Kinetic potentiometric determination of creatinine in serum with a picrate ion-selective membrane electrode.

We describe a new kinetic method for potentiometric determination of creatinine in serum, based on the creatinine--picrate reaction in alkaline medium (Jaffé reaction). The reaction is monitored with a picrate-selective electrode, and the increase in electrode potential during 270 s is measured and related directly to the creatinine concentration. Small cation-exchange columns are used to separate creatinine from interfering substances. Analytical recovery of creatinine added to serum was 100.7%. Results for a series of samples compared well with results obtained with a spectrophotometric method (r = 0.994).