HPLC Products

Problem

By Ghost Peaks, we refer to peaks which appear in the chromatogram, but do not originate from the sample.

Under isocratic conditions, there really should not be any ghost peaks. If you leave the system running long enough all peaks should come out and nothing further will happen until the next injection is made. There are two likely causes for ghost peaks under isocratic conditions:

Late running peak from a previous chromatogram

This could arise because the run time is too short, or a second injection was made without waiting for the previous run to finish. Occasionally an extra peak or two can result from a double injection (eg the valve is turned for flushing while the run is still happening, and material is flushed onto the column.

This can also be observed if the system has not been allowed to reach dynamic equilibrium, or if a solvent change has been made.

Contamination.

Injection valve may not be clean, or material not washed from loop can be eluted with a sample injection

The top bead of the column can contain material which has fallen out of solution after a previous injection. This could be because the injection solvent was not a good enough solvent, or the concentration was too high, or the sample was not sufficiently miscible or soluble in the eluent. This can occur especially if a solvent change to a stronger eluent is made.