Simultaneous determination of fluoroquinolone and tetracycline antibacterials in sewage sludge using ultrasonic-assisted extraction and HPLC-MS/MS

Abstract

A reliable method was proposed for the simultaneous determination of five fluoroquinolones (FQs) and two tetracyclines (TCs) in sewage sludge using ultrasonic-assisted extraction (USE) followed by SPE cleanup and high-performance liquid chromatography-mass spectrometry (HPLC-MS)/MS analysis with electrospray ionisation (ESI) in a positive mode. The USE conditions (e.g. extraction solvent, pH, and extraction cycles) and high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) parameters were optimised. Quantification was performed by internal standard calibration in multiple reaction monitoring mode. Recoveries of the antibacterials ranged from 41 to 123%, with relative standard deviations within 17%. The sample-based limits of quantification were 10–63 ng g⁻¹ dry weight (dw) for FQs (ciprofloxacin, enrofloxacin, lomefloxacin, norfloxacin, and ofloxacin) and 250–500 ng g⁻¹ dw for TCs (tetracycline and oxytetracycline). The method was applied to determine the antibacterials in sewage sludge and sediment samples were collected from the Pearl River Delta, China. Ciprofloxacin, norfloxacin, and ofloxacin were frequently detected, ranging from 1052 to 17740 ng g⁻¹ dw in dewatered sludge samples, 585–3545 ng g⁻¹ dw in untreated solids, and 98–258 ng g⁻¹ dw in an urban stream sediment sample, respectively. Lomefloxacin and enrofloxacin were also occasionally detected.

Keywords:

• antibacterials
• sewage sludge
• ultrasonic-assisted extraction
• liquid chromatography – tandem mass spectrometry

Acknowledgements

This work was financially supported by the National Basic Research Program of China (No. 2009CB421604), GIG Innovation Program (No. GIGCX-07-01) and NSFC program (No. U0633005). We thank Mr Chen Huashan at the SKLOG for his assistance in HPLC-MS/MS. The personnel of the studied STPs are thanked for their help in sampling. This is contribution No. IS-1254 from GIGCAS. The anonymous reviewers are also appreciated for their comments and recommendations that have greatly improved this paper.