J. Saurina et S. Hernandezcassou, CONTINUOUS-FLOW SPECTROPHOTOMETRIC DETERMINATION OF AMINO-ACIDS WITH 1,2-NAPHTHOQUINONE-4-SULFONATE REAGENT, Analytica chimica acta, 283(1), 1993, pp. 414-420
A completely continuous-flow method for amino acid determination is pr
oposed. The spectrophotometric detection is based on the reaction betw
een amino acids and 1,2-naphthoquinone-4-sulphonic acid (NQS) in basic
sodium carbonate-sodium hydroxide medium (pH 10). The reaction was de
veloped on-line because NQS solutions are unstable in this medium. Phe
nylalanine (Phe) was chosen as a model amino acid to develop the metho
d. The influence on the absorbance of different variables (pH, buffer
and reagent concentrations, temperature, reaction coil length and flow
-rate) were studied. For Phe at 470 nm, the calibration graph was line
ar up to 1.5 x 10(-4) M, the reproducibility was 2.5% and the limit of
detection was 2 x 10(-6) M. The sample throughput was 40 h-1. Measure
ments of reaction product spectra were carried out in the range 290-59
0 nm. Spectral differences for nineteen amino acids derivatives were s
tudied by using principal component analysis and cluster analysis. On
this bases a spectral classification can be made.