Abstract

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, <i>even though that impurity has not been isolated.</i> 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.

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