Determination of caffeine in roasted coffee

Precision und recovery of three standard methods and one rapid method for the determination of caffeine in roasted coffee were tested: German Standard DIN 10777, part 2 (1986; abbreviation: AS35), ISO Standard 10095 (1992; ISO), German Standard DIN 10777, part 2 (1994; DIN) and the method of Stennert and Maier (1993; ST). The last mentioned three methods work with HPLC; of these also the detection limits and the contents in a normal and a decaffeinated coffee were determined. The values of the standard deviations increase in the order DIN < ISO < AS35 < ST, the recoveries in the order AS35 < ISO < DIN < ST and the determined amounts in the order ISO < DIN < ST (AS35 not tested). Reasons for the differences may be losses of caffeine in the kieselguhr columns (AS35), losses in the solid phase extraction column (ISO) and losses during the purification with MgO (ISO, DIN), differences in making up to volume (DIN) and interfering peaks (ST). In all the DIN Standard 10777, part 2, should be the best method.