Schänzer, W., Gotzmann, A., Geyer, H., & Marek-Engelke, U. (1998). The Cologne protocol to follow-up positive caffeine cases. Recent advances in doping analysis (5) : Proceedings of the Manfred Donike Workshop ; 15th Cologne Workshop on Dope Analysis ; 23rd to 28th February 1997, 1998. S. 259-268, Lit..

Schänzer, Wilhelm, Andrea Gotzmann, Hans Geyer, and U. Marek-Engelke. "The Cologne Protocol to Follow-up Positive Caffeine Cases." Recent Advances in Doping Analysis (5) : Proceedings of the Manfred Donike Workshop ; 15th Cologne Workshop On Dope Analysis ; 23rd to 28th February 1997 1998: 1998. S. 259-268, Lit..

Schänzer, Wilhelm, Andrea Gotzmann, Hans Geyer, and U. Marek-Engelke. "The Cologne Protocol to Follow-up Positive Caffeine Cases." Recent Advances in Doping Analysis (5) : Proceedings of the Manfred Donike Workshop ; 15th Cologne Workshop On Dope Analysis ; 23rd to 28th February 1997 1998: 1998. S. 259-268, Lit..