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A Novel Approach in the Structure Determination of an Impurity in the Presence of a Pharmaceutical Compound

Volume 44, Number 2 (Feb. 1990) Page 175-183

Cholli, Ashok L.; Rafalko, P. White; Ezell, E.F.; Kosarych, Z.; Ellgren, A.J.


There are several techniques and methods used to quantify the presence of low-level impurities in pharmaceutical compounds. At present it is a difficult task to determine their molecular structure unless the impurity is isolated from the pharmaceutical compound. A procedure, based on crystallization and nuclear magnetic resonance (NMR) analysis, is described for determining the molecular structure and concentration of an impurity in the presence of pharmaceutical compound, even though that impurity has not been isolated. Slow crystallization is done in order to enrich the impurity concentration to usable levels in either the solution or in some extracted powder or crystallites. High-resolution one- and two-dimensional NMR analysis of the original and enriched materials may then allow determination of the impurity's structure and its concentration in the original sample. A specific example illustrating the technique is described.