Problem: Broadened or split peaks were observed on chromatogram of PP-ODS2. Dopamine seemed OK, but if magnified the peak was broadened as well. The retention times were  also slightly earlier. 100% methanol wash in the reverse direction did not correct the problem.

Solution: To correct, the PP-ODS2 column needs to be washed as follows. 

1. 30 min water in the reverse direction.2. 1 hr with 0.1% phosphoric acid in 100% acetonitrile (if not available 100% acetone) in the reverse direction3. 30 min water in the normal direction4.  Run analytical mobile phase overnight to lower the BGC.5. Re-check the separation.

We assume the contamination at the column top could not removed by methanol wash but could with acetonitrile.