On-line LC-MS analysis of urinary porphyrins

A reversed-phase high-performance liquid chromatograph-v-mass spectrometry (LC-MS) method is described for the separation and simultaneous analysis of porphyrins related to disorders of heme biosynthesis (uro-, heptacarboxylic, hexacarboxylic, pentacarboxylic, and co-proporphyrins). The method involves initial porphyrin esterification and extraction from urine, Detection and quantification is performed from the extracts by separation with a Hypersil BDS column and on-line detection by MS through coupling with an atmospheric pressure chemical ionization interface. The porphyrin esters are detected as protonated molecules [M + H](+). Their mass spectra also exhibit an [M + Na](+) fragment of lower intensity. The analytical performance of this method is compared with those of LC with UV and fluorescence detection. LC-MS used in selective [M + H](+) ion monitoring provides the lowest detection and quantitation limits. Zn scan mode, this LC-MS method affords, without further isolation or concentration steps, the measurement of mass spectra of unknown compounds present in the urine of patients with altered porphyrin excretion.