Development of a candidate certified reference material of cypermethrin in green tea
Author: Della W.M. Sin and Pui-kwan Chan and Samuel T.C. Cheung and Yee-Lok Wong and Siu-kay Wong and Chuen-shing Mok and Yiu-chung Wong
This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg−1 and the associated expanded uncertainty was 14 μg kg−1. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.