SOME OBSERVATIONS ON THE AUTOMATION BY FLOW-INJECTION ANALYSIS OF THE SPECTROPHOTOMETRIC DETERMINATION OF AMINO-ACIDS AND PROTEINS WITH ORTHO-PHTHALALDEHYDE

Automation by flow injection analysis with spectrophotometric detection of the determination of total amino acids and proteins with o-phthalaldehyde is not straightforward. The use of spectrophotometry, instead of spectrofluorimetry, and of N-acetyl-L-cysteine, instead of the conventional mercaptoethanol is advantageous because of the lower variability of absorptivities with respect to fluorescence yields, and the larger stability of the derivatives. Under adequate working conditions and with leucine as reference, the procedure can be used for the evaluation of total amino acids. A similar procedure is proposed for the analysis of proteins in a sample. Limits of detection are almost-equal-to 1 x 10(-5) M for amino acids, and almost-equal-to 1 x 10(-6) M for proteins, respectively.