Fast Screening and Determination of Tadalafil in Pharmaceutics by Batch Injection Analysis (BIA) with Amperometric Detection

Tadalafil (TDL) is the active ingredient of Cialis®, one of the top selling drugs for the treatment of erectile dysfunction and very counterfeit worldwide. In this work, two amperometric methods are proposed for (1) determination and (2) screening of TDL in pharmaceutical products using a boron‐doped diamond electrode assembled in a 3D‐printed Batch Injection Analysis cell. Cyclic voltammograms showed that TDL presented one irreversible oxidation and pH dependent process at about 1.0 V (vs Ag/AgCl) with maximum current in Britton‐Robinson buffer pH 4.0. For the method 1, a constant potential of+1.3 V was applied and, under optimized conditions, good linear range for TDL quantification (from 1.0 to 150.0 μmol L−1), LOD of 1.0 μmol L−1 (experimental), high repeatability (RSD=1.9 %; n=20) and good sample throughput (270 h−1) were obtained. Method 1 was used for the determination of TDL in genuine and generic formulations, and the results were not statistically different from a comparative spectrophotometric method at a 95 % confidence level. In method 2, the multiple pulse amperometric detection (MPAD) was taken through the application of sequential potential pulses (+1.0, +1.2 and +1.5 V). The comparative profile of each sample was done after peak ratios from each amperogram (R1=ipa1.2V/ipa1.0V, R2=ipa1.5V/ipa1.2V, R3=ipa1.5V/ipa1.0V). This simple current normalization allowed the recognition of similar profiles between samples containing only TDL and differences between samples adulterated with other drugs (sildenafil, paracetamol, dipyrone, and caffeine). Finally, these methods are fast, use portable low‐cost apparatus and unmodified electrodes. Such features are attractive for routine analysis in forensic and pharmaceutical sciences.