Hello,
We have a problem with sensitivity. Our recovery is inconsistent and continues to decrease. We just recently changed to a new column, however several samples have been ran. The column is a C18, 3um. Can you give us some advice on what maybe going on? Our system is a LCQ Advantage Mass Spec with a mobile phase of 1% formic acid in water. Thanks

Over time your MS ion source will become contaminated and need to be cleaned. The dirtier your samples, the more frequently you'll have to do this, unless you are taking measures (switching valves, pre-columns) to cleanup your samples online. Have you tried cleaning your source to see if sensitivity improves?