Steps for Ensuring Good Column Performance

Step 4: Quickly Determine When a Column is Going Bad

Eventually all columns lose performance and must be replaced. Timing depends on the chromatographic conditions used as well as the column itself. By monitoring column performance you can tell when your column is starting to "wear out" and predict how often your columns will need to be replaced. Also by understanding the major factors that limit column lifetime, steps can be taken to extend the usable lifetime of a column. The important column parameters to monitor are theoretical plates (N), capacity factor (k), selectivity (), tailing factor (T_f), and back pressure. Many data systems allow these parameters to be printed as a part of the chromatographic report, simplifying the job of monitoring column performance.

Parameter		What to Look For
Theoretical plates, N (efficiency)		Theoretical plates is a measure of the efficiency, or resolving power, of a column. The most common reasons for losing theoretical plates are column voiding and column fouling. Peaks in your chromatogram broaden with decreasing efficiency. By monitoring N, you can detect these problems long before they affect your chromatographic separation.
Capacity factor, k		Capacity factor is a measure of retention independent of flow rate and column dimension. Changes in capacity factor under constant chromatographic conditions may indicate either problems with loss of bonded phase or problems with column fouling due to non-eluting compounds. However, changes in capacity factor may also be caused by changes in mobile phase composition that give the false impression of a column problem.
Selectivity,		Selectivity is a measure of the relative retention of two compounds. Shifts in selectivity are an additional indication, along with capacity factor, of problems with loss of bonded phase, column fouling, or changes in mobile-phase conditions.
Tailing factor, Tf		Tailing factor is a measurement of peak symmetry. An increase in the tailing factor may indicate a problem with column voiding but may also result from an interaction between polar solutes and silanol sites, permitted by the loss of bonded phase.
Column back pressure, P		If column back pressure increases, it is almost always due to particulates that have collected on the column inlet frit. However, column voiding induced by column packing collapse can cause a large surge in pressure. Monitoring these HPLC parameters helps you decide when it is time to replace your column.

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