Inter- and intralaboratory variation in amino acid composition of casein, soy flour, and fish flour was examined for 5 cooperating laboratories, utilizing ion exchange chromatographic analyses for amino acids. Duplicate analyses within laboratories exhibited coefficients of variation of 3.7 to 4.4%. Hydrolysis was observed to affect amino acid recoveries to a significant degree, with some amino acids affected to greater extents than others. Laboratories utilizing Moore-Stein type analytical procedures did not appear to be more precise than those using the Piez-Morris method. Adjustment of data to constant total recovery values reduced interlaboratory variation considerably and suggested that recovery constants may be of value in comparing data from different laboratories. Results indicated that different laboratories employing varying analytical procedures may produce practically identical results from a standard sample, although variation may be observed due to characteristics of a specific system. Most variation in results was likely due to sample manipulations rather than to analysis per se.
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Knipfel et al. (1971) studied this question.