The Homogeneity study
Extract from the international harmonized protocol for the proficiency testing of (chemical) analytical laboratories (2006)
by Thompson M, Ellison WLR, Wood R, (IUPAC technical report); https://doi.org/10.1351/pac200678010145
A recommended procedure for testing a material for sufficient homogeneity
The procedure to be followed by the Laboratory preparing proficiency test materials is as follows:
- Prepare the whole of the bulk material in a form that is thought to be homogeneous, by an appropriate method. Divide the material into the containers that will be used for dispatch to the participants.
- Select a minimum (n) of 10 containers strictly at random.
- Separately homogenise the contents of each of the n selected containers and take two test portions. Analyse the 20 test portions in a random order under repeatability conditions by an appropriate method. The analytical methcd used must be sufficiently precise to allow a satisfactory estimation of Ss.
- Form an estimate (Ss^2) of the analytical variance by one-way analysis of variance (ANOVA), without exclusion of outliers.
- Report values of mean value, Ss, Sa, n and the result of the F-test
- If S_pt is the target value for standard deviation for the proficiency test at analyte concentration, the value of Ss/S_pt should be less than 0.3 for sufficient hanogeneity.
For more information:
- ISO 17043:2010 - Conformity assessment — General requirements for proficiency testing
- ISO 13528:2015 - Statistical methods for use in proficiency testing by interlaboratory comparison
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