Determination of the total content of some sulfonamides in milk using solid-phase extraction coupled with off-line derivatization and spectrophotometric detection

A simple screening method for isolation and determination of the total content of some sulfonamides in milk using solid-phase extraction and a color reaction is described. This procedure is based on SPE of sulfonamides on hypercrosslinked polystyrene, elution with acetonitrile and off-line derivatization with p-dimethylaminocinnamaldehyde in acetonitrile followed by spectrophotometric determination. The reaction produces intense violet-red color and can be easily used both for quantitation of sulfonamides using spectrophotometry and for naked-eye semi-quantitative estimation. Maximum absorption of the reaction product was determined at 540 nm. The Lambert-Beer's law was obeyed in the range of 0.07-3.0 μg mL−1 in eluate, with the squared correlation coefficient (R2) of 0.9875-0.9995, and the relative standard deviation (RSD) of 3-4%. The limits of SAs detection using preconcentration were of 0.02-0.03 μg mL−1. The proposed method can be recommended as a routine screening method for quantitation of sulfonamides in milk.