title: Accurate analysis of urea in milk and milk powder by isotope dilution gas chromatography-mass spectrometry.
abstract: A high order method for measuring urea concentrations in milk and milk powder was developed. The method can be applied to certify the concentration of urea in some new milk and milk powder CRMs. This high accurate method for analysis of milk is valuable given the inherent challenges associated with the complexity of the sample matrix. A measurement procedure based on gas chromatography/isotope dilution mass spectrometry (GC/IDMS) was developed. Samples were pre-treated with acetonitrile to remove proteins and the method was applied to determine urea concentrations in milk and milk powder. Excellent precision was obtained, with within- and between-set coefficients of variation of 0.15-0.46 and 0.18-0.65%, respectively. The measurement uncertainty is evaluated. The method can trace to mass.
authors.affiliation: National Institute of Metrology, No. 18 Beisanhuan Donglu, Chaoyang Dist, Beijing 100013, PR China. xhdai_75@iccas.ac.cn
authors.forename: Xinhua
authors.initials: X
authors.lastname: Dai
authors.forename: Xiang
authors.initials: X
authors.lastname: Fang
authors.forename: Fuhai
authors.initials: F
authors.lastname: Su
authors.forename: Mengrui
authors.initials: M
authors.lastname: Yang
authors.forename: Hongmei
authors.initials: H
authors.lastname: Li
authors.forename: Jian
authors.initials: J
authors.lastname: Zhou
authors.forename: Ruifeng
authors.initials: R
authors.lastname: Xu
mesh_terms: D000097:Acetonitriles; D000818:Animals; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D007553:Isotope Labeling / Q000379:methods*; D016014:Linear Models; D000432:Methanol; D008892:Milk / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014508:Urea / Q000032:analysis*
chemical_list: D000097:Acetonitriles; D014508:Urea; D000432:Methanol; C032159:acetonitrile