Direct Quantitative Analysis from Thin-Layer Chromatography Plates Using Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry

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Abstract
Direct quantitative analysis using thin-layer chromatography (TLC) coupled with matrix-assisted laser desorption/ionization mass spectrometry (MALDI) has been demonstrated. An internal standard and a data collection protocol were used for analysis directly from TLC plates to compensate for shot-to-shot signal degradation, as well as deviations of analyte and internal standard spatial distributions within the TLC spot. Cocaine hydrochloride was used as a model compound for this study, and cocaine- d3 was used as the internal standard. Quantitative analysis by TLC/MALDI yielded comparable results to those obtained with stainless steel substrates (the standard MALDI method) for point-to-point repeatability, % RSD of the standard curve, and measurement precision. For silica gel and reverse-phase TLC plates, the relative standard deviation of the standard curve slope was better than 3%, the relative standard deviations of the analyte/internal standard intensity ratios ranged from 3.8% to 9.5%, the precision was estimated to be better than 12%, and the detection limits were estimated to be 60 pg for both TLC plate types. Quantitative analysis using stainless steel substrates yielded a lower detection limit than that obtained by TLC/MALDI by a factor of six. Perspectives for improving the detection limits of direct TLC/MALDI quantitative analysis are discussed. Index Headings: MALDI; TLC; Quantification.