Determination of residues of the plant growth regulator chlormequat in pears by ion-exchange high performance liquid chromatography-electrospray massspectrometry

We report a method which we have used routinely for the determination of ch lormequat residues in pears. After extraction with methanal, determination was performed, without clean-up, by ion-exchange HPLC using an SCX column e luted with aqueous ammonium formate-methanol, and HPLC-MS with an electrosp ray interface. MS and MS-MS were employed concurrently, using selected ion monitoring and selected reaction monitoring, respectively, of the Cl-35 and Cl-37 isotopes of the chlormequat cation and the CID transitions of each o f these precursors to the common product ion at mit 58. The method was suit able for determinations at concentrations of chlormequat cation of 0.04 mg kg(-1). Concentrations determined using the four signals were in goad agree ment (mean RSD 3%). The mean recovery of chlormequat cation at 0.16 mg kg(- 1), measured using the mit 122-->,58 signal, was 86% (RSD 7%) under repeata bility conditions and 88% (RSD 15%) in routine application of the method ov er a 3 month period. Analysis of an in-house reference sample of pears, sim ilarly analysed over the 3 month period, gave an RSD of 10% with a mean of 0.14 mg kg(-1). Mean recovery at 0.016 mg kg-l,under repeatability conditio ns on two occasions, was 101% (RSD 6%) and 56% (RSD 12%).