Doubly charged porphyrin ion tandem mass spectrometry: Implications for structure elucidation

Abstract

Under electron ionization (EI) conditions, porphyrins yield unusually high intensities of doubly charged molecular and fragment ions. These doubly charged ions offer unique opportunities for the structure elucidation of porphyrins by tandem mass spectrometry (MS/MS). First, they fragment to a greater extent than the corresponding singly charged ions under both EI/MS and EI/MS/MS conditions. Second, doubly and singly charged porphyrin ions often fragment via different pathways, and can therefore yield different structural information. This paper describes several ways in which analyses of doubly charged porphyrin ions with a triple quadrupole tandem mass spectrometer can be useful in structure elucidation of porphyrins. The effect of the metal atom on the fragmentation of metalloporphyrins in an EI source is demonstrated by correlating the extent of doubly charged fragment ion formation to a stability index. Doubly charged porphyrin ions are shown to yield predominantly doubly charged daughter ions upon collisionally activated dissociation (CAD), and are also shown to fragment to a greater extent than corresponding singly charged porphyrin ions. Advantages and disadvantages of doubly charged porphyrin ion MS/MS for structure elucidation are discussed.

Comprehensive analysis of metalloporphyrins via high irradiance laser ionization time-of-flight mass spectrometry

“…Several mass spectrometric techniques, such as chemical ionization, 5 electron ionization, 6 MALDI-, 7 ESI-, [8][9][10] and secondary ion (SI-) MS, 11,12 have been used to analyze porphyrins and their metal complexes. Many of these compounds, however, are practically insoluble in water or general organic solvents other than toxic solvents.…”

“…16,17 LI-TOFMS may also be considered for analysis of organic compounds, as this technique was used to successfully characterize benzoylferrocene. 18 In this report, we focus on an LI-TOFMS analytical strategy, different from those methods mentioned, [5][6][7][8][9][10] for the analysis of metalloporphyrins. Comprehensive information on metallic/nonmetallic elements, characteristic fragments, and intact molecules of analytes can be selectively acquired through the variation of helium buffer gas pressure in the ion source.…”

MALDI‐TOF mass spectrometric analysis for the characterization of the 5,10,15,20‐tetrakis‐ (m‐hydroxyphenyl)bacteriochlorin (m‐THPBC) photoproducts in biological environment

“…Porphyrin‐like compounds have been extensively studied in the past by mass spectrometry coupled with electron ionization (EI),6 chemical ionization (CI),7 fast atom bombardment (FAB),8 plasma desorption,9 laser desorption10, electrospray (ESI)11 and matrix assisted laser desorption (MALDI) 12, 13. Among these ionization techniques, MALDI appears to be one of the most attractive and allows the analysis of complex media with salts and proteins.…”

Travelling wave ion mobility mass spectrometry of 5‐aminolaevulinic acid, porphobilinogen and porphyrins

“…The drift times of the singly and doubly charged porphyrins are summarised in Table and their m/z value are shown in Table . Doubly charged porphyrin ions have previously been studied by electron ionisation (EI)‐MS, fast atom bombardment (FAB)‐MS and matrix‐assisted laser desorption/ionisation (MALDI)‐MS . Doubly charged synthetic glycoporphyrins have also been studied by ESI‐MS/MS; however, they have not been described in HPLC/ESI‐MS nor in IMS‐MS analysis.…”