On-line coupling of dynamic microwave-assisted extraction to solid-phase extraction for the determination of sulfonamide antibiotics in soil

A rapid technique based on dynamic microwave-assisted extraction (DMAE) coupled on-line with solid-phase extraction (SPE) was developed for the determination of sulfonamides (SAs) including sulfadiazine, sulfameter, sulfamonomethoxine and sulfaquinoxaline in soil. The SAs were first extracted with acetonitrile under the action of microwave energy, and then directly introduced into the SPE column which was packed with neutral alumina for preconcentration of analytes and clean-up of sample matrix. Subsequently, the SAs trapped on the alumina were eluted with 0.3% acetic acid aqueous solution and determined by liquid chromatography–tandem mass spectrometry. The DMAE parameters were optimized by the Box–Behnken design. Maximum extraction efficiency was achieved using 320 W of microwave power; 12 mL of extraction solvent and 0.8 mL min−1 of extraction solvent flow rate. The limits of detection and quantification obtained are in the range of 1.4–4.8 ng g−1 and 4.6–16.0 ng g−1 for the SAs, respectively. The mean values of relative standard deviation of intra- and inter-day ranging from 2.7% to 5.3% and from 5.6% to 6.7% are obtained, respectively. The recoveries of SAs obtained by analyzing four spiked soil samples at three fortified levels (20 ng g−1, 100 ng g−1 and 500 ng g−1) were from 82.6 ± 6.0% to 93.7 ± 5.5%. The effect of standing time of spiked soil sample on the SAs recoveries was examined. The recoveries of SAs decreased from (86.3–101.9)% to (37.6–47.5)% when the standing time changed from one day to four weeks.