High-energy collision-induced dissociation tandem mass spectrometry of regioisomeric lactose palmitic acid monoesters using matrix-assisted laser desorption/ionization.

RATIONALE

Structural characterization and differentiation of three newly synthesized lactose monopalmitate regioisomers at positions O-3, O-3' and O-6' were realized by single-stage matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS) in the positive ion mode and by high-energy collision-induced dissociation tandem mass spectrometry (CID-MS/MS).

METHODS

A MALDI-TOF/TOF analyzer was utilized for the analysis of these isobaric lactose monopalmitate regioisomers. The CID-MS/MS spectra were acquired using high-energy cid with a 2 kV potential difference between the source acceleration voltage and the collision cell.

RESULTS

High-energy (CID) tandem mass spectrometry (MS/MS) analyses of the sodiated molecules, M + Na, showed distinguishing cross-ring product ions and characteristic fingerprint product ions, which allowed the straight-forward mass spectrometric characterization of these different regiosiomers.

CONCLUSIONS

This investigation allowed us to unravel the novel fragmentation behavior of the sodiated regioisoimer molecules obtained from the mono-substituted D-lactose fatty acid esters using high-energy CID-TOF/TOF-MS/MS analyses. The high-energy CID of the M + Na ions from the isobaric lactose monopalmitate regioiosmers promoted the formation of characteristic (0,2) A2 cross-ring cleavage product ions.