APPARATUS FOR THE FLOW-INJECTION ANALYSIS OF L-CYSTINE

An apparatus for the flow injection analysis of L-cystine using an amperometric detector composed of a glassy carbon electrode and a silver wire electrode was constructed, and the optimum conditions were investigated. The carrier solution used was a mixture of 0.6 M H3BO3, 0.1 M Na2B4O7 . 10H2O and 0.15 M Na2SO3, at a flow rate of 3.0 ml/min. A hundred microliters of L-cystine solution (10(-4) approximately 10(-3) M) was injected into the flow system at an applied potential of 0.55 V, and the indicator current was recorded after the reaction with sulfite in the reaction coil (150 CM). L-CyStine (0.360 approximately 0.841 mug) was determined with a relative error of 0.5% and RSD of 0.7%. This apparatus made it possible to determine 30 samples in one hour.