Detection and quantitative determination of furosemide (Lasix®) in urine

Furosemide is the most often prescribed diuretic. Combined with beta-receptor-blocker it is used for medical treatment of hypertonicity. Moreover, furosemide is abused in human as well as in horse sports for doping purposes and is therefore on the IOC (Int. Olymp. Committee) list of banned drugs.
The acidic urine extract is chromatographed on silica gel. Post chromatographic derivatization converts furosemide into azo dyes. Results can be verified by UV absorbance spectra of the underivatized substances. Densitometric quantification is performed by absorbance at 275 nm. Determination limit is about 0.2 mg/L, reliable detection limit about 0.1 mg/L