Abstract:

The sulfate ester groups of low molecular weight heparins (LMWHs) are labile and easily hydrolyzed to produce free sulfate ions during the process of manufacture and storage. In addition, other anions such as chloride and acetylate are often introduced in the products. For monitoring the stability of the products, ion chromatography is the commonly used technique for determining the free anions in LMWHs. However, the column and the suppressor of ion chromatography are easily contaminated by LMWHs due to their relatively large molecules. Therefore, we developed a capillary electrophoresis (CE) method with indirect ultraviolet (UV) detection for determining the free anions in LMWHs, including sulfate, chloride, fluoride, phosphate and acetate. Unlike the commonly used anion separation CE method which uses chromate as the background absorption electrolyte, phthalate was used as the probe anion because its electrophoretic mobility matches better to all of the anions than chromate so that more narrow peaks could be obtained. Moreover, the molar absorptivity of phthalate at 230 nm (4754 L/(mol·cm)) was higher than that of chromate at 254 nm (2400 L/(mol·cm)). The combination of the narrow peak shape with the high molar absorptivity of the probe ion improves the detection sensitivity nearly to the lever of ion chromatography. Effects of various CE parameters on the separation of the anions were investigated and optimized. The method displayed excellent linearity in the concentration range from 0.002 to 1 mmol/L. The relative standard deviations (RSDs) for intraday (n=6) and interday (n=3) repeatabilities in terms of migration times and peak areas were all less than 3%. The limits of detection (S/N=3) and limits of quantitation (S/N=10) were determined as 0.4-0.8 μmol/L and 2-4 μmol/L for the above anions, respectively. The method was successfully applied for the stability monitoring of LMWHs.

Key words: anions analysis, capillary electrophoresis (CE), low molecular weight heparin (LMWHs), stability monitoring