Too much or too little caffeine? Determination of content in thermogenic capsules by quantitative 1H nuclear magnetic resonance (qNMR).

Caffeine-based thermogenic capsules have been widely used as stimulants, as well as for inducing the release of serotonin and dopamine. Regulatory agencies worldwide indicate that caffeine-based supplements should contain 210-420 mg per capsule. Excessive caffeine consumption can lead to a range of adverse effects, including anxiety, insomnia, digestive issues, palpitations, and high blood pressure, among other symptoms. In this context, this work aims to propose an alternative method for the qualification and quantification of caffeine in these products using quantitative Nuclear Magnetic Resonance (qNMR), which could also be applied to other caffeine-based drugs. As a result, the method using an internal standard was both selective and effective for caffeine quantification. We analyzed 11 real samples, finding significant discrepancies between the information presented on product labels. Six samples had caffeine content exceeding 115 % (Samples 1, 2, 4, 6, 7, and 10), three had content below 85 % (Samples 5, 8, and 9), and one sample contained only 4.3 % of the amount stated on the label (Sample 11). In summary, this article demonstrates the applicability of qNMR by 1H for determining the caffeine content in commercially available thermogenic capsules. In summary, it is a rapid method that requires no sample preparation and can be applied to both powder-based and oil-based products.