John W. Dolan

After exploiting the chemical factors in the separation process, chromatographers can adjust column conditions – flow rate, column size, and particle diameter – to further improve separations.

In part III of this column series, John Dolan demonstrated that systematic variation of the solvent strength can change selectivity and retention, and changing solvent type can amplify the effect. This month, he looks at three additional parameters (pH, temperature, and column type) for adjusting selectivity.

Adapting the organic solvent strength and type can be an effective way to improve an isocratic separation.

Most chromatographers can look at a chromatogram and provide a qualitative opinion about the separation, but it is equally important to be able to measure the separation quality.

LC problems fall into one of two categories: those associated with instrumentation and those associated with the separation itself. Dolan explains how to identify which kind you have and how to approach correcting the problem.

Readers submit questions about how to isolate the source of carryover in LC methods, mobile-phase temperature effects, and the care of cleaning of columns.

Inadequate mobile-phase gassing may be the single largest cause of LC problems. Columnist Dolan examines bubble-problem sources and techniques that analysts can use to eliminate excess gas in the mobile phase.