Homogeneity and concentration ranges

Extreme care must be taken to ensure that the bulk sample from which the laboratory or test samples are taken is stable and homogeneous—this is particularly important if spiked samples are provided. 

The homogeneity should be established by testing a representative number of laboratory samples taken at random using either the proposed method of analysis or other appropriate tests such as UV absorption, refractive index, etc. The penalty for inhomogeneity is an increased variance in analytical results that is not due to intrinsic method variability. 

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