An ion chromatographic apparatus and method for on-column preconcentration of trace ionic contaminants for quantitative trace analysis by ion chromatography. The method includes the multi-cycle, sequential steps of loading and purging of sample solution into and out of a sample injection loop (26) to cumulatively preconcentrate a separator column (30) with a cumulative amount of sample. Each purging step includes directing pressurized liquid, at a substantially constant rate and for a predetermined period of time to the sample injection loop (26), to drive up to about 98 % of the known volume of the sample solution from the sample injection loop (26). In turn, this flushed volume of sample solution passes through an ion exchange resin column (30) for concentration of the trace ionic contaminants in the resin.