Determination of antibiotics (tetracyclines and sulfonamides) in biosolids by pressurized liquid extraction and liquid chromatography–tandem mass spectrometry

• The method is based on PLE followed by a clean-up with HLB cartridges and analysis by liquid chromatography–tandem mass spectrometry.
• High recoveries ranging from 90.4 to 100.9% are obtained for 4 sulfonamides and 4 tetracyclines.
• MLDs range from 0.6 to 4.2 ng/g for sulfonamides and 3.2 to 13 ng/g for tetracyclines.
• The method is successfully applied to the analysis of sewage sludges from wastewater treatment plants in Spain.

A robust and sensitive analytical method is developed to quantitatively determine tetracyclines and sulfonamides, two major antibiotic classes, in sewage sludge. The antibiotic agents, oxytetracycline, tetracycline, dioxycycline, chlorotetracycline, sulfathiazole, sulfapyridine, sulfamethazine and sulfamethoxazole, were extracted using pressurized liquid extraction (PLE) with citric acid at pH 3 and methanol (1:1 v/v). Clean-up of the extracts was performed by solid phase extraction (SPE) with hydrophilic–lipophilic balance cartridges. Identification and quantification of the compounds is by liquid chromatography–tandem mass spectrometry in multiple reaction monitoring (MRM) mode. High recoveries ranging from 90.4 to 99.9% for sulfonamides and 96.2 to 100.9% for the tetracyclines are obtained. Method detection limits (MDLs) range from 0.6 to 4.2 ng/g for sulfonamides and 3.2 to 13 ng/g for tetracyclines. After validation, the method is applied to the analysis of sludges collected from different WWTPs in Spain.