FLUOROMETRIC-DETERMINATION OF POTASSIUM-ION USING HEXADECYL-ACRIDINE ORANGE IMMOBILIZED ON A POLY(VINYL CHLORIDE) MEMBRANE ATTACHED TO A FLOW-THROUGH CELL

A cationic fluorescent probe of hexadecyl-acridine orange is immobilized on a poly(vinyl chloride) membrane containing valinomycin. The membrane is attached to the inner wall of the flow-through cell in a fluorescence spectrometer, and potassium ion is detected repetitively by a flow injection system without consuming the indicator reagent. The response is proportional to the logarithmic concentration of the potassium ion in the range 0.5 - 50 mM. Fifteen samples are determined in 1 h, and the relative standard deviation of the peak height is 2.4% for a sample containing 0.1-mu-mol (1 mM) of potassium ion. The extended Nicolsky equation is applied to the observed peak height, the selectivity coefficient for sodium ion being 4 x 10(-3). The concentration of potassium ion in human blood plasma is also determined by this system.