Gas chromatography open columns

In GC we have a real choice between packed columns (dp = 100-200 pm 150-65 mesh) and open columns (dc= 50-500 pm). Capillary columns have the advantage of enhanced speed of analysis (eqn.7.6). In order to exploit this advantage, narrow-bore capillaries (dp 100 pm) should ideally be used. However, such columns require relatively high inlet pressures (especially for high plate counts) and considerable experimental modifications and have a very low sample capacity [702], 

Because of all these reasons, so-called wide-bore capillaries (dc 500 pm) have recently gained considerable popularity. These columns, which are usually provided with a thick (about 1 pm) film of stationary phase, behave in a fairly similar way to packed columns. They show low pressure drops (allowing them to provide a much higher efficiency than packed columns), may easily be installed in most instruments and have a high sample capacity. However, they also behave similar to packed columns in terms of separation speed. Therefore, the current capillary columns with diameters between 100 and 300 pm form a reasonable compromise between instrumental limitations and theoretical promises. 

Despite the current popularity of wide-bore capillary columns, it is to be expected that advances in instrumentation and column technology, combined with the increased 

Packed columns may still be used in GC as a robust tool to effectuate simple, routine separations. They have two fundamental disadvantages relative to capillary columns  

limited efficiency due to a high pressure drop per unit length. 

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