Analysis of Trace Levels of Sulfonamide and Tetracycline Antimicrobials in Groundwater and Surface Water Using Solid-Phase Extraction and Liquid Chromatography/Mass Spectrometry

TLDR

A method was developed to trace six sulfonamides and five tetracyclines—antimicrobials used in veterinary and agricultural feed—that may leach into groundwater and surface water. The approach combines solid‑phase extraction with a Na₂EDTA‑coated macroporous copolymer and LC/MS using a positive‑ion electrospray, ammonium formate/formic acid buffer, methanol/water gradient, and mass‑spectral fragmentation for unequivocal identification. Quantitative recoveries of 98 ± 12 % were achieved at sub‑µg L⁻¹ levels, with sulfonamides identified by a characteristic m/z 156 ion and tetracyclines by neutral losses of 17 and 35 amu, though matrix effects required standard‑addition quantitation for the latter.

Abstract

A method has been developed for the trace analysis of two classes of antimicrobials consisting of six sulfonamides (SAs) and five tetracyclines (TCs), which commonly are used for veterinary purposes and agricultural feed additives and are suspected to leach into ground and surface water. The method used solid-phase extraction and liquid chromatography/mass spectrometry (LC/MS) with positive ion electrospray. The unique combination of a metal chelation agent (Na2EDTA) with a macroporous copolymer resulted in quantitative recoveries by solid-phase extraction (mean recovery, 98 ± 12%) at submicrogram-per-liter concentrations. An ammonium formate/formic acid buffer with a methanol/water gradient was used to separate the antimicrobials and to optimize the signal intensity. Mass spectral fragmentation and ionization characteristics were determined for each class of compounds for unequivocal identification. For all SAs, a characteristic m/z 156 ion representing the sulfanilyl fragment was identified. TCs exhibited neutral losses of 17 amu resulting from the loss of ammonia and 35 amu from the subsequent loss of water. Unusual matrix effects were seen only for TCs in this first survey of groundwater and surface water samples from sites around the United States, requiring that TCs be quantitated using the method of standard additions.