CCQM-K107: Total elements and selenomethionine in human serum Final Report

A total of eleventh NMIs participated in CCQM-K107. The sample is frozen human serum prepared from blood obtained from the Royal Surrey County Hospital. It HSA been stored in 2 mL plastic screw-cap Nalgene cryovial, each containing 1.1 mL serum, at -70°C ± 10°C in the dark. The serum sample HSA been tested for homogeneity with 0.5g subsamples analyzed by ID-ICP-MS. Cu uhom = 0.98%; Se uhom = 1.88% and Zn uhom = 1.84%. Short term stability data (storage at -20 °C and 40 °C for 2 weeks, 1 month) suggested that the sample should be transported frozen. Long term stability data showed no significant change for the material occurred in the Cu, Zn and Se content. Homogeneity testing for electrolytes was performed by PTB using microwave digestion and ion chromatography. LGC did perform homogeneity testing for Fe, Mg and SeMet using ICP-IDMS and HPLC-ICP-IDMS, respectively, before the sample was distributed. Participants were sent a number of vials according to their response to the questionnaire distributed by the coordinating laboratory. An average of approximately 5-10 vials was sent to each participant. All samples were shipped in dry ice. For the determination of total K, six (out of nine) of the key comparison participants used microwave acid digestion for sample preparation whilst LGC, HSA and UME used sample dilution with dilute nitric acid. The NIMT mass fraction for Fe is significantly high biased from those reported by the rest of the participants. The first presentation of results to the working group was followed up by discussions with NIMT, which identified problems related to relatively high procedural blanks.