The widespread use of antibiotics in veterinary medicine for prophylactic, therapeutic and growth promoting purposes may result in the presence of residues in foodstuff of animal origin. Sulfonamides, N-derivatives of 4-amino-benzenesulfonamide, belong to a diverse class of synthetic antibiotics consisting of chemically related compounds. A number of them e.g., sulfamethazine, sulfadiazine, sulfaquinoxaline and sulfamethoxypyridazine, are widely used in animal husbandry. Their residues in food are of great concern because of their potential carcinogenic character and because they may contribute to the development of antibiotic resistance in humans. These facts have induced most of the regulatory activities on sulfonamides. Regulatory bodies in the European Union as well as in other countries have set different maximum residue limits in various tissues. These regulations have stimulated the development of fast, accurate and sensitive analytical methods for monitoring sulfonamide residues in food samples of animal origin. Gas chromatography methods tend to be timeconsuming due to the required previous cleanup and derivatization procedures, thus, HPLC methods with UV or MS detection have the leading position. These and other aspects of current analytical methodology, including sample preparation and cleanup, are reviewed and discussed. Emphasis is given to confirmatory methods since these comprise useful tools to regulatory agencies, and identifications based on these methods can be used in support of regulatory action.

A HPLC method with diode-array detection, at 265 nm, was developed and validated for the determination of ten sulfonamides (SAs): sulfadiazine (SDZ), sulfathiazine (STZ), sulfamethoxine (SMTH), sulfamethizole (SMZ), sulfamethoxypyridazine (SMPZ), sulfamonomethoxine (SMMX), sulfamethoxazole (SMXZ), sulfisoxazole (SIX), sulfadimethoxine (SDMX), and sulfaquinoxaline (SQX) in milk. A mixture of ethyl acetate, n-hexane, and isopropanol was used for the extraction of target analytes from milk. The mobile phase, a mixture of 0.1% v/v formic acid, CH(3) CN, and CH(3) OH was delivered to the analytical column under a gradient program. The procedure was validated according to the European Union regulation 2002/657/EC in terms of selectivity, stability, decision limit, detection capability, accuracy, and precision. Mean recoveries of sulfonamides from milk samples spiked at three concentration levels (0.5×MRL, 1×MRL, and 1.5×MRL) (MRL, maximum residue level) were 93.9-115.9% for SDZ, 97.8-102.9% for STZ, 94.6-107.0% for SMTH, 98.3-111.5% for SMZ, 95.3-108.4% for SMPZ, 97.9-106.0% for SMMX, 97.6-111.3% for SMXZ, 94.3-104.6% for SIX, 96.4-109.1% for SDMX, and 98.2-111.2% for SQX. All RSD values were lower than 8.8%. The decision limits CCa calculated by spiking 20 blank milk samples at MRL (100 μg/kg) ranged from 101.61 to 106.84 μg/kg, whereas the detection capability CCb ranged from 105.64 to 119.01 μg/kg.

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