Abstract
A method for peak shape analysis and deconvolution of overlapping endotherms in differential scanning calorimetry (DSC) data is presented. The method employed a commercial computer program (PeakFit ®), which fits the experimental data to two (or more) overlapping distribution functions in which heat flux is the dependent variable and temperature is the independent variable. The endotherms were found to have either Gaussian or exponentially modified Gaussian distributions. In the examples given here, a very pure reference material, benzoic acid, and a slightly impure (99.9%) sample of (±)-ephedrine hydrochloride gave single Gaussian peak shapes, whereas a slightly impure (99.9%) sample of (1 R,2 S)-(−)-ephedrine hydrochloride displayed a single exponentially modified Gaussian peak. Binary mixtures of (1 S,2 R)-(+)- and (1 R,2 S)-(−)-ephedrine hydrochloride gave two overlapping peaks, both of which had exponentially modified Gaussian distributions. Deconvolution of these overlapping peaks allowed construction of a solid-liquid phase diagram based on their enthalpies of fusion. This phase diagram consisted of linear plots which are easily interpolated or extrapolated. Detection of one isomer in the presence of a large excess of the other by DSC was possible for compositions containing 1.5 mol% of the minor component.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.