Imaging Analysis of Amino Acids and Sugar using a Dielectric Barrier Discharge Ionisation-Mass Spectrometer coupled with Laser Ablation Sampling Technique

Abstract

Distribution and concentration of certain organic compounds in drugs or biological tissue samples can provide key information to understand the behaviour and effect of that chemical species. In this study, we developed an analytical technique to perform mass spectrometry imaging for organic compounds under atmospheric pressure. The laser ablation technique was used as a sample introduction method to ablate a small amount of sample by focusing laser light onto the sample surface. Laser-induced sample particles were transferred by an argon gas stream to a newly developed plasma-based ion source for ionisation. The capability of this analytical method was demonstrated with the analysis of amino acids. Either protonated ([M+H]⁺) or ammoniated ([M+NH₄]⁺) ions, with slight fragments, were observed for the amino acids and sugar, suggesting a fairly soft ionisation was achieved. Analytical repeatability defined by nine times repeated analysis was better than 10%. More importantly, linear correlations between the signal intensities and concentration of analytes were obtained for three amino acids (valine, methionine, and phenylalanine). With the present analytical technique, imaging analysis of several amino acids and sugar was carried out with a tablet sample. The resulting imaging can be used to evaluate the homogeneity of drug components both the within and among the tablets.

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