Lignin film was deposited at the surface of glassy carbon electrode potentiostatically. In contrast to the unmodified glassy carbon electrode, an oxidative peak with an improved current and overpotential for caffeine at modified electrode showed catalytic activity of the modifier towards oxidation of caffeine. Linear dependence of peak current on caffeine concentration in the range 6 × 10−6 to 100 × 10−6 mol L−1 with determination coefficient and method detection limit (LoD = 3 s/slope) of 0.99925 and 8.37 × 10−7 mol L−1, respectively, supplemented by recovery results of 93.79–102.17% validated the developed method. An attempt was made to determine the caffeine content of aqueous coffee extracts of Ethiopian coffees grown in four coffee cultivating localities (Wonbera, Wolega, Finoteselam, and Zegie) and hence to evaluate the correlation between users preference and caffeine content. In agreement with reported works, caffeine contents (w/w%) of 0.164 in Wonbera coffee; 0.134 in Wolega coffee; 0.097 in Finoteselam coffee; and 0.089 in Zegie coffee were detected confirming the applicability of the developed method for determination of caffeine in a complex matrix environment. The result indicated that users' highest preference for Wonbera and least preference for Zegie cultivated coffees are in agreement with the caffeine content.
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机译：木质素膜恒电位沉积在玻璃碳电极表面。与未改性的玻璃碳电极相反，在改性电极上具有改善的电流和咖啡因的超电势的氧化峰显示出改性剂对咖啡因的氧化的催化活性。峰值电流对咖啡因浓度的线性依赖性，范围为6×10 −6 至100×10 −6 mol L -1 ，且具有确定系数和方法检出限（LoD = 3 s / slope）分别为0.99925和8.37×10 −7 mol L −1 ，辅以93.79–102.17％的回收率验证了开发的方法。试图确定在四个咖啡种植地区（Wonbera，Wolega，Finoteselam和Zegie）种植的埃塞俄比亚咖啡的水性咖啡提取物的咖啡因含量，从而评估用户喜好与咖啡因含量之间的相关性。与所报告的工作一致，Wonbera咖啡中的咖啡因含量（w / w％）为0.164； 0.134欧元的Wolega咖啡； 0.097欧元的Finoteselam咖啡；在Zegie咖啡中检测到0.089和0.089，这证实了所开发的测定复杂基质环境中咖啡因的方法的适用性。结果表明，用户最喜欢Wonbera，最不喜欢Zegie栽培咖啡与咖啡因含量一致。
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