Measurement of urine porphyrins and porphyrinogens

A simple and rapid method for quantitative analysis of urine porphyrins is described. After acidification of urine to 1 n with HCl, the first derivative of the absorption spectrum is recorded in the region of the Soret band maximum. Nonspecific interference is not significant, and the point of intersection of the derivative of the Soret band maximum with the baseline provides an estimate of the ratio of uro- to coproporphyrins. Using this approach, which avoids solvent extraction prior to absorptiometry, we have defined pH-dependent differences in porphyrin and porphyrinogen partition between ethyl acetate and aqueous solvent or urine. These marked differences have been used to define conditions for separation of porphyrin and porphyrinogen prior to measurement. Using the methods described, recovery of uro- and coproporphyrinogens added to rat urine ranged from 87 to 100%.