Determination of hemoglobin through its peroxidase activity on chlorpromazine

Chlorpromazine is an excellent chromogen for determining micro-quantities of hemoglobin. The oxidation of chlorpromazine by peroxidase activity of hemoglobin is coupled to a non-enzymatic reaction of second-order. Kinetic analysis of the overall system leads to a discussion about the optimal assay conditions. Spectrophotometric progress curves for the accumulation of the chlorpromazine cation radical during the reaction have been obtained, and further analyzed by non-linear regression. The use of a linear calibration curve of the enzymatic reaction rate against hemoglobin concentration is proposed for its determination.