HPLC Products

Sample carryover occurs if a trace of the previous sample remains on or in the needle when it is inserted into the next sample vial.

Some autosamplers minimise this by leaving the needle in the flow path (making it a part of the loop) so that in the inject position, the needle is flushed with eluent throughout the run. Others have various wash cycles which can be run before or after each sample or each injection.

To test for sample carryover, it is necessary to follow an sample injection with a blank (an injection from a vial of clean solvent). Extreme care must therefore be taken to ensure that the vial and solvent is clean! If doing a gradient run, ghost peaks may appear which are nothing to do with the sample, and these will appear if a blank gradient run is performed without making any injection at all. Carryover must involve peaks which were present in the previous injection.

If the current wash routine is proving inadequate to prevent carryover, check the procedure. You can change the wash solvent, perform two or even more procedures between each run. Also watch out for contamination arising from sample on the outside of the needle. Some autosamplers have the option of washing the needle in a wash port, and then air-drying the outside of the needle. The Sykam model does this and we would be pleased to advise if required.