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Published on: January 7, 2019
Replacing Ecologically Risky Trifluoroacetic Acid and Acetonitrile With Methanesulfonic Acid and Dimethyl Carbonate
Franziska Pögel Neé Steinicke1, Taha B El-Jourani1,2, Jana Haegner1,2
1Institute of Medicinal and Pharmaceutical Chemistry, Technische Universität Braunschweig, Braunschweig, Germany.
Abstract:
It has long been recognised that, in the long term, hazardous acetonitrile (ACN) as a mobile-phase component and the environmentally critical trifluoroacetic acid (TFA) as an ion-pairing reagent should be replaced in high-performance liquid chromatography (HPLC). Nevertheless, methods relying on precisely these reagents are still widely used. Herein, we show that alternative approaches for the analysis of small molecule drugs are readily applicable, using examples from pharmaceutical quality control and medicinal chemistry. First, the principles of green analytical chemistry were implemented in an alternative HPLC method for the theophylline monohydrate monograph of the European Pharmacopoeia, without altering the core methodology. Among the various conditions tested, the use of 2% dimethyl carbonate (DMC) provided equivalent separation and an even slightly improved resolution compared with the original ACN-based pharmacopoeial method. In a second approach, we present a highly sustainable gradient HPLC method for routine purity analysis of synthesis products by replacing TFA with safe, biodegradable, and environmentally benign methanesulfonic acid (MSA). Furthermore, in the case of this gradient method, ACN could be replaced by the biodegradable and environmentally friendly DMC. An eluent composition consisting of 42 parts DMC, 23 parts EtOH, 35 parts H2O and 0.1 parts MSA was found to be equivalent to ACN containing 0.1% TFA. By employing a reproducible protocol using EtOH as a co-solvent, we were able to overcome current challenges associated with the use of organic carbonates in HPLC, which primarily arise from their limited miscibility with water. Given the continued widespread use of gradient HPLC methods employing ACN as an eluent and TFA as an acidic modifier, the methods presented herein offer significant potential to advance the implementation of sustainability in pharmaceutical quality control and medicinal chemistry.
