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What is carryover in chromatography?
The short answer
Carryover is residue from a previous injection appearing in the next run, producing peaks that belong to another sample. It is controlled with blank runs between samples and by washing the injection path. Unmanaged, it can create phantom impurities in a clean sample or, worse, suggest a compound is present when it came from the vial before.
In detail
This is a real risk in a laboratory running many different peptides in sequence, which describes a third-party testing lab exactly.
The controls are routine and unglamorous: needle washes, blank injections at defined intervals, and acceptance criteria for what a blank may show before the sequence is invalidated.
A laboratory that publishes its method lets you see whether those controls exist. One that describes its process only in general terms is asking you to assume they do.
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