Reactivity of acetoacetate with alkaline picrate: an interference of the Jaffé reaction

Spectrophotometric, kinetic, and polarographic studies of the interaction of acetoacetate with alkaline picrate have been undertaken in the presence of aqueous NaOH concentrations ranging between 0.50 mol/L and 2.50 mol/L. Spectrophotometric data has substantiated formation of the following acetoacetate-picrate complexes: 1:1 red, 490 nm; 2:1 orange, 390 nm; and 3:1 colorless, 265 nm. Depending upon the time of measurement, the composition of alkaline picrate, and the acetoacetate level in the test samples, acetoacetate may be either a positive or negative interference in kinetic Jaffé methods for the determination of creatinine. Polarograms of alkaline picrate in 0.50 mol/L NaOH showed three well-defined nitro group reduction waves and a more diffuse fourth reduction wave with approximate half-wave potentials of -0.62 V, -0.79 V, -0.94 V, and -1.32 V, respectively. Increasing the concentration of hydroxide and/or acetoacetate resulted in the disappearance of reduction waves 1 to 3 with only reduction wave 4 remaining. Based upon the polarographic results, a trinitro anion structure has been assigned for the 2:1 acetoacetate-picrate complex.