On-line coupling of solid-phase extraction to liquid chromatography–tandem mass spectrometry for the determination of macrolide antibiotics in environmental water

An automated on-line solid-phase extraction–liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS) system was developed for the determination of macrolide antibiotics including erythromycin (ETM), roxithromycin (RTM), tylosin (TLS) and tilmicosin (TMC) in environmental water samples. A Capcell Pak MF Ph-1 column packed with restricted access material (RAM) was used as SPE column for the concentration of the analytes and clean-up of the sample. One milliliter water sample was injected into the conditioned SPE column and the matrix was washed out with 3 mL high purity water. By rotation of the switching valve, macrolides (MLs) were eluted in the back-flush mode and transferred to the analytical column by the chromatographic mobile phase. The matrix effect was evaluated by the directly injection LC–MS and on-line SPE–LC–MS methods. The limits of detection (LODs) and limits of quantification (LOQs) obtained are in the range of 2–6 and 7–20 ng L−1, respectively, which means that the proposed method is suitable for trace analysis of MLs at low level concentration. The intra- and inter-day precisions are in the range of 2.9–7.2% and 3.3–8.9%, respectively. In the three fortified levels (20, 200 and 2000 ng L−1), recoveries of MLs ranging from 86.5% to 98.3% are obtained.