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 chlormequat (CCC) in pears and pear concentrates is described. The method is based on sample clean-up using an SPE strong cationic exchange (SCX) cartridge followed by analysis on a benchtop liquid chromatograph coupled to an atmospheric pressure electrospray ionisation mass spectrometer (LC-ESI-MS). The instrument is equipped with a weak cationic exchange (WCX) column. For quantification, ionsm/z 122 and 124, representing the chloro isotopes of the molecular 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 concentrates in the range of 90–93%. The dynamic range covers concentrations from 10 to 500 μg kg−1 (ppb) with a correlation coefficient of r=0.999. During 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 of detection (LOD) is 3 ppb (3 S/N) and the limit of quantitation (LOQ) is 10 ppb. Residue levels in pears purchased from a local supermarket in December 1998 and January 1999 were as high as 8 mg kg−1 (8 ppm). The method can also be applied to the determination of CCC in other fruits and concentrates e.g. apples and grapes.