5.
Split peaks
Peak "splitting"
is not characterized by any particular measurement; it is a subjective
evaluation on the part of the chromatographer. Split peaks can
generally be regarded as simply well-resolved shoulders. The causes and
diagnostics follow similar rules.
If all the peaks
in the chromatogram are split, and the problem appeared suddenly,
then the following possibilities should be checked:
1. A
partially-plugged frit at the column inlet.
2. A
head space or void at the column inlet.
3. Incorrectly
prepared mobile phase (pay special attention to buffer concentration
and pH).
4. A
dilution solvent that is stronger than the mobile phase.
If all the peaks
in the chromatogram are split and the problem has been getting
gradually worse, then the following possibilities should be checked:
1.
A head space or void at the column inlet.
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 chromatograms are split, while other peaks look
normal, and the problem appeared suddenly, 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. A partially-resolved
interference.
If only some of
the peaks are split and the problem has gradually been getting worse,
then the most likely cause is chemical contamination or
attack on the stationary phase. In most cases, the most
cost-effective solution is simply to replace the column.
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