Use of a replicated Latin square design in a homogeneity test for high purity organic melting point standards

The use of a replicated Latin square design for reference material homogeneity assessment is illustrated by application to a homogeneity study of eight high-purity organic materials certified for melting point. The design controlled for both a three-level location effect and a run effect. Variance components were extracted using mixed effects modelling using a restricted maximum likelihood method. An alternative classical ANOVA calculation is also given. The effect of appreciable numerical rounding by the instrument software was investigated and shown to be acceptable for the particular example. Estimation of the scale of location and run effects showed that in this example the location effect was both statistically and practically significant, while the run effect was not statistically significant at the 95% level of confidence. The design allowed unbiased estimates of between-unit variances in the presence of both interfering effects.