Compensation by zinc chelation for fluorescent background in determining coproporphyrin and uroporphyrin in urine.

An improved method for separation and fluorescent analysis of coproporphyrin and uroporphyrin in urine was presented by Sobel, Cano, and Thiers [Clin. Chem. 20, 1397 (1974)]. Accurate determination of porphyrin concentrations by this method is impeded by the fluorescent background in urine samples, which varies from one specimen to another. By use of a straightforward procedure, zinc may be incorporated into coproporphyrin and uroporphyrin. Measurement of the difference in the fluorescent emission intensity at 650 nm for the porphyrin solutions before and after zinc incorporation compensates for fluorescent background and gives a more accurate determination.