ONLINE TRACE ENRICHMENT IN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY USING A PRE-COLUMN

The potential of on-line trace enrichment on a pre-column in high-performance liquid chromatography is demonstrated using phthalate esters as model compounds. The esters are concentrated onto a very shortr, i.e., ca. 2 mm long, plug of an apolar chemical bonded stationary phase (5-μm LiChrosorb RP-18). Analysis is performed on LiChrosorb RP-18 with a methanol step gradient as mobile phase; detection is done by UV absorption measurement at 233 nm. Phthalate ester recoveries are 95-100% even after enrichment from sample volumes of 500-1000 ml, with pumping speeds varying between 5 and 25 ml min-1. The single-column and the column-to-column reproductivity of the technique are usually 4-6% (relative standard deviation); band broadening due to the insertion of the pre-column is negligible. As an application, the determination of two esters in tap, distilled, mineral and river water, and in soft drinks, is reported. The trace enrichment of mixtures of polychlorinated biphenyls, and of chloroanilines, is also described. © 1979.