Institute of Chemical Technologies and Analytics, TU Wien, Getreidemarkt 9/164, 1060 Vienna, Austria.
Centre for Advanced Photonics and Process Analysis, Munster Technological University, Bishopstown, T12 P928 Cork, Ireland.
Sensors (Basel). 2024 Mar 20;24(6):1974. doi: 10.3390/s24061974.
Caffeine is the most widely consumed stimulant and is the subject of significant ongoing research and discussions due to its impact on human health. The industry's need to comply with country-specific food and beverage regulations underscores the importance of monitoring caffeine levels in commercial products. In this study, we propose an alternative technique for caffeine analysis that relies on mid-infrared laser-based photothermal spectroscopy (PTS). PTS exploits the high-power output of the quantum cascade laser (QCL) sources to enhance the sensitivity of the mid-IR measurement. The laser-induced thermal gradient in the sample scales with the analytes' absorption coefficient and concentration, thus allowing for both qualitative and quantitative assessment. We evaluated the performance of our experimental PTS spectrometer, incorporating a tunable QCL and a Mach-Zehnder interferometer, for detecting caffeine in coffee, black tea, and an energy drink. We calibrated the setup with caffeine standards (0.1-2.5 mg mL) and we benchmarked the setup's capabilities against gas chromatography (GC) and Fourier-transform infrared (FTIR) spectroscopy. Quantitative results aligned with GC analysis, and limits of detection matched the research-grade FTIR spectrometer, indicating an excellent performance of our custom-made instrument. This method offers an alternative to established techniques, providing a platform for fast, sensitive, and non-destructive analysis without consumables as well as with high potential for miniaturization.
咖啡因是最广泛消费的兴奋剂，由于其对人类健康的影响，目前正在进行大量的研究和讨论。由于行业需要遵守特定国家的食品和饮料法规，因此监测商业产品中的咖啡因含量变得尤为重要。在本研究中，我们提出了一种基于中红外激光光热光谱（PTS）的咖啡因分析替代技术。PTS 利用量子级联激光器（QCL）源的高功率输出来提高中红外测量的灵敏度。样品中的激光诱导热梯度与分析物的吸收系数和浓度成正比，从而可以进行定性和定量评估。我们评估了我们的实验 PTS 光谱仪的性能，该光谱仪结合了可调谐 QCL 和马赫-曾德尔干涉仪，用于检测咖啡、红茶和能量饮料中的咖啡因。我们使用咖啡因标准品（0.1-2.5 mg/mL）对设置进行校准，并将设置的能力与气相色谱（GC）和傅里叶变换红外（FTIR）光谱进行基准测试。定量结果与 GC 分析一致，检测限与研究级 FTIR 光谱仪相匹配，表明我们定制仪器的性能非常出色。该方法为现有的技术提供了替代方案，提供了一个快速、灵敏、非破坏性的分析平台，无需消耗品，并且具有高度的小型化潜力。
