4.
Peaks with shoulders
There is no
specific measurement for the degree of a "shoulder" on a peak. In most
cases, the presence of a significant shoulder will increase the
measured tailing factor and/or decrease the
measured plate count. Characterization as a
shoulder, however, is a subjective judgment on the part of the
chromatographer.
If all the peaks
in the chromatogram have shoulders 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 have shoulders and the problem has gradually been
getting 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 have shoulders, 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 have shoulders 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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LC Resources, Inc. all rights reserved