title: S1 certification of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in a candidate certified reference material (organochlorine pesticides in tea) by isotope dilution gas chromatography-mass spectrometry.
abstract: This paper presents the certification of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in a candidate tea certified reference material (code: GLHK-11-03) according to the requirements of the ISO Guide 30 series. Certification of GLHK-11-03 was based on an analytical method purposely developed for the accurate measurement of the mass fraction of the target analytes in the material. An isotope dilution mass spectrometry (IDMS) method involving determination by (i) gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS) and (ii) gas chromatography-electron ionization-high-resolution mass spectrometry (GC-EI-HRMS) techniques was employed. The performance of the described method was demonstrated through participation in the key comparison CCQM-K95 "Mid-Polarity Analytes in Food Matrix: Mid-Polarity Pesticides in Tea" organized by the Consultative Committee for Amount of Substance-Metrology in Chemistry in 2012, where the study material was the same as the certified reference material (CRM). The values reported by using the developed method were in good agreement with the key comparison reference value (KCRV) assigned for beta-endosulfan (727 ± 14 μg kg(-1)) and endosulfan sulfate (505 ± 11 μg kg(-1)), where the degree of equivalence (DoE) values were 0.41 and 0.40, respectively. The certified values of alpha-endosulfan, beta-endosulfan, and endosulfan sulfate in dry mass fraction in GLHK-11-03 were 350, 730, and 502 μg kg(-1), respectively, and the respective expanded uncertainties, due to sample inhomogeneity, long-term and short-term stability, and variability in the characterization procedure, were 27 μg kg(-1) (7.8 %), 48 μg kg(-1) (6.6 %), and 33 μg kg(-1) (6.6 %).
authors.affiliation: Government Laboratory, 7/F., Ho Man Tin Government Offices, 88 Chung Hau Street, Ho Man Tin, Kowloon, Hong Kong Special Administrative Region, China.
authors.forename: Della Wai-Mei
authors.initials: DW
authors.lastname: Sin
authors.forename: Yee-Lok
authors.initials: YL
authors.lastname: Wong
authors.forename: Eddie Chung-Chin
authors.initials: EC
authors.lastname: Cheng
authors.forename: Man-Fung
authors.initials: MF
authors.lastname: Lo
authors.forename: Clare
authors.initials: C
authors.lastname: Ho
authors.forename: Chuen-Shing
authors.initials: CS
authors.lastname: Mok
authors.forename: Siu-Kay
authors.initials: SK
authors.lastname: Wong
mesh_terms: D002138:Calibration; D005591:Chemical Fractionation; D004726:Endosulfan / Q000031:analogs & derivatives* / Q000032:analysis* / Q000592:standards; D005504:Food Analysis / Q000379:methods / Q000592:standards; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods / Q000592:standards*; D006843:Hydrocarbons, Chlorinated / Q000032:analysis; D007536:Isomerism; D010573:Pesticide Residues / Q000032:analysis; D010575:Pesticides / Q000032:analysis* / Q000592:standards; D011865:Radioisotope Dilution Technique; D012015:Reference Standards; D012680:Sensitivity and Specificity; D013662:Tea / Q000737:chemistry*
chemical_list: D006843:Hydrocarbons, Chlorinated; D010573:Pesticide Residues; D010575:Pesticides; D013662:Tea; C544689:endosulfan sulfate; D004726:Endosulfan