High-performance liquid chromatography of naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers.

Naturally occurring 8-, 7-, 6-, 5- and 4-carboxylic porphyrin isomers are separated on C18 reversed-phase columns with various proportions (13-31%, v/v) of acetonitrile in 1 M ammonium acetate buffer (pH 5.16) as the mobile phases. Hydrophobic interaction between the porphyrin side chain substituents and the C18 hydrophobic surface is the main retention mechanism. Ion-exchange behaviour is also observed, but this does not influence the relative retention of the isomers. All possible forms of the decarboxylation intermediates of uroporphyrinogen III are detected in normal and porphyric urine, and the results provide conclusive evidence for the existence of decarboxylation pathways other than the currently accepted clockwise sequence, starting at the ring D acetic acid group of uroporphyrinogen III.