Improvement of on-line solid-phase extraction for determining phenolic compounds in water

Modifying the most common design for the on-line coupling of a precolumn to reversed phase LC with diode array detection has resulted in reduction of the broadening of the peaks which results when the compounds of interest are strongly retained by a highly hydrophobic sorbent. The modification consists of the desorption of the analytes trapped on the precolumn solely by the organic solvent used to modify the solvent strength of the mobile phase. Results obtained using this design were compared with those obtained with the conventional design, with C18and PLRP-S precolumns. The performance of the system was also tested with a highly cross-linked styrene-divinylbenzene copolymer (ENVI-chrom P) precolumn for the determination of phenolic compounds in real samples. The advantages and disadvantages are discussed. Ion-pair solid phase extraction is used in order to increase the breakthrough volumes of more polar compounds, mainly phenol. The use of the new design enables phenolic compounds to be determined at the low µg L−1level with limits of detection ranging between 0.1 and 2 µg L−1in tap water when a 10 mL sample was analyzed.