I'm trying to develop a method for analyzing ppm levels of sodium monochloroacetate using an organic acid column (REZEX ROA, H+ form) at room temp and 0.005N H2SO4 (0.5ml/min). The instrument is an HP1090 with autosampler. When I inject mobile phase onto the column (200ul), I get a peak at ~8 min (Vsub0?) and another at ~22 min. The area of the second peak is reproducible. This peak also appears in my standards at the same level. However, after running some samples (undiluted), then reinjecting mobile phase or standards, the peak grows much, much larger. Can anyone tell me what's happening?

I am not familiar with this column but may be able to offer assistance with some additional information. You don't specify your detector. Are you using UV or conductivity detection? Do you have any sense of the total permeation volume(i.e. the retention time of an analyte which has total access to both interstitial and resin pore volume)with this column?