Thesis (M.Sc.)--Chulalongkorn University, 2015

A cost-effective spectroelectrochemical flow-cell was developed for determination of caffeine content in beverages. The developed flow-cell which coupled with sequential injection analysis (SIA) system can be applied for spectrophotometric and electrochemical studied in the same device. The flow-cell body was made of acrylic plastic material that is lightweight, hard and chemically inert. Its dimension was 34mm × 50mm × 15mm. The flow-cell consisted of 2 optical fiber probes with a path length of 10 mm for spectrophotometric investigated at the wavelength of 273 nm. Glassy carbon was chosen as a working electrode for caffeine oxidation studied by square wave voltammetry technique at the potential of 1.4 V vs Ag/AgCl in phosphate buffer solution. The linear ranges of caffeine determination were 0.01-0.12 mM and 0.05-0.5 mM with detection limit of 1.00 µM and 3.10 µM for spectrophotometric and electrochemical method, respectively. The reproducibility was studied and the relative standard deviation percentages (%RSD) were 3.21% and 4.98% for spectrophotometric and electrochemical measurements, respectively. This developed flow-cell is small, cost-effective and easy to connect with sequential injection analysis system. Moreover, the developed spectroelectrochemical flow-cell was successfully applied for the determination of caffeine in beverages samples and the results were insignificantly different when compare with a standard method.