HPTLC determination of caffeine in urine

Sport associations allow athletes to consume food containing caffeine during competitions. Because stimulants like amphetamines and ephedrines can be readily detected in urine, athletes often resort to caffeine as a stimulant.
In 1987, the Medical Commission of the International Olympic Committee (IOC) determined the limit for caffeine in urine at 12 mg/L.
Caffeine is extracted from urine with chloroform after increasing the ionic strength by the addition of sodium chloride. The extract is chromatographed on silica gel. Densitometric quantification is performed by absorbance at 254 nm. Recovery (n=9) was found to be 100.8%, the precision of the method is 1.0%. The caffeine fraction in the unknown is positively identified by in-situ spectroscopy.