Le-Minh, Nhat, et al. Talanta, 2012, 89, 407-416.
A robust and sensitive LC-MS/MS method was developed in this work for the analysis of trace antibiotics in different complex wastewater matrices, including six sulfonamide antibiotics (sulfadiazine, sulfathiazole, sulfapyridine, sulfamerazine, sulfadimethazine, and sulfamethoxazole), two sulfonamide metabolites, and trimethoprim.
Isotopically labeled compounds were used as surrogate standards to correct for matrix effects, SPE recovery variability, and instrument variability of unlabeled compounds. Direct analog isotopic standards were used for all target analytes except sulfapyridine. In this work, sulfamerazine-d4 was used as a surrogate standard for sulfamerazine and sulfapyridine, as sulfapyridine isotopic analogs were not commercially available. Sulfamerazine-d4 was chosen as the isotopic standard for sulfapyridine because these chemicals have similar chemical structures and close chromatographic retention times.
The method has been fully validated in various wastewater matrices collected after varying degrees of treatment. The MDLs for all target compounds were 0.2 to 0.4 ng/mL for ultrapure water, 0.4 to 0.7 ng/mL for tap water, 1.4 to 5.9 ng/mL for lab-scale MBR mixed liquor, 0.7 to 1.7 ng/mL for effluent after biological treatment, and 0.5 and 1.5 ng/g dry weight for MBR sludge. Analytical matrix effects lead to significant and unpredictable signal suppression in complex matrices compared to ultrapure water. The use of isotopically labeled surrogate standards is essential to correct for matrix effects in trace organic analyses.
