Flow-Injection Spectrophotometric Determination of Amino Acids by Using 1,2-Naphthoquinone-4-sulfonate Immobilized on an Ion Exchange Resin

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Abstract
A spectrophotometric flow-injection method based on the immobilization of 1,2-naphthoquinone-4-sulfonate reagent in an anion-exchange Amberlite IRA 904 packed reactor is proposed for the determination of amino acids. The reagent was attached on this solid bed by electrostatic binding between the sulfonate and the ammonium quaternary groups. This solid-phase reactor was used as a source of reagent since it could be desorbed by means of a hydrochloric acid solution. The reagent liberated to the flow system reacts with the amino acids in a thermostated reaction coil to give the corresponding derivatives. The spectrophotometric detection was performed at 480 nm. For glycine, the response was linear up to 1.5 × 10−3 M, the detection limit was 5.3 × 10−4 M, the repeatability 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 in good agreement with those from the standard method for amino acid analysis.