange (SCX) cartridge fol lowed by analysis on a benchtop liquid chromatograph coupled to an atmosphe ric pressure electrospray ionisation mass spectrometer (LCESI-MS). The inst rument is equipped with a weak cationic exchange (WCX) column. For quantifi cation, ions mh 122 and 124, representing the chloro isotopes of the molecu lar ion, are monitored. Recoveries for chlormequat at three levels (50, 100 , 250 ppb) from pears are in the range of 81-85 %, and from pear concentrat es in the range of 90-93 %. The dynamic range covers concentrations from 10 to 500 mu g kg(-1) (ppb) with a correlation coefficient of r = 0.999. Duri ng validation, the reproducibility (RSD) for the standard solution is found to be 4.3 % (n=8; within one day) and 6.0% (n=16, day-to-day), the limit o f detection (LOD) is 3 ppb (3 S/N) and the limit of quantitation (LOQ) is 1 0 ppb. Residue levels in pears purchased from a local supermarket in Decemb er 1998 and January 1999 were as high as 8 mg kg(-1) (8 ppm). The method ca n also be applied to the determination of CCC in other fruits and concentra tes e.g. apples and grapes.