Microfabricated Gas Chromatography Columns With Monolayer-Protected Gold Stationary Phases

This paper reports the first microelectromechanical-systems (MEMS)-based stationary phase coating technique called monolayer-protected gold for ultranarrow single-capillary (SCC) and multicapillary (MCC) microfabricated gas chromatography (??GC) columns, yielding the highest separation performance reported to date. The conventional coating methods are mainly based on the solvent evaporation of a polymeric solution. These methods, which are developed for fused silica capillary tubing, cannot afford conformal coating in the rectangular-shaped ??GC columns with high-aspect-ratio structures. The proposed wafer-level coating technique overcomes this traditional challenge by merging MEMS and nanotechnology. This new ?? GC stationary phase is achieved by electrodepositing a uniform functionalized gold layer with an adjustable thickness (250 nm-2 ??m) in 25-??m-wide SCCs as well as in four-capillary MCCs. The electrodeposition process is optimized to achieve uniform and conformal coverage in high-aspect-ratio ??GC columns. In order to predict the optimized electroplating conditions for different column dimensions, the theoretical model based on the experimental results is developed and introduced in this paper. The separation performance, stability, reproducibility, and bleeding of the stationary phase are evaluated over time by separating n-alkanes as nonpolar and alcohols as polar gas mixtures.