Retention will be diminished if the isolate is ionised. The sample should be applied while the sorbent is still wet from the conditioning procedure. If the vacuum has been left on for more than one minute after conditioning, resolvate the cartridge by repeating the proper conditioning step prior to sample application. Retention is sometimes improved by slowing down the flow rate. This is done by adjusting the valve on the LiChrolut vacuum gauge or by using luer stopcocks on the LiChrolut cartridges.
Insufficient cleanup Interfering peaks or false positives appear during analysis.
Try various mixtures of solvents and buffers to achieve a selective wash step which removes the interferences but does not elute the isolate. Wash the cartridge with a solvent in which the isolate is not soluble. Try a more selective extraction mechanism. When appropriate, ion exchange extraction is generally more selective than polar extraction, and polar extraction is generally more selective than non-polar extraction Different sorbents can be stacked to remove entire classes of interfering compounds. For example, passing the sample through an SCX cartridge attached above a C18 cartridge will remove most cations before the sample reaches the C18.