Ohira Shin-Ichi, Kuhara Kenta, Shigetomi Aki, Yamasaki Takayuki, Kodama Yuko, Dasgupta Purnendu K, Toda Kei
Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
Department of Chemistry, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan.
J Chromatogr A. 2014 Dec 12;1372C:18-24. doi: 10.1016/j.chroma.2014.10.077. Epub 2014 Oct 31.
Chromatographic determination of organic acids is widely performed, but the matrix often calls for lengthy and elaborate sample preparation prior to actual analysis. Matrix components, e.g., proteins, non-ionics, lipids etc. are typically removed by a combination of centrifugation/filtration and solid phase extraction (SPE) that may include the use of ion-exchange media. Here we report the quantitative electrodialytic transfer of organic acids from complex samples to ultrapure water in seconds using cellulose membranes modified with N,N-dimethylaminoethyl methacrylate, which essentially eliminates the negative ζ-potential of a regenerated cellulose membrane surface. The transfer characteristics of the ion transfer device (ITD) were evaluated with linear carboxylic acids. While the ion transfer efficiencies may be affected by the acid dissociation constants, in most cases it is possible to achieve quantitative transfer under optimized device residence time (solution flow rate) and the applied voltage. In addition, the transfer efficiency was unaffected by the wide natural variation of pH represented in real samples. The approach was applied to organic acids in various samples, including red wine, considered to represent an especially difficult matrix. While quantitative transfer of the organic acids (as judged by agreement with standard pretreatment procedures involving SPE) was achieved, transfer of other matrix components was <5%. The processed samples could then be chromatographically analyzed in a straightforward manner. We used ion exclusion chromatography with direct UV detection; in treated samples; there was a dramatic reduction of the large early peaks observed compared to only 0.45μm membrane filtered samples.
有机酸的色谱测定应用广泛，但在实际分析之前，样品基质通常需要进行冗长而精细的制备。基质成分，如蛋白质、非离子物质、脂质等，通常通过离心/过滤和固相萃取（SPE）相结合的方法去除，其中固相萃取可能包括使用离子交换介质。在此，我们报告了使用经甲基丙烯酸N,N-二甲基氨基乙酯改性的纤维素膜，可在数秒内将复杂样品中的有机酸定量电渗析转移至超纯水中，这基本上消除了再生纤维素膜表面的负ζ电位。使用直链羧酸评估了离子转移装置（ITD）的转移特性。虽然离子转移效率可能受酸解离常数的影响，但在大多数情况下，在优化的装置停留时间（溶液流速）和施加电压下可以实现定量转移。此外，转移效率不受实际样品中广泛存在的自然pH变化的影响。该方法应用于各种样品中的有机酸，包括被认为是特别难处理基质的红酒。虽然实现了有机酸的定量转移（通过与涉及SPE的标准预处理程序的一致性判断），但其他基质成分的转移率<5%。然后可以直接对处理后的样品进行色谱分析。我们使用离子排斥色谱法并直接进行紫外检测；在处理后的样品中，与仅经过0.45μm膜过滤的样品相比，观察到的大的早期峰显著减少。
