I've been quantifying an enzyme (carbonic anhydrase) using a C4 5um 150 x 4.6mm column (Jupiter from Phenomenex). I'm using a gradient of 20 to 80% 0.1% TFA in acetonitrile against 0.1% TFA in water. The peak shape is excellent. I'm experiencing positive drift in the baseline even at 280nm though. This did reduce when I followed the usual washing protocols. The thing is I'm not sure if I should be getting some drift and I don't know the column's history. It will take about a week for me to get a new column and I need the results sooner than that. We have a spectroscopist who uses our columns sometimes and I feel this may be source of contammination if there is any (they don't understand analytical quantities!).