Analytical and Bioanalytical Development, Bristol-Myers Squibb, New Brunswick, NJ 08903-0191, USA.
J Pharm Biomed Anal. 2014 Jan;88:1-6. doi: 10.1016/j.jpba.2013.07.043. Epub 2013 Aug 21.
The classical internal standard quantitative NMR (qNMR) method determines the purity of an analyte by the determination of a solution containing the analyte and a standard. Therefore, the standard must meet the requirements of chemical compatibility and lack of resonance interference with the analyte as well as a known purity. The identification of such a standard can be time consuming and must be repeated for each analyte. In contrast, the external standard qNMR method utilizes a standard with a known purity to calibrate the NMR instrument. The external standard and the analyte are measured separately, thereby eliminating the matter of chemical compatibility and resonance interference between the standard and the analyte. However, the instrumental factors, including the quality of NMR tubes, must be kept the same. Any deviations will compromise the accuracy of the results. An innovative qNMR method reported herein utilizes an internal reference substance along with an external standard to assume the role of the standard used in the traditional internal standard qNMR method. In this new method, the internal reference substance must only be chemically compatible and be free of resonance-interference with the analyte or external standard whereas the external standard must only be of a known purity. The exact purity or concentration of the internal reference substance is not required as long as the same quantity is added to the external standard and the analyte. The new method reduces the burden of searching for an appropriate standard for each analyte significantly. Therefore the efficiency of the qNMR purity assay increases while the precision of the internal standard method is retained.
经典的内标定量 NMR（qNMR）方法通过测定含有分析物和标准品的溶液来确定分析物的纯度。因此，标准品必须满足化学兼容性要求，并且不能与分析物发生共振干扰，同时还需要已知的纯度。这种标准品的鉴定可能需要花费大量时间，并且必须针对每个分析物重复进行。相比之下，外标 qNMR 方法利用具有已知纯度的标准品来校准 NMR 仪器。外标品和分析物分别进行测量，从而消除了标准品与分析物之间的化学兼容性和共振干扰问题。然而，仪器因素，包括 NMR 管的质量，必须保持一致。任何偏差都将影响结果的准确性。本文报道了一种创新的 qNMR 方法，该方法利用内标物和外标品共同充当传统内标 qNMR 方法中所用标准品的角色。在这种新方法中，内标物只需与分析物或外标品具有化学兼容性且不存在共振干扰即可，而外标品只需具有已知的纯度。只要向外标品和分析物中添加相同数量的内标物，就无需知道内标物的确切纯度或浓度。新方法显著减轻了为每个分析物寻找合适标准品的负担。因此，qNMR 纯度测定的效率提高了，同时保留了内标法的精度。
