Quantitative determination of erythrocyte zinc protoporphyrin

An elevated zinc protoporphyrin (ZPP) level in blood is indicative of lead poisoning (as well as iron-deficiency anemia) and is the basis for certain fluorometric screening tests. The calibration of such test protocols and instruments requires ways to reliably determine absolute ZPP concentrations in blood. Two such methods are described: one is an ethanol extraction method and the other a fluorometric addition method using detergent hemolyzed blood. A careful determination of the molar extinction coefficient of ZPP gives EmM=161 in pyridine. Corrections are offered for a previously published protocol for determining the ZPP concentration from the fluorescence intensity of diluted blood. The choice of units for expressing the ZPP concentration in blood is discussed, as is the absorbance correction in quantitative fluorometry of samples which are not optically thin at the excitation wavelength.