Detection and quantitative determination of chlortalidone (Hygroton®) in urine

Chlortalidone is an often used diuretic for the therapy. Moreover, it is abused in sports for doping purposes and is therefore on the IOC (Int. Olymp. Committee) list of banned drugs.
The alkaline urine extract is chromatographed on silica gel. Post chromatographic derivatization (with formaldehyde/sulfuric acid reagent) converts chlortalidone into a yellow dye. Results can be verified by UV absorbance spectra of the underivatized substances. Densitometric quantification is performed by absorbance at 240 nm. Determination limit is 0.2 mg/L, reliable detection limit about 0.1 mg/L.