Carryover is observed in chromatographic systems when a previously injected analyte appears as a peak in the chromatogram of subsequent samples.
Carryover tends to occur when a small amount of analyte remains in the system after a sample is injected. You can measure carryover by observing analyte peaks that appear when you run a blank sample immediately after an analytical sample.
Waters specifies sample carryover on the Alliance iS System at 0.002% maximum.
A common cause of carryover is inadequate washing of the system, specifically the sample needle. Choosing an appropriate wash solvent can minimize carryover for a particular analysis (see Purge and wash solvent guidelines). The wash solvent must be strong enough to dissolve any remaining sample on the needle, and the wash duration must be long enough to remove the residue from the system.
Method conditions also affect carryover. Too short a hold-time at the final conditions of a gradient, especially if the gradient is steep, can fail to remove all analytes from the system or the column. It is important to completely flush the system and re-equilibrate the column before proceeding to a subsequent analysis.
When trying to minimize carryover, the hydrophobicity and solubility of samples as well as cleanliness during sample preparation are additional factors to consider, as is contamination from sample preparation tools.
Tip:
- Test your sample in the wash solvent to ensure that it does not cause either the analyte or the matrix to precipitate.
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