1989 Volume 38 Issue 11 Pages 596-600
Magnesium phosphate glasses containing silver oxide show a response for monovalent anions and ammonia with near Nernstian slope. Ammonia and hydrogen peroxide are released by enzymatic reaction of L-amino acids with L-amino acid oxidase. By combining a flow cell composed by this glass membrane and a CPG-10 glass beads column which immobilized with L-amino acid oxidase, L-amino acid can be enzymatically determined with the potentiometric sensor which gives a specific response for liberated ammonia. The chromatographic system employed comprised a HPLC pump, a sintered ceramic filter, a Rheodyne sample injector, a combination of a Toso aminopack column and a treated enzyme column, and a DKK ion-selective flow cell with some improvements. The aminopack column was maintained at 50°C, but the treated enzyme column was operated between 30 and 50°C. When eluents for L-amino acids were applied to 1 mM sodium citrate solutions of pH 5.00, 8.65 and 9.16, these peak heights were linearly related to the concentration of L-amino acids ranging from 10-5 to 5 × 10-3 M, for injections of 100 μl samples. After three months, the treated enzyme column retained about 90% of the original sensitivity. The sensitivity obtained was of the same order as that of the ninhydrin method, while the orthophthalaldehyde method was somewhat more sensitive.
