||A reliable analytical method for the determination of sulfonamide antibiotics in Gaoping River waters was developed. Solid phase extraction was used for sample pretreatment. First, the SPE cartridges were conditioned with 5 mL of methanol and balanced with 5 mL of ultrapure water, then 500 mL of water sample was loaded into the SPE cartridges. Next, the SPE cartridges were washed with 5 mL of ultrapure water and dried for 30 minutes in vacuum. Analytes were eluted from the cartridges with 5 mL of methanol, and then dried under a gentle flow of nitrogen gas, reconstituted by 1 mL of methanol, and transferred into a sample vial. Ten sulfonamide antibiotics including sulfadiazine(SDZ), sulfathiazole(STZ), sulfaphenazole(SNZ), sulfachloropyridazine(SCP), sulfamethazine(SMZ), sulfadimethoxine(SDM), sulfaquinoxaline(SQX), sulfamonomethoxine(SMM), sulfamerazine(SMR), sulfamethizole(SMT) were analyzed by LC-MS/MS equipped with a mobile phase composed of 0.005 M ammonium acetate and methanol to perform gradient elution. The recovery rates were 52.1-86.8 %, limit of detection were 1.4-3.3 ng/L and limit of quantitation were 4.8-11.14ng/L.|
On October 2, 2013(wet season), and February 6, 2014(dry season), environmental water samples were collected from six sampling sites along the Gaoping River to investigate the contents of sulfonamide. Contents of SDZ, STZ, SNZ, SCP, SDM, SQX, SMM, SMR, SMZ and SMT were 1.8-513.3 ng/L, N.D.-574.2 ng/L, N.D.-6.8 ng/L, 6.7-412.5 ng/L, 2.6-77.3 ng/L, N.D.-28.0ng/L, 4.5-76.1 ng/L, N.D.-6.8 ng/L, N.D. and N.D. Concentrations of the measured sulfonamide antibiotics for water samples collected on October 2, 2013 were slightly lower than February 6, 2014, due to the difference in the amount of rainfall.
The concentrations of sulfonamide antibiotics at Gaoping Estuary were higher than the upper mainstream sampling sites Liling Bridge and Gaoping Bridge which is attributed to the inlet of two tributaries with high contents of sulfonamides.