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Alex O. Okaru [1] and Tobias S. Brunner [2] and Svenja M. Ackermann [2] and Thomas Kuballa [2] and Stephan G. Walch [2] and Matthias Kohl-Himmelseher [2] and Dirk W. Lachenmeier [2]

Academic Editor: Josep Esteve-Romero

1, Department of Pharmaceutical Chemistry, University of Nairobi, P.O. Box 19676-00202, Nairobi, Kenya, uonbi.ac.ke

2, Chemisches und Veterinäruntersuchungsamt (CVUA) Karlsruhe, Weissenburger Strasse 3, 76187 Karlsruhe, Germany, cvua-karlsruhe.de

Received May 31, 2017; Revised Aug 22, 2017; Accepted Sep 6, 2017

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

There is growing need for modern analytical techniques for analysis of fluorine-containing pharmaceutical substances including active pharmaceutical ingredients, brand and generic finished products, and also for the detection of potentially counterfeited pharmaceuticals. These new techniques are aimed not only at maximizing analytical throughput but also minimizing expenses while preserving acceptable method performance characteristics. Nuclear magnetic resonance spectroscopy (NMR) is such a technique whose scope of applications continues to expand. Indeed with the marked improvements on the sensitivity of NMR spectrometers, quantitative analytical applications have tremendously sprung up across many fields including foods, beverages [1–5], and pharmaceuticals [6]. NMR spectroscopy offers unparalleled rich information on samples, and, with rapid validated methods, high throughput can be achieved without destroying the sample [7]. Unlike the current chromatographic techniques that require reference standards, often expensive and unavailable in many laboratories, NMR spectroscopy enables quantification without necessity of a primary reference standard, thus lowering the cost of analysis [8, 9].

Traditionally, most of the NMR spectroscopic applications are based on 13C and 1H nuclides due to the relatively high abundance of carbon and hydrogen in natural compounds compared to phosphorus and fluorine. As an alternative nuclide, 19F offers the advantages of higher natural abundance compared to 13C and less risk of signal overlap compared to 1H since proton NMR shows a narrow range of the chemical shift (typically 0–10 ppm) and shows an increased spectral complexity due to coupling of neighbouring protons. Furthermore, 19F NMR has a broader chemical shift range (approx. 500 ppm) [10], which helps to avoid signal overlap and shows less interference from homonuclear coupling [11–13]...

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