increasing baseline at HPLC

[trkgen]

Im performing TAG analysis of corn oil ussing a 100% methanol gradient to 100% isopropanol gradient on an 250mm 4.6 mm diameter 5 micromeer C18 coloumn and uv detector at 210nm and got satisfactioary results but after 3 mounts I wanted to repeate my run and had an increasing base line till 2000mabsorbance could it be due to dissolved oxigen in isopropanol what should I do plz help me

[Mark Tracy]

Dissolved oxygen has only a very small effect at 210 nm. You most likely have contamination. First check the methanol and isopropanol to see if they are contaminated. Then try washing the column 15 minutes each with methanol, then acetone, then dichloromethane, then back to methanol. Be patient.