M. Vela et al., FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATION OF AMINO-ACIDS BY USING 1,2-NAPHTHOQUINONE-4-SULFONATE IMMOBILIZED ON AN ION-EXCHANGE RESIN, Analytical letters, 31(2), 1998, pp. 313-331
A spectrophotometric flow-injection method based on the immobilization
of 1,2-naphthoquinone-4-sulfonate reagent in an anion-exchange Amberl
ite IRA 904 packed reactor is proposed for the determination of amino
acids. The reagent was attached on this solid bed by electrostatic bin
ding between the sulfonate and the ammonium quaternary groups. This so
lid-phase reactor was used as a source of reagent since it could be de
sorbed by means of a hydrochloric acid solution. The reagent liberated
to the flow system reacts with the amino acids in a thermostated reac
tion coil to give the corresponding derivatives. The spectrophotometri
c detection was performed at 480 nm. For glycine, the response was lin
ear up to 1.5 x 10(-3) M the detection limit was 5.3 x 10(-4) M, the r
epeatability 0.4% and the reproducibility 5.4%. The method was applied
to the analysis of some amino acids in several pharmaceutical samples
. Results obtained were ill good agreement with those from the standar
d method for amino acid analysis.