[A quantitative micromethod for the caffeine determination (author's transl)].

A combined procedure with thin-layer-chromatography and densitometry is described for the quantitative estimation of caffeine in biological material. This method is applicable in the nanogram range. Test samples of less than 100 microliter may be used. The samples (capillary-blood) are extracted with the same volume of chloroform. Caffeine is separated from interfering compounds by thinlayer-chromatography. Commercial silica-60-plates with chloroform/acetone (9+1; v/v) as solvent are used. The running time is about 30 min. The quantitative densitometric determinations are performed in the remission mode at 273 nm. In the range from 10 to 60 ng/spot the calibration curve is linear. Accurate quantitative data will be obtained even at concentrations of 1 mg/l caffeine. The detection limit is at about 0.1 mg/l.