Potentiometric and optical measurements for the determination of ephedrine

A PVC membrane electrode based on the ephedrine reineckate ion pair was constructed. Small ion pair percentages (0.1-5\% w/w) were tested successfully giving Nernstian behavior. The slope of the calibration graph was 56 mV/decade for the 5\% ion pair. The optimum working pH range of the electrode is 4.0-9.0. The linear usable concentration range is 2 x 10(-6) to 10(-1) M ephedrine. The suitable selectivity of the electrode toward ephedrine relative to other cations, amines, sugars, and some pharmaceuticals was recorded. The potential drift of the electrode did not exceed 0.58 mV/day. The effect of temperature on electrode performance was studied in the range of 25-95 degrees C and it worked with Nernstian behavior up to 85 degrees C. Electrode performance is compared with that of previously reported electrodes. The determination of ephedrine in its pharmaceutical preparations was performed with a mean recovery of 98.7\% and average relative standard deviation of 1.9\%. Application of the membrane to optical measurements for ephedrine was attempted at different pH values. (C) 1998 Academic Press.