Australian Centre for Research on Separation Science, School of Chemistry, Monash University, Clayton, VIC, Australia.
J Sep Sci. 2013 Jun;36(11):1774-80. doi: 10.1002/jssc.201201081. Epub 2013 Apr 27.
Caffeine test solute was employed in combination with an internal standard (IS), 1,4-dimethoxybenzene, in preparative-gas chromatography (prep-GC), with nuclear magnetic resonance (NMR) experiments. The IS served to: (i) quantify the trapping efficiency of an external trapping assembly, consisting of a capillary column cryotrap at the end of the analytical column; (ii) quantify the solute response in different NMR samples; and (iii) permit correlation of expected level of response of a compound in the NMR experiment, based on relative responses of the IS and solute in the GC result. The recovery rate of caffeine from multiple injections of sample (1×, 2×, 5× and 10×) was 69.6 ± 1.3%, which correlated well (R(2) = 0.999) with the number of injections of compound. The (1)H-NMR spectrum was sufficient to enable structural characterisation of the reference caffeine compound, and was achieved with recovery of amounts of ≤10 μg from a single aliquot. Less than 400 μg of collected caffeine (40 replicate injections) was sufficient for structural characterisation by (13)C-NMR spectral analysis. The method allows development of approaches to separate unknown compounds in complex samples, and to separately use MS and NMR for their characterisation.
采用咖啡因测试溶质，并结合内标（IS），1,4-二甲氧基苯，进行制备气相色谱（prep-GC），并结合核磁共振（NMR）实验。IS 的作用是：（i）量化外部捕集组件的捕集效率，该组件由分析柱末端的毛细管柱冷阱组成；（ii）量化不同 NMR 样品中的溶质响应；（iii）允许根据 IS 和溶质在 GC 结果中的相对响应，对 NMR 实验中化合物的预期响应水平进行相关。从样品的多次进样（1×、2×、5×和 10×）中咖啡因的回收率为 69.6±1.3%，与化合物的进样次数相关性很好（R²=0.999）。1H-NMR 谱足以实现参考咖啡因化合物的结构特征化，并且可以从单个等分试样中回收≤10μg 的量。从收集的咖啡因（40 个重复进样）中少于 400μg 即可进行（13）C-NMR 光谱分析，以进行结构特征化。该方法允许开发用于分离复杂样品中未知化合物的方法，并分别使用 MS 和 NMR 对其进行特征化。
