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

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.

Theory and Practice of UHPLC and UHPLC–MS

“…This combination of pores was not completely new, because the significant effect of similar morphologies has long been recognized in studies concerning heterogeneous catalysts. Nir and Pismen (1977) were probably the first who discovered the enhancement of catalyst effectiveness by convection. Rodrigues et al (1992Rodrigues et al ( , 1993 quantified the concept of augmented diffusivity by forced convective flow due to a pressure gradient, and their studies became the key to understanding perfusion chromatography.…”

“…Because both TLC and MALDI MS operate with 2D devices/plates, MALDI MS prevailed in direct coupling with TLC. In the mid-1990s, Gusev et al published first demonstration of separations of proteins and peptides using TLC on plain silica layers with MALDI MS detection followed by a series of more specific papers (Gusev et al, 2000(Gusev et al, , 1995aMehl et al, 1997;Nicola et al, 1996;Vermillion-Salsbury et al, 1999). In addition to successful separation and detection, they also found that the detection limit was several orders of magnitude lower than that typical of conventional MALDI and even lower than "classical" UV detection (Gusev et al, 2000).…”

“…Detection to visualize the results of the separation in 2D TLC is also important. Although the "classical" detection methods such as staining or labeling provide information related to the position of the spot and retardation factor, MS adds another dimension to the separation by identifying the isotopic mass of the separated compounds (Nurok et al, 1987). A desired sensitivity boost was ascribed to the introduction of the desorption electrospray ionization (DESI) interface (Cooks et al, 2006;Takats et al, 2004Takats et al, , 2005) that can be operated in scanning mode (Ifa et al, 2007;Wiseman et al, 2006).…”

Quantitative analysis of technical polymer mixtures by matrix assisted laser desorption/ionization time of flight mass spectrometry

“…The principal activity in this area has been reported by Nelson et al [1] as well as by Hercules et al [2][3][4][5][6]. In their studies, proteins and peptides were analyzed and the intensities of single peaks were considered.…”

“…The limit of detection (LOD) was 7 ng/ml and 10 ng/ml for TOF-SIMS and MALDI, respectively. Hercules et al studied the direct coupling of thin-layer chromatography (TLC) with MALDI for the analysis of a cocaine hydrochloride, using cocaine-d 3 as an internal standard [3]. Their rationale for combining TLC with MALDI was based upon TLC being used as a standard method for the analysis of drugs of abuse, while cocaine-d 3 is available as an internal standard, and that quantitative analysis of cocaine by MALDI had been previously demonstrated [4].…”