Detection of Amino Acids, Peptides and Antibiotics by Laser Desorption Postionization Mass Spectrometry

Mass spectrometry plays an important role in analysis and identification of a wide variety of compounds. Laser desorption postionization (LDPI) is an emerging mass spectrometric (MS) technique that is showing significant promise to improve both the sensitivity and selectivity of analysis. This thesis mostly explored LDPI-MS using single photon ionization for selective detection with 7.87 eV photon energies, but some work is reported with 10.5 eV photon energies. Molecules not detectable by 7.87 eV LDPI-MS may be tagged with a chromophore to allow detection, allowing additional mode of control as the tag may be made chemically selective for different classes of molecules. Pyrenyl maleimide, piperazine and dansyl chloride are shown as tags for selective detection of peptides by LDPI-MS. Pyrenyl maleimide is a cysteine selective tag that was reacted with a trypsin digest of bovine serum albumin protein and lead to the detection of a large number cysteine containing peptides by LDPI-MS. Piperazine and dansyl chloride bind to primary and secondary amines and have the potential to allow detection of species that may not have been previously possible. Tagging was also applied to the intact bacterial biofilm that was previously spiked with known peptides. This allowed for the detection of these peptides within the biofilm without any need for extraction. Modification and tagging was also applied to antibiotics. Ampicillin is an antibiotic that could not be efficiently detected by LDPI-MS. Addition of the piperazine tag allowed for the stabilization of the charge. After tagging, the new molecule was tested to ensure that its potency as an antibiotic still remained.