A Tape Method for Fast Characterization and Identification of Active Pharmaceutical Ingredients in the 2-18 THz Spectral Range Eric Ofosu Kissi & Prince Bawuah & Pertti Silfsten & Kai-Erik Peiponen Received: 18 August 2014 /Accepted: 6 November 2014 / Published online: 20 November 2014 # Springer Science+Business Media New York 2014 Abstract In order to find counterfeit drugs quickly and reliably, we have developed ‘tape method’ a transmission spectroscopic terahertz (THz) measurement technique and compared it with a standard attenuated total reflection (ATR) THz spectroscopic measurement. We used well-known training samples, which include commercial para- cetamol and aspirin tablets to check the validity of these two measurement techniques. In this study, the spectral features of some active pharmaceutical ingredients (APIs), such as aspirin and paracetamol are characterized for identification purpose. This work covers a wide THz spectral range namely, 2-18 THz. This proposed simple but novel technique, the tape method, was used for characterizing API and identifying their presence in their dosage forms. By comparing the spectra of the APIs to their dosage forms (powder samples), all distinct fingerprints present in the APIs are also present in their respective dosage forms. The positions of the spectral features obtained with the ATR techniques were akin to that obtained from the tape method. The ATR and the tape method therefore, complement each other. The presence of distinct finger- prints in this spectral range has highlighted the possibility of developing fast THz sensors for the screening of pharmaceuticals. It is worth noting that, the ATR method is applicable to flat faced tablets whereas the tape method is suitable for powders in general (e.g. curved surface tablets that require milling before measurement). Finally, we have demonstrated that ATR techniques can be used to screen counterfeit antima- larial tablets. Keywords Terahertz . Antimalarial . Active pharmaceutical ingredients . Attenuated total reflection . Transmission spectroscopy J Infrared Milli Terahz Waves (2015) 36:278–290 DOI 10.1007/s10762-014-0123-7 E. O. Kissi (*) : P. Bawuah : P. Silfsten : K.<E. Peiponen Institute of Photonics, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland e-mail: atakissisnr@gmail.com P. Bawuah e-mail: prince.bawuah@uef.fi