Determination of sampling constants for selenium in biological reference materials by neutron activation

Summary A cyclic instrumental neutron activation analysis method has been used to calculate sampling constants and to evaluate homogeneity for Se in five biological reference and certified reference materials, namely NRC lobster hepatopancreas (RM TORT-1), IAEA horse kidney (RM-H8), and NIST bovine liver (SRM-1577a), oyster tissue (SRM-1566) and mixed diet (RM-8431). The between-weight-range heterogeneity has been observed to be no greater than the within-weight-range heterogeneity. The subsampling standard deviation (S _s) has been found to be less than the measurement standard deviation (S _m) for H-8 (>5 mg sample) and TORT-1 (>50 mg). For 1577a, S _s is almost equal to S _m; while S _s is 2–3 times higher than S _m for the other two materials. The sampling constants varied between 0.04 and 3.0 g for four materials while the mixed diet had a value of 31 g.