Column Length Selection Summary 1. Start with 25-30 meter columns when the best length is unknown. 10-15 meter columns are well suited for samples containing very well separated solutes or very few solutes. Shorter lengths are used for very small diameter columns to reduce head pressures. Best suited for complex samples containing a large number of solutes.
Long columns have long analysis times and higher cost.
For isothermal conditions, solute retention is directly proportional to film thickness. Thicker film columns are used to obtain higher retention for very volatile solutes. Changing to a thicker film column has a net effect of providing equal or greater retention at a higher column temperature. Thicker film columns are typically used for volatile compounds like solvents and select gases. Thinner film columns are used to reduce the retention of highly retained solutes.