Use of p-methoxy cinnamaldehyde in label-assisted laser desorption/ionization mass spectrometry (LALDI-MS) for detection of different classes of primary amines, amino acids and neurotransmitters

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), useful for the detection of macromolecules, is generally not suitable for recording the mass spectrum of small molecules, especially within the range of m/z 500, because of the appearance of matrix cluster peaks in the small molecular weight range. To circumvent this problem, a matrix-free variant of MALDI-MS, namely Label-assisted laser desorption/ionization mass spectrometry (LALDI-MS) has been developed in recent years where analytes get covalently attached to a laser absorbing label which induces the desorption/ionization process thus facilitating the recording the mass spectra and avoiding the problem of formation of cluster peaks. In general, the probes used for such detections are all pyrene-based scaffolds which despite being a good laser-active chromophore have both reactivity and solubility problems. Inspired by the right chromophoric nature, we have undertaken a systematic study to design and optimize cinnamaldehyde derivatives and have found that p-methoxy cinnamaldehyde (PMC) as a simpler, cost-effective, less hydrophobic laser-active label, which can detect a series of primary amines, including the neurotransmitters and amino acids. The label PMC can also discriminate between aliphatic and aromatic primary amines.