Collaborative test of the fluorimetric determination of selenium in a test solution, milk powder and bovine liver

Results are reported for an inter-laboratory test conducted to assess precision (repeatability, reproducibility) and accuracy of a collaborative method for the fluorimetric determination of selenium (Se). The seven participating laboratories analysed one test solution, four samples of milk powder and two samples of freeze-dried bovine liver. Each set of samples comprised three duplicates: two colorant-disguised milk powders and one code disguised freeze-dried bovine liver. Two of the milk powders were enriched with 90.7 micrograms/kg Se as seleno-DL-methionine. One set of results had to be rejected because the laboratory involved did not adhere to the collaborative method. Results from a second laboratory contained both stragglers and outliers. The five remaining laboratories performed the method satisfactory. Results from these laboratories were statistically evaluated according to ISO 5725. The average coefficient of variation within a laboratory (repeatability) was 4.8% and between laboratories (reproducibility) 6.0% for the milk powder and bovine liver samples. Recovery for the test solution, target value 120 micrograms Se/1, was 96% and the average recovery for the Se enriched milk powder was 88%. The mean result for the milk powder was 98.9 micrograms/kg (n = 10), coefficient of variation (CV) 6.7%, and for Se enriched milk powder 178.3 micrograms/kg, coefficient of variation (CV) 3.6%. For freeze-dried bovine liver, these results were 238.4 micrograms/kg and 4.1% respectively.