Problem Set I V – Gas Chromatography 1. (a) packed columns offer high sample capacity, while open tubular columns give better separation efficiency (smaller plate height), shorter analysis time, and increased sensitivity to small quantities of analytes. (b) Wall-coated: liquid stationary phase bonded to the wall of column Support-coated: liquid stationary phase on solid support on wall of column Porous layer: solid stationary phase on wall of column 2. (a) Open tubular columns eliminate the multiple flow path term (A) in the van Deemter equation, decreasing plate height. Also, the lower resistance to gas flow allows longer columns to be used with the same elution time. (b) Diffusion in H 2 and He is more rapid than in N 2 . Therefore, equilibration of solute between the mobile phase and the stationary phase is faster. 3. (a) Split injection is the ordinary mode for open tubular columns. It is best for high concentrations of analyte, gas analysis, high resolution, and dirty samples (with an adsorbent packing in the injection liner). Splitless
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