Tolerance intervals modeling for design space of a salt assisted liquid-liquid microextraction of trimethoprim and six common sulfonamide antibiotics in environmental water samples.

Sulfonamides and trimethoprim combinations have been used extensively as antimicrobial agents for prevention and treatment of human and animal infections. Although many microextraction methods were developed for monitoring their residues in environmental water, none of these methods applied liquid-liquid microextraction for this purpose. This work presents for the first time a simultaneous Salt Assisted Liquid-Liquid Microextraction SALLME coupled with HPLC-UV for determination of trimethoprim and six common sulfonamide residues (sulfathiazole, sulfadiazine, sulfadmidine, sulfamethoxazole sulfadoxine and sulfaquinoxaline) in water samples. Co-extraction of trimethoprim with sulfonamides was achieved by the addition of perchloric acid as a chaotropic agent to the extraction medium. Quality by Design framework was applied to develop and optimize both of SALLME and HPLC steps to ensure procedure robustness and sensitivity. Tolerance interval modeling of SALLME responses was applied to construct the design space of SALLME procedure. The optimized HPLC system enabled fast, sensitive and robust separation the extracted compounds within four minutes. The method detection limits of the method were in the range of 2.15-7.64 ng.mL-1 . These values were far below the guidelines recommended limits (35 and 70 ng.mL-1 for each individual sulfonamide and trimethoprim respectively).