Has any one experienced random baseline drift as described below? What were you able to do to resolve the problem?

While using an isocratic ion-pair method run on a Zorbax SB Phenyl column, temperature controled at 30C, I have experienced drifting baseline for one or two injections which occurs randomly throughtout a run of 30 or more injections. This problem is reproducible on multiple systems using different columns and bathces of mobile phase. The drift (upwards or downwards) seems to occur for only one or two injections and then the baseline stabilizes again. The drift is sever enough to make integration difficult and if it occurs duing system suitablility the compounds of interest may not meet the %RSD criteria.

Could it be a late retained compound from one of the early injections?

Which kind of detector do you use?