Chromatography Forum

I´m analyzing Olanzapine, raw material, by USP 34 method. I´m doing Related compounds, and I´m having problems on stabilizing the gradient. The gradient begins to rise at 10 min on Mobile phase B for ten minutes, plateau from 20-25, and initial conditions at 27, and ends at 35. The problem is that is never the same shape of the base line, and I´m pretty sure I have stabilized it before each run, because I let it run for ten minutes longer after 35 minutes. I´m using a Luna C8, and the mobile phase A and B are different compositions of Acetonitrile and Sodium lauryl sulphate buffer. System temperature is 35 °C. Sometimes the gradient goes up to 200 mAU, and the next run goes to 15 mAU for example, randomly. Anyone knows what could it be happening?

Ion-pair reagents are notoriously slow to equilibrate and are also temperature sensitive. So:
- try equilibrating longer.
- tee a thermocouple into the flow stream just ahead of the column and monitor the mobile phase temperature to see if there is some correlation there.