Antibiotic standards stored as a mixture in water: methanol are unstable at various temperatures irrespective of pH and glass container silanization
Creators: name: Emami, Shiva
name: Lerno, Larry A.
name: Taha, Ameer Y.
Publisher: name: Taylor & Francis
Year: 2021
Subjects: subject: Biochemistry
subject: Space Science
subject: Medicine
subject: Physiology
subject: FOS: Biological sciences
subject: Pharmacology
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: Immunology
subject: FOS: Clinical medicine
subject: 69999 Biological Sciences not elsewhere classified
subject: 110309 Infectious Diseases
subject: FOS: Health sciences

description: It is well-established that antibiotics stored individually at their optimal pH and in appropriate solvents are stable over time. However, limited information exists on the stability of antibiotics from multiple classes when prepared and stored as a mixture prior to multiresidue analysis by mass spectrometry. This study tested the stability of antibiotic standard mixtures from eight classes [amphenicols, tetracyclines, sulfonamides, quinolones, macrolides, β-lactams, lincosamides and miscellaneous (i.e., trimethoprim)] in relation to the water:methanol ratio, presence of sodium hydroxide base (to solubilise quinolones), storage temperature, and container type including plain and silanized glass vials. Antibiotics were analysed by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry. Several antibiotics, mainly quinolones, tetracyclines and macrolides, were unstable when stored as mixtures for one week regardless of the water:methanol ratio, storage temperature (4, −20 or −80 °C) and presence/absence of sodium hydroxide. Silanization of glassware improved the storage stability of quinolones and macrolides but reduced the stability of tetracyclines and other antibiotics including florfenicol amine, penicillin G, erythromycin and sulfadiazine. Our results show that several antibiotics in water:methanol are unstable when stored as a mixture and suggest a limited advantage of using base or silanized glass vials for the preparation and storage of antibiotic standards mixed together. Freshly prepared antibiotic standard mixtures are recommended for multi-residue quantitation of antibiotics. <b>Abbreviations</b> AMOX: amoxicillin; AMP: ampicillin; AZ: azithromycin; CAP: chloramphenicol; CE: collision energy; CTC: chlortetracycline; CIP: ciprofloxacin; DOX: doxycycline; ENO: enoxacin; ENRO: enrofloxacin; ERYTH: erythromycin; FF: florfenicol; FFA: florfenicol amine; FLU: flumequine; HDPE: high-density polyethylene; LC-MS/MS: liquid chromatography–tandem mass spectrometry; LIN: lincomycin; MRM: multiple reaction monitoring; NOR: norfloxacin; OFL-D3: ofloxacin-D3; OXO: oxolinic acid; OTC: oxytetracycline; PEN-G: penicillin G; PEN-V: penicillin V; ROX: roxithromycin; SDM: sulfadimethoxine; SDZ: sulfadiazine; SMX: sulfamethoxazole; SMZ-D4: sulfamethazine-D4; SSZ: sulfasalazine; TC: tetracycline; TAP: thiamphenicol; TILM: tilmicosin; TRIM: trimethoprim; TL: tolerance limit; VIRG: virginiamycin; UPLC-MS/MS: ultra-high pressure liquid chromatography–tandem mass spectrometry.