The role of solvents in the signal separation for quantitative 1H NMR spectroscopy

Compared to conventional means of quantitative drug analysis, NMR spectroscopy only provides a limited set of adjustable parameters to enhance the quality of the analysis such as pH value, temperature, auxiliary reagents, magnetic field strength or properties of the solvent. In this work we investigate the influence of the kind of solvent on the signal separation of decisive resonances in the NMR spectra of codergocrine mesilate and flupentixol dihydrochloride. Polarity and aromaticity of the solvent play a crucial role in the optimization of signal separation. However, the set of applicable solvents is usually limited due to certain boundary conditions like solubility of the agent. Therefore the effects of solubilizers as well as mixtures solvents on the chemical shift also have to be taken into account. The quantitative results obtained by means of 1H NMR spectroscopy were found to be in good agreement with the results carried out using official HPLC methods of International Pharmacopoeias.