Most laboratories which responded to the 1989 amino acid analysis survey used either post-column ninhydrin-based amino acid analysis systems (47%) or pre-column PTC-based methods (44%). Facilities were asked to analyze AAA1 at either 5 microgram and 0.5 microgram levels, or at 0.5 microgram and 0.2 microgram levels depending upon the sensitivity of the method used. Overall results demonstrated similar performance of the ninhydrin and PTC methods at the two higher levels. The best results were obtained with the larger amounts of AAA1 which was beta-lactoglobulin, alpha chain from Sigma Chemical Co. Average accuracy was near 90% for the higher amounts and about 84% for the intermediate amount. Precision was 18-20% SD for the higher amount and 26% SD for the intermediate load level. PTC-amino acid analysis was the most common high sensitivity method, and it was used by 80% of those facilities that analyzed AAAl at the 0.2 microgram level.
Results from the prehydrolyzed sample, ABRF89AAA2, exhibited less variability, but more error than the AAA1 data. These results illustrate the contribution of the hydrolysis procedure to errors in amino acid analysis.
Pyridylethyl cysteine in AAA2 was determined by 56% of the responding facilities. The average accuracy was 87%. Less than half (44%) of the respondents measured cysteine in the unmodified sample, AAA1. Of the laboratories that analyzed cysteine in AAA1, about 80% carried out performic acid oxidation and quantified cysteic acid with about ~3% accuracy.
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Created: 10th August 1995
Last modified: 10th August 1995