Development of Dispersive Solid-phase Extraction Combined with Air-assisted Liquid-Liquid Microextraction for Determination of Sulfonamide Residues in Pasteurized Milk Samples using High Performance Liquid Chromatography

One of the significant contaminants in animal-derived foods, such as milk, is antibiotic residues, which put consumers' health at risk. Monitoring the amount of antibiotic residue in milk is crucial in order to alert the nation's health authorities and in this regard, several researches have been conducted for determination of different antibiotic residues in milk using various traditional and chromatographic methods. In this study, an efficient method for determining the residual levels of some sulfonamides in pasteurized milk was developed and presented.

After dispersive solid-phase extraction combined with air-assisted liquid-liquid microextraction of analytes, the residues of sulfadiazine, sulfamethoxazole, and sulfamethazine in the pasteurized milk were determined using HPLC with a diode array detector. Following the evaluation of the effective factors in the extraction and optimizing them, the validation of method was carried out by calculating analytical parameters such as linear range, LOD, LOQ, repeatability, and extraction recovery.

In the developed two-step extraction method, satisfactory figures of merit were obtained, therefore the method's linearity was shown with a coefficient of determination higher than 0.995. The limits of detection and measurement were less than 1.2 and 3.2 ng ml-1, respectively, which is less than the MRLs established for these antibiotics in milk. The analysis of real samples showed the presence of sulfamethoxazole in three milk samples in concentrations of 13±0.1, 9±0.2 and 9.6±0.5 ng ml-1 and no other antibiotics were discovered in the examined samples.

Overall, the established approach is a sensitive, accurate and reliable method and has high efficiency in determining selected antibiotics in milk samples.