The Homogeneity study

15/05/2021,

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