Quantifying Total, Bound and Free Dextran in Iron Dextran: A Multi-Method Approach with Dialysis, Gel Filtration Chromatography and HPLC

Conventional carbohydrate assays often fail to distinguish between dextran that is free in solution and dextran that is covalently or coordinatively bound to iron. Therefore, a multi-method analytical strategy is needed to selectively quantify both fractions. In this study, we developed and validated an approach combining dialysis-based ultrafiltration, gel permeation chromatography (GPC), and high-performance liquid chromatography (HPLC) with refractive index (RI) detection to separate, identify, and quantify free and bound dextran in an Iron Dextran formulation. This method enables comprehensive dextran profiling and supports regulatory-compliant characterization of complex injectable products. Materials and Methods: In first step bound and free dextran was separated from Iron dextran using ultracentrifugal filters with a 10kDa molecular weight cutoff. The separation was monitored by gel permeation chromatography (GPC) using Ultrahydrogel columns (1000Å and 120Å, 7.8mm x 300mm I.D., 12μm particle size) connected in series. The mobile phase consisted of 40mM sodium phosphate buffer (pH 7.0) with 0.02% sodium azide, and detection was performed using a refractive index (RI) detector at a flow rate of 0.5mL/min. In second step Total and bound dextran were hydrolysed to yield glucose, which was then quantified using a validated reverse-phase high-performance liquid chromatography (RP-HPLC) method. The RP-HPLC analysis was performed on a SUGAR SH1011 column (8.0 x 300mm I.D., 6 μm particle size) using water as the mobile phase at a flow rate of 0.6mL/min, with RI detection. Conclusion: This integrated methodology enables the selective and quantitative determination of bound and free dextran components in Iron Dextran formulations. The results showed total dextran content of 60-70%, with 14-18% bound to the iron core and 40-50% in the free form. The synergy of these methods provides a comprehensive understanding of iron dextran's complex structure, highlighting the value of a multi-method approach in pharmaceutical analysis.