This article presents a method of simulating molecular transport in capillary gas chromatography (GC) applicable to isothermal, temperature-programmed, and thermal gradient conditions. The approach accounts for parameter differences that can occur across an analyte band including pressure, mobile phase velocity, temperature, and retention factor. The model was validated experimentally using a GC column comprised of microchannels in a stainless-steel plate capable of isothermal, temperature-programmed, and thermal gradient GC separations. The parameters governing retention and dispersion in the transport model were fitted with 12 experimental isothermal separations. The transport model was validated with experimental data for three analytes using four temperature-programmed and three thermal gradient GC separations. The simulated peaks (elution time and dispersion) give reasonable predictions of observed separations. The magnitudes of the maximum error between simulated peak elution time and experiment were 2.6 and 4.2% for temperature-programmed and thermal gradient GC, respectively. The magnitudes of the maximum error between the simulated peak width and experiment were 15.4 and 5.8% for temperature-programmed and thermal gradient GC, respectively. These relatively low errors give confidence that the model reflects the behavior of the transport processes and provides meaningful predictions for GC separations. This transport model allows for an evaluation of analyte separation characteristics of the analyte band at any position along the length of the GC column in addition to peak characteristics at the column exit. The transport model enables investigation of column conditions that influence separation behavior and opens exploration of optimal column design and heating conditions.

13This paper reports the first results of a robust, high performance, stainless-steel 14 microchip gas chromatography (GC) column that is capable of analyzing complex real 15 world mixtures as well as operating at very high temperatures. Using a serpentine 16 design, a 10 m column with an approximately semicircular cross section with a 52 µm 17 hydraulic diameter (Dh) was produced in a 17 cm x 6.3 cm x 0.1 cm rectangular steel 18 chip. The channels were produced using a multilayer chemical etch and diffusion 19 bonding process, and metal nuts were brazed onto the inlet and outlet ports allowing for 20 column interfacing with ferrules and fused silica capillary tubing. After deactivating the 21 metal surface, channels were statically coated with a layer of 0.16 µm (5%-phenyl)(1%-22 vinyl)-methylpolysiloxane (SE-54) stationary phase, and cross-linked with dicumyl 23 peroxide. By using n-tridecane (n-C13) as test analyte with a retention factor (k) of 5, a 24 total of 44,500 plates (≈4500 plates/m) was obtained isothermally at 120 °C. The 25 column was thermally stable to at least 350 °C, and rapid temperature programming (35 26 °C/min) was demonstrated for the boiling point range from n-C5 to n-C44 (ASTM D 2887 27 simulated distillation standard). The column was also tested for separation of two 28 complex mixtures: gasoline headspace and kerosene. These initial experiments 29 demonstrate that the planar stainless-steel column with proper interfacing can be a 30 viable alternative platform for portable, robust microchip GC that is capable of high 31 temperature operation for low volatility compound analysis. Since the introduction of silicon microchip gas chromatography (GC) columns by 34 Terry et al. (1) in 1979, there has been tremendous interest among researchers in 35 fabricating such columns in various substrates such as ceramics (2,3) glass (4), 36 polymers (5, 6) and metals (2, 7-9). Despite the wide variety of substrates employed, 37 silicon accounts for the majority at approximately 80% of all microchip GC columns 38 fabricated. The advantages of silicon include established micromachining technology, 39 capability of generating high aspect ratio features, cost effectiveness due to batch 40 processing, low thermal mass, high thermal conductivity, chemical inertness and 41 familiar silanol (Si-OH) chemistry to the popular fused-silica capillary column technology 42 (10). It is worth mentioning that although there are reports of all-silicon microcolumns 43 (both etched in and bonded with silicon wafers), in most cases, the channels are 44 microfabricated in a silicon substrate followed by anodically bonding to a Pyrex glass 45 top layer (1, 11,12). This design is not ideal as such silicon/glass hybrid systems exhibit 46 thermal expansion coefficient (CTE) mismatch (13), non-uniformity in temperature 47 91 column. After bonding the channels, stainless steel connection tubes were brazed to the 92 plate for connection to the inlet and detector. Unlike epoxy-based adhesives, since 93 brazing can handle high...