Determination of sulfonamides in milk after precolumn derivatisation by micellar liquid chromatography

A simple method to identify and determine six sulfonamides (sodium sulfacetamide, sulfamethizole, sulfaguanidine, sulfamerazine, sulfathiazole and sulfamethoxazole) in milk by micellar liquid chromatography (MLC) is reported. The assay makes use of a precolumn diazotisation-coupling derivatisation including the formation of an azo dye that can be detected at 490nm. Furthermore, the use of MLC as an analytical tool allows the direct injection of non-purified samples. The separation was performed with an 80mM SDS-8.5% propanol eluent at pH 7. Analysis times are below 16min with a complete resolution. Linearities (r>0.9999), as well as intra- and inter-day precision (below 2.7%), were studied in the validation of the method. The limits of detection and quantification ranged from approximately 0.72 to 0.94 and 2.4 to 3.1ngmL−1, respectively. The detection limit was below the maximum residue limit established by the European Community. Finally, recoveries in spiked milk samples were in the 83–103% range.