Isotachophoretic analysis of the lipophilic cation tetraphenylphosphoniumbromide

Abstract

Tetraphenylphosphoniumbromide (TPP), a lipophilic cation used for the determination of plasma membrane potential, was quantified by isotachophoresis. The optimized leading electrolyte consisted of 10 mmol/l KOH as leading ion, supplemented with 0.5% hydroxy-ethylcellulose. The pH was adjusted to 9.5 with methionine. The terminating ion was 10 mmol/l tris(hydroxymethyl)-aminomethane (pH 9.2, adjusted with methionine). Leading ion concentrations of 10, 1 and 0.5 mmol/l respectively, showed nearly the same detection limits (2×10−11 mol of TPP). This detection limit allowed the quantitative determination of TPP down to a concentration of 2 μmol/l. Calibration curves in the range of 2×10−11 to 1.5×10−10 mol of TPP showed correlation coefficients greater than 0.95 (n=12; α=0.01).