title: Determination of chlormequat and mepiquat in foods by liquid chromatography/mass spectrometry or liquid chromatography/tandem mass spectrometry: interlaboratory study.
abstract: Interlaboratory validation studies have been performed on 2 methods for the determination of chlormequat (CLQ) and mepiquat (MPQ). Both methods used identical extraction procedures and stable isotope internal standardization but differed in the use of liquid chromatography/mass spectrometry (LC/MS) or LC/tandem mass spectrometry (LC/MS/MS) for the determination, the amount of internal standard used, and the expected limit of detection. After addition of deuterated internal standards, CLQ and MPQ were extracted with methanol-water and determined by LC//MS or LC/MS/MS with positive electrospray ionization. Eight European laboratories participated in the LC/MS method study, analyzing mushroom, pear, wheat flour, and fruit puree with residues of CLQ in the range 0.040-1.19 mg/kg and of MPQ in the range 0.041-0.39 mg/kg. For CLQ, the Horwitz ratio (HoRat) values for individual test materials/levels were in the range 0.85-1.13 with a mean of 1.00, showing good method performance. For MPQ, the Ho values for mushroom, pear (both levels), and wheat flour were in the range 0.83-0.94, again indicating good method performance. For the determination of MPQ in infant food (fruit puree) at 0.041 mg/kg, the Ho was 1.7 when a value of 0 reported by one participant was excluded. In the LC/MS/MS study, in which 11 laboratories participated, a separate sample set was analyzed with residues of CLQ in the range 0.007-1.03 mg/kg and of MPQ in the range 0.008-0.72 mg/kg. Ho values for CLQ were in the range 0.27-1.36 and for MPQ in the range 0.51-2.10, all corresponding to acceptable method performance.
authors.affiliation: Federal Institute for Risk Assessment, D-14191 Berlin, Germany.
authors.forename: Lutz
authors.initials: L
authors.lastname: Alder
authors.forename: James R
authors.initials: JR
authors.lastname: Startin
mesh_terms: D002138:Calibration; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D002716:Chlormequat / Q000032:analysis*; D002853:Chromatography, Liquid / Q000379:methods*; D004350:Drug Residues / Q000032:analysis; D005504:Food Analysis; D005506:Food Contamination; D007477:Ions; D013058:Mass Spectrometry / Q000379:methods*; D000432:Methanol / Q000737:chemistry; D015233:Models, Statistical; D010880:Piperidines / Q000032:analysis*; D010937:Plant Growth Regulators / Q000032:analysis; D011786:Quality Control; D012015:Reference Standards; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D021241:Spectrometry, Mass, Electrospray Ionization; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D007477:Ions; D010880:Piperidines; D010937:Plant Growth Regulators; D014867:Water; D002716:Chlormequat; C049449:mepiquat; D000432:Methanol