University of the Basque Country, Faculty of Chemistry, Manuel Lardizabal 3, 20018 Donostia-San Sebastián, Spain.
Talanta. 2010 Apr 15;81(1-2):367-71. doi: 10.1016/j.talanta.2009.12.010. Epub 2009 Dec 16.
A quantitative method for the determination of caffeine, formic acid, trigonelline and 5-(hydroxymethyl)furfural (5-HMF) in soluble coffees by applying the proton nuclear magnetic resonance technique ((1)H NMR) is proposed. Each of these compounds records a singlet signal at the 7.6-9.5 ppm interval of the spectrum, and its area is used to determine the concentration. 3-(Trimethylsilyl)-2,2,3,3-tetradeuteropropionic acid is added in an exact known concentration as a reference for delta=0.00 ppm and as an internal standard. The method is applied to commercial soluble coffees and satisfactorily compared with results obtained by standard methods. The limits of detection and the coefficients of variation (N=10) are, respectively, 1.32 mg/g of solid product and 4.2% for caffeine, 0.45 mg/g and 2.6% for formic acid, 0.58 mg/g and 2.4% for trigonelline, and 0.30 mg/g and 7.3% for 5-HMF. The described method is direct and no previous derivatization is needed.
本文提出了一种应用质子核磁共振技术（1H NMR）定量测定速溶咖啡中咖啡因、甲酸、葫芦巴碱和 5-羟甲基糠醛（5-HMF）的方法。这些化合物在光谱的 7.6-9.5 ppm 区间记录单峰信号，其面积用于确定浓度。添加精确已知浓度的 3-（三甲基硅基）-2,2,3,3-四氘代丙酸作为 delta=0.00 ppm 的参考和内标。该方法应用于商业速溶咖啡，并与标准方法获得的结果进行了令人满意的比较。检测限和变异系数（N=10）分别为咖啡因 1.32mg/g 固体产物和 4.2%，甲酸 0.45mg/g 和 2.6%，葫芦巴碱 0.58mg/g 和 2.4%，5-HMF 为 0.30mg/g 和 7.3%。该方法直接，无需事先衍生化。
