Structure elucidation of geoporphyrins by desorption tandem mass spectrometry: carbon-number, pyrrolic structure, and sequencing information from one experiment
Conference
Beato, BD, Yost, RA, Quirke, JME. (1989). Structure elucidation of geoporphyrins by desorption tandem mass spectrometry: carbon-number, pyrrolic structure, and sequencing information from one experiment
. 34(1), 184.
Beato, BD, Yost, RA, Quirke, JME. (1989). Structure elucidation of geoporphyrins by desorption tandem mass spectrometry: carbon-number, pyrrolic structure, and sequencing information from one experiment
. 34(1), 184.
Tandem mass spectrometry (MS/MS) is a valuable tool in the structure elucidation of geoporphyrias. However, separate MS/MS experiments with a variety of ionization techniques (EI, PCI, and NCI) are usually required to determine carbon-number distribution, identify peripheral substituents and sequence the pyrroles. We have developed an MS/MS technique in which all three types of information are obtainable in a single experiment. The sample is introduced on the filament of a temperature programmable direct exposure probe (DEP) under hydrogen (H2CI) conditions into a triple quadrupole mass spectrometer. As the filament heats up, the porphyrins vaporize, either to be ionized in the H2 plasma, or to recondense on cooler surfaces within the ion source. The positive molecular ions which form are selected to undergo collisionally activated dissociation (CAD) with Ar, resulting in cleavage of peripheral substituents, to permit their identification. Negative molecular ions may also be monitored simultaneously to provide carbon-number information, as they do not fragment appreciably under these conditions. Once all of the sample has vaporized off of the DEP filament, the Ar is turned off and the instrument is switched under data system control to scan for only positive ions. As the DEP filament continues heating to temperatures exceeding 1300°C, other surfaces within the ion source heat up, causing surface-induced decomposition of the recondensed porphyrins followed by vaporization and chemical ionization of the decomposition products to form mono- and di-pyrrolic ions. The applications of this technique to the characterization of porphyrins will be discussed.
