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8. Extra peaks
"Extra" peaks are usually real; they represent actual components separated by your chromatography system.

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 include:
  • the water system
  • buffers/salts/additives
  • dirty glassware
  • contaminated pH electrodes, etc.
  • Column or instrument hardware.

  • Prevention is the best approach, but residual contamination can be reduced in a number of ways:

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