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2. Tailing or fronting peaks
Peak tailing is measured either by the tailing factor or the asymmetry factor. Most chromatographic peaks tail (TF > 1)to some extent; the allowable degree of tailing is usually stated in the system suitability criteria. Fronting (TF < 1) is less common.

If all the peaks in the chromatogram tail excessively, and the tailing problem appeared suddenly, then the following possibilities should be checked:
  1. A partially plugged frit at the column inlet.
  2. (gradient separations only) Excessive extra-column volume.
  3. A head space or void at the column inlet.
  4. Incorrectly prepared mobile phase (pay special attention to buffer concentration and pH).
  5. A dilution solvent that is stronger than the mobile phase.

If all of the peaks in the chromatogram tail excessively, but the problem has been gradually worsening, then the following possibilities should be checked:
  1. 1. A head space or void at the column inlet.
  2. 2. Chemical contamination or attack on the stationary phase. In most cases, the most cost-effective solution is simply to replace the column.

If only some of the peaks in the chromatogram tail excessively, while other peaks appear normal, then the following possibilities should be checked:

1. A dilution solvent that is stronger than the mobile phase.

2. Incorrectly prepared mobile phase (pay special attention to buffer concentration and pH)

3. (isocratic separations only) Check for extra-column volume (especially if early peaks tail more than later peaks).

4. Chemical contamination or attack on the stationary phase. In most cases, the most cost-effective solution is simply to replace the column.

5. Sample overload.

Ref: LC-GC, 15(1) 24 (1997)
 Ref: LC-GC, 15(11) 1018 (1997)



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