Guaraná is a tropical fruit that grows in northeastern Brazil, from which a popular soft drink is manufactured. The main methylxanthine (MX) in the guaraná powder is caffeine (CF). Theobromine (TB) and theophylline (TP) are present in much lower concentrations. Because of the popularity of this soft drink, and the stimulating effects of MXs, we introduced an undergraduate project on their extraction from guaraná powder and subsequent analysis. Literature showed that the values of λmax and εmax of CF, TB and TP are very close. Consequently, determination of their concentrations is, at best, difficult. We discussed this problem with the chemistry students of an advanced experimental course, and asked for a solution. These students (36) were in their seventh semester and had a spectroscopy course. They suggested use of chromatographic separation, followed by mass spectrometry (MS) detection. The following project was carried out: (i) Optimization of the extraction of guaraná powder by aqueous ethanol using chemometrics. The experimental variables were alcohol volume fraction, fEtOH, and powder extraction time, t; (ii) Calculation of the apparent CF concentration from the extract absorbance at 272.5 nm; (iii) Analysis of the extracts by LC-MS. Chemometrics showed that the effect of fEtOH on the extraction yield was more important than extraction time. The three MXs were separated by LC, using acidified aqueous methanol. Use of electrospray ionization (3 eV) solved the MX structure identification problem only partially because TB and TP have the same molar mass. Using LC-MS/MS (30-40 eV) solved this problem; TB and TP have distinct retention times and fragmentation patterns. This project is safe and relevant because of the popularity of CF-containing drinks (guarana, coffee, tea), and health concerns about abuse of CF consumption. Students assessment was based on their data presentation, and discussion of aspects of the project.

Analysis of consumer products: Application of chemometrics and LC-MS/MS for the simultaneous analysis of caffeine and other methylxanthines in guaraná powder extract

ACS Spring Meeting 2021

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