Development of a Sol-Gel-Based Thin-Layer Chromatography Stationary Phase for in-situ Infrared Analysis

Abstract

A sol-gel stationary phase was developed for in-situ infrared (IR) detection of analytes on thin-layer chromatography (TLC) plates. These sol-gel-based TLC plates have improved optical properties compared with conventional TLC plates in IR spectroscopic analysis. Samples can be analyzed in transmission geometry, requiring no special attachments. The sol-gel-based TLC plates demonstrate significantly better light throughput and a wider spectral range than conventional TLC plates analyzed in diffuse reflectance geometries.The sol-gel precursor, methyltrimethoxyorthosilicate (MTES), was templated with cetyltrimethylammonium bromide (CTAB) and urea in order to form a porous sol-gel. Aerosol deposition was used to apply the sol-gel solution onto either glass slides or silicon wafers within an enclosed chamber. Many variables were studied to determine their effect on the quality of the sol-gel stationary phases, including the ratio of MTES:methanol:water:CTAB:urea:HCl:, gelation times and temperatures, and deposition rate. Sol-gel films prepared using MTES/methanol/water/CTAB at ratios of 1 : 20 : 7 : 0.2 containing 5 wt% urea (relative to MTES) and pH 1.5 were crack-free, mechanically stable, and uniform in appearance. The films were tens of microns thick with a highly interconnected porous structure.For chromatographic separations, the films exhibited good solvent migration velocity and could be repeatedly washed and reused for TLC separations without showing degradation in the separation. Several different classes of compounds, including polyaromatic hydrocarbons and dyes, were successfully separated. Theoretical plate values measured on the MTES-based sol-gel films were comparable to those obtained on commercially available TLC plates.