Diagnostic:
Sample overload
Flat-top peaks are often caused by
sample loads that exceed the linear range of the detector. Dilute the
sample by a factor of 10 and re-inject.
Tailing peaks are often caused by
sample loads that exceed the capacity of the column. As the stationary
phase surface becomes saturated with analyte molecules, the excess
sample tends to stay in the mobile phase and elute more quickly. The
result is that the top (high concentration) part of the peak moves
faster than the leading edge (low concentration) of the peak. Dilute
the sample by a factor of 10 (adjust detector range as necessary) and
re-inject. If the peak shape improves and the retention time (for the
top of the peak) increases, the overload is confirmed.
Fronting peaks are often caused by
sample loads which either exceed the buffer capacity of the mobile
phase or which exceed the solubility of the analyte. The excess sample
tends to stick to the stationary phase. The result is that the top
(high concentration) part of the peak moves more slowly than the
trailing (low concentration) edge of the peak. Dilute the sample by a
factor of 10 (adjust detector range as necessary) and re-inject. If the
peak shape improves and the retention time (for the top of the peak)
decreases, the overload is confirmed. If the analyte is ionizable (weak
acid or base), check the pH and buffer concentration of the mobile
phase.
Ref: LC-GC
16(5)
442 (1998)
Ref: LC-GC
17(6)
508 (1999)
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LC Resources, Inc. all rights reserved