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Frequently Asked Questions

Why does the chromatogram show split peaks?

Split Peaks can be caused by:

  • Column contamination
  • Partially plugged frit
  • Column Void
  • Injection Solvent Effects
  • Co-eluting compounds

Column contamination or partially clogged frits are generally caused when unfiltered samples are injected or when the sample solvent is different to the mobile phase. If the latter is the case, constituents of the sample may precipitate at the column inlet upon mixing with the mobile phase or by contact with the metallic surface of the frit.

A column void is formed either by hydrodynamic stress (high flow rate, high viscosity of the mobile phase) of a poorly packed column, by mechanical impact (the column was dropped on the floor) or by chemical dissolution of the packing material, e.g. pH > 12.

When using injection solvents that have higher elution strength than the mobile phase split or broader peaks can appear. The effect is most pronounced for early eluting peaks.

Split peaks can also occur by either two compounds that are almost co-eluting. If this is the case, the peaks should separate better if a column with higher efficiency (theoretical plates) is used. This can either be achieved by smaller particle size or a longer column. Also higher temperature and/or a less viscous mobile phase may promote a better separation.

Moreover, one compound can elute in two states, e.g. if not sufficient ion-pairing reagent is present in the mobile phase or the buffer capacity is deficient.