Sulfametoxydiazine

All reagents used in this experiment were at least analytical grade. All the ultrapure water used in the experiment was obtained through Milli-Q (Millipore, Bradford, MA, USA). Ten sulfonamides: sulfamethoxazole (SMZ), sulfafurazole (SIZ), sulfamethizole (SMT), sulfadiazine (SD), sulfadimidine (SM2), sulfametoxydiazine (SMD), sulfadoxine (SDM′), sulfapyridine (SPD), sulfathiazole (ST), sulfamethoxypyridazine (SMP) were purchased from Sigma. 1,3,5-Triformylphloroglucinol (Tp), glycol, diglycolic anhydride (DA), 1,6-hexanediamine, benzidine (BD), and FeCl₃·6H₂O were purchased from Aladdin (Shanghai, China). Ethanol, N,N-dimethylformamide (DMF), tetrahydrofuran (THF), mesitylene, and 1,4-dioxane were purchased from Concord Chemical Research Institute (Tianjin, China). HNO₃ were obtained from Guangfu Fine Chemical Research Institute (Tianjin, China). All glassware should be soaked in aqua regia (HCl : HNO₃ = 3 : 1, v/v) for at least 24 h and cleaned with ultrapure water.

The chemical reagents employed were commercially available. Methanol (MeOH), acetonitrile (ACN), formic acid (FA) and water as mobile phase of LC-MS pure grade were purchased from Merck (Shanghai, China). Analytical grade solvents were purchased from Guangzhou Chemical Regent Factory (Guangzhou, China). Other reagents were all purchased from Aladin (Shanghai, China). The sieve plates for SPE column were made in polypropylene with the pore size of 20 μm.
The standard of nine single antibiotic, sulfadiazine (SDZ), sulfadimidine (SMZ), tetracycline (TC), sulfametoxydiazine (SME), oxytetracycline (OTC), sulfadoxine (SDO), chlortetracycline (CTC), sulfachloropyridazine (SCP), doxycycline (DC) were purchased from Sigma-Aldrich (Saint Louis, USA). The stock solution of the mixed standard were prepared as 10 mg L⁻¹ in methanol/water (1 : 1, v/v), and stored at 4 °C in darkness. Different calibration solutions were prepared daily, by dilution of the stock solution with methanol/water (1 : 4, v/v).