Gas Chromatographic–Mass Spectrometric Determination of Azithromycin in Biological Fluids: An Experimental Investigation

Background: Antibiotics are now widely used in food-producing animals to maintain optimal health and promote growth. Azithromycin monohydrate is an antibiotic that belongs to the macrolide antibiotic class. It is used to treat sexually transmitted diseases, upper and lower respiratory tract infections, and skin structure infections as an effective antibiotic. Methods: A gas chromatographic–mass spectrometric (GC–MS) method for determining azithromycin monohydrate residue in biological fluids is described. Using single-ion monitoring (SIM), this method detects residual azithromycin (AZM) in biological fluids. The confirmation by a full-scan electron impact (EI) mass spectrum is possible if residual level in a sample is >5 g/mL. AZM is extracted from a sample with chloroform and cleaned up with n-hexane washing before partitioning between chloroform and phosphate buffer solution. At room temperature, the cleaned extract is acetylated in an acetic anhydride–pyridine mixture (1:2). Results: The reaction mixture is injected into the GC–MS apparatus, and the detection has been conducted using SIM at m/z 200. The detection limit is 2 g/mL. Conclusions: This proposed method has the potential to be successfully applied to drug analysis in both forensic and toxicological laboratories.