Reducing carryover

Failure to follow specified guidelines can lead to unwanted carryover between injections.

In a chromatographic system, any substance that creates unwanted peaks or excessive background noise is contamination. Carryover, a specific type of contamination, occurs when sample material remaining in the system after an injection appears as peaks in subsequent injections, compromising quantification. To optimize system performance, carryover must be minimized and held to an acceptable level (often below the limits of detection).

Carryover can result from incorrectly installed tubing, fittings, or other hardware or by ineffective wash solvents. Take these actions to reduce carryover:

• Restrict extension loop usage to one system.
• Ensure that all tubing connections are properly seated. Before tightening the fitting compression screws, tubing must seat properly (without internal gaps) inside all connection ports. Poorly seated connections create reservoirs of unnecessary space that retain sample, increasing carryover. (See Preventing leaks.)
• Inspect the needle guide for sample residue or debris, which can cause carryover. If necessary, clean or replace the guide.
• Avoid plate or vial sealing systems that use sticky substances, which can cause carryover.
• If you suspect sample interaction with the needle material, increase the strength of the wash solvent, or increase the wash time.
• When selecting wash solvents, follow these Purge and wash solvent guidelines.