discuss the use of capillary columns gas chromatograph analysis?

Answer 1

Gas chromatography columns are of two designs: packed or capillary. Packed columns are typically a glass or stainless steel coil (typically 1-5 m total length and 5 mm inner diameter) that is filled with the stationary phase, or a packing coated with the stationary phase. Capillary columns are a thin fused-silica (purified silicate glass) capillary (typically 10-100 m in length and 250 µm inner diameter) that has the stationary phase coated on the inner surface. Capillary columns provide much higher separation efficiency than packed columns but are more easily overloaded by too much sample.
Capillary columns have a very small internal diameter, on the order of a few tenths of millimeters, and lengths between 25-60 meters are common. The inner column walls are coated with the active materials (WCOT columns), some columns are quasi solid filled with many parallel micropores (PLOT columns). Most capillary columns are made of fused-silica with a polyimide outer coating. These columns are flexible, so a very long column can be wound into a small coil.
Some analysts do not have the freedom to choose a different type of column because their analytical methods dictate one specific column. Other analysts may keep using the same column because it works, even though it may not be the best choice for their samples. But, how was the current column chosen? Was the column choice determined by careful investigation of all column parameters and subsequent optimization for the specific application? Or, was the column chosen because it happened to be installed in the GC during method development?
When purchasing a new column, the most important consideration is the stationary phase. There are many different interactions that occur between the analytes and the functional groups of the stationary phase. These interactions contribute more to the overall results of the analysis than any other factor in the column. That is why it is important to understand as much about your column and sample as possible.