New method for low molecular weight heparin quantification in tablets by suppressed conductivity detection and cryptand column

Unfractioned Heparins (UFH) and Low Molecular Weight Heparins (LMWHs) are non-chromophoric, high charged sulphated molecules which are difficult to elute and detect with conventional liquid chromatography methods. Moreover, the detection of LMWHs at low concentration level, like in samples coming from dissolution test of tablets formulated with Heparins is problematic due to the weak response by UV or refractive index detection. According to the European Pharmacopoeia requirements, the assay of LMWHs is based on the anti-Xa activity and anti-IIa activity factors, which are biological parameters related to the antithrombotic activity of this compound family. The same assay method could also be applied to determine the dissolution rate of LMWHs contained in tablets, but it is time consuming and expensive test. The challenge was to develop a simpler and faster alternative method based on Ion Chromatography coupled with Suppressed Conductivity detection, but the particular polycharge interaction of LMWHs with anions exchanger makes the analyte with standard eluents and columns difficult to elute . The analytical problem could be solved by using a particular chromatographic phase with 2,2,2 cryptand sites which gives variable capacity in anion exchange depending on the used eluent. Such phase was very effective for the elution of strongly retained polyanions using simple inorganic eluent phase suitable for suppressed conductivity detection as well. The developed method allows the elution of a unique peak, which represents the whole polymeric distribution, and therefore it makes easy to quantify quickly and selectively the active ingredient in case of multiple analysis like when a dissolution test is required to characterize and discriminate between different tablets formulations. The method was tested and developed in Cosmo Pharmaceuticals QC labs and the validation results are reported in the present paper. Besides, a comparison between biological and chromatographic methods was carried out as well.