Abstract
A new analytical procedure, combining sample pretreatment with solid phase extraction and high performance liquid chromatography, was developed and applied to ketoprofen:cyclodextrin (CD) complexes. The significant differences in molar absorptivity between free and CD bound drugs lead to analytical errors up to 30%. Procedures routinely used to remove most of the common excipients proved to be inadequate, creating the necessity of more specific (HPLC) analytical methods including the step of dissociation and separation of drugs from CDs before the quantitation by UV detector. In the case of complexes such as Ketoprofen: CDs, strong binding to CDs inhibits the dissociation. Prior to the analysis, the addition of molecules competing the binding in the CD cavity fairly decreased the strength of the complexation. When molecules, competing the binding to CD such as 1-adamantanol, were added to the samples the results were improved. The extent of the selective binding and the drug displacement were monitored with H-NMR spectroscopy and it was revealed that only partial dissociation of the complexes was obtained. The combination of the sample pre-treatment with a solid phase extraction technique was proved to be inevitable for the dissociation of the complex. When analyzing supramolecules spectral changes, arising from intramolecular and/or intermolecular interactions, are expected. Consequently, analytical methods utilized should be carefully revised.
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