Question

Capacity factor – why it is used instead of retention time

Answer 1

Capacity factor is an indication of how long a compound can be retained by the stationary phase. It is calculated as, k = (Tr - To)/To, where Tr is the retention time of the target and To is the unretained peak time. If Tr = To, then the sample is not retained by the stationary phase. Higher the value for k, longer the retention.

The retention time for a compound is not fixed as many factors can influence it even if the same GC and column are used. These include:

• The gas flow rate
• Temperature differences in the oven and column
• Column degradation
• Column length

This is the reason why capacity factor is used instead of retention time.