are usually real; they represent actual components separated by your
If your standard
solutions show the correct number of peaks, but your samples have extra
peaks, the most likely explanation is contamination of the sample. In
general such peaks will be comparable in width to the peaks around them.
A less likely
problem is the occurrence of late eluters from an earlier
injection. In general, such late-eluting peaks will be significantly
wider than the peaks around them.
In the case of
gradient separations, extra peaks that show up in standards, samples,
and blank gradients are usually caused by contamination of the weak
solvent. This can be confirmed by running a series of blank
gradients with increasing equilibration times between gradients. If the heights/areas of
the extra peaks increase with increasing equilibration time, this
confirms weak solvent contamination as the cause. Possible sources
the water system
or instrument hardware.
is the best approach, but residual contamination can be reduced in a
number of ways:
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