An automatic flow-injection analysis system for determining phosphate ion in river water using pyruvate oxidase G (from Aerococcus viridans)

An automated flow-injection system combining a pyruvate oxidase reaction an d chemiluminescence for the detection of phosphate ion in river water has b een developed. In this research, we used pyruvate oxidase G (PyrOxG), from Aerococcus viridans, immobilizing it on N-hydroxysuccinicacidimido beads wi thout a cross-linker. In this sensor system, which was constructed as a tri al system of desktop type, the temperature was precisely controlled. After the sensor system was optimized, a calibration curve was obtained with a de tection limit of 96 nM phosphate ion, a range between 96 nM and 32 mu M pho sphate ion, and a relative standard deviation of 2.3% (n = 5) at 25 degrees C. The sensitivity of this sensor was sufficient to determine the maximal permissible phosphate-ion concentration in the environmental waters of Japa n (0.32 mu M). In addition, the sensor could determine the calibration curv es between 0.16 and 32 mu M phosphate ion (five points, n = 3; averaged cor relation, r = 1.00) for at least 2 weeks, demonstrating enough stability fo r practical use. Furthermore, we investigated the influence on the sensor r esponse of dissolved substances in river water such as metal ions, heavy me tal ions, inorganic ions, and organic compounds. Treatment with activated c arbon could improve the response of the sensor when inhibited by dissolved substances in river water, except for manganese ion and uric acid. The sens or system could determine the concentrations of phosphate ion in various sa mples of river water from the Tone River. The results obtained by this sens or system and the modified molybdenum blue method were compared, and good c orrelation (r = 0.94) was obtained. (C) 1999 Elsevier Science B.V. All righ ts reserved.