A hyphenated methodbased on HPLC in combination with amperometric determination (AD)for adenine, caffeine, theophylline and TB was presented by Meyeret al. The authors used GCE as working electrode in wall jet arrange-ment with a detection potential set on +1.4 V after elimination ofmatrix effects by application of solid-phase extraction (SPE) resulting inLOD of 2.5 ng for TB .