On-line biological sample cleanup for electrospray mass spectrometry using sol–gel columns

Using a slight overpressure, a urine sample is loaded onto a monolithic photopolymerized sol–gel column that has been derivatized with hydrophobic carbon chains and then the complex urine matrix is washed with aqueous solution. A buffer containing organic solvent is used to elute the adsorbed peptides by an applied voltage and the sample is then introduced into a mass spectrometer by sheath flow electrospray. The importance of desalting this type of sample is demonstrated by an experiment that shows that the signal intensity of a test solution with neurotensin, sprayed directly into the mass spectrometer, decreased from 4.5 × 104 cps to no detectible signal when just 10% urine is added to the sample solution. We suggest that this procedure may find general application for desalting biological samples prior to mass spectrometric analysis.