On-line solid-phase extraction in liquid chromatography using restricted access pre-columns for the analysis of s-triazines in humic-containing waters

Abstract

A coupled-column liquid chromatographic system using solid-phase extraction pre-columns for the seven chlorotriazines, atrazine, desethylatrazine, desisopropylatrzine (DIA), propazine, simaize, desthylterbythylazine and terbuthylazine, using photodiode-array detection (PDAD) was developed. Restricted access (RA), was investigated as a pre-column material, making use of non-adsorptive size exclusion of macromolecules and simultaneous dynamic portioning of the analytes, for the pre-concentration in environmental analysis. The RA phase was characterized and shown to solve problems with difficult matrix effects in humic-containing surface water samples. Other pre-column materials, e.g. reversed-phase C 18, mono-functional C 18, extraction disk mixture of C 18 and styrene-divinylbenzene (PS-DVB) and LiChrolut EN, a polymeric sorbent specially designed for environmental analysis, were investigated and compared for their selectivity and stability, respectively. Comparisons were made with respect to selectivity and efficiency for the SPE columns separately and in combination with analytical columns. Recovery data and matrix dependencies were studied at concentration levels ranging between 0.1–10 μg/1. The RA pre-columns showed superior stability in complex environmental matrices, such as reference humic water and river water, due to the restriction of macromolecules. Retention properties with the RA alkyl-diol-silica were not sufficient for the most polar metabolites. However, efficient sorption/desorption kinetics were found with medium-polar and non-polar compounds. LiChrolut EN was found to strongly retain these polar metabolites as well as medium and non-polar solutes, and was selected for a deeper investigation (e.g. salinity dependence and pH). For a 10×2 mm I.D. pre-column, the breakthrough volume for the polar metabolite DIA was at least 150 ml, while for the RA pre-columns it was less than 10 ml. Unfortunately, this polymeric support was strongly effected, in terms of stability, in complex matrices which lead to repeated and expensive exchanging of pre-columns. However, in order to detect even the polar metabolites these pre-columns were finally used on-line together with liquid chromatography PDAD and thermospray mass spectrometry for the determination of triazines in water samples from the Ebro river during different seasons of the year.