Between-vial homogeneity study

For materials destroyed during analysis, it is not possible to measure all individual samples. If the trend in preparation is continuous and known, an extrapolation on the uncertainty of the certified value can be attempted but this would also decrease the analytical value of the CRM. In the majority of situations drifts or trends are not foreseen and known. Therefore, it will be necessary to measure samples all over the packaging procedure. The between-vial homogeneity study has the objective to verify that no difference exists in the parameter of interest (concentration of the element or substance) between sets. It may also verify that the matrix composition remains similar. The objective of the within-vial study was to verify the homogenisation procedure and estimate the minimum sample intake if necessary. The between-vial homogeneity assesses that the material is suitable for comparability between laboratories. 

All tests must be performed in the most repeatable way. Again experiments should be done in parallel all extractions in parallel, if possible one calibration. If necessary and possible (stability problems), all extracts produced in parallel should be stored in the dark at low temperatures. Purification and final determination should be done also in parallel. It is preferable to study the between-vial homogeneity with the same sample intake as for the within-vial test. This should allow more direct comparisons of results. 

---