Effect of time and storing conditions on iron forms in ferrous gluconate and Ascofer

Antianemic medicament Ascofer and ferrous gluconate, its basic iron bearing ingredient, were studied with the use of Mossbauer spectroscopy. Room temperature spectra gave a clear evidence that two phases of iron were present viz. ferrous (Fe2+) as a major one with a contribution of 85+-5%, and ferric (Fe3+) whose contribution was found to be 15+-5%. However, the actual values of the contributions of the two kind of the iron ions in Ascofer depend on sample’s age: the abundance of Fe2+ ions increases with time by 10% after 51 months, while that of Fe3+ decreases by the same amount. This means that an internal reduction of Fe3+ ions takes place. Ferrous ions were shown to occupy at least two different sites. In Ascofer, the relative abundance of the two sites does not depend on the age of sample, while in the gluconate the population of site 1 increases and that of site 2 decreases with the age of the sample.

💡 Research Summary

The study employed ⁵⁷Fe Mössbauer spectroscopy to investigate the oxidation state and site distribution of iron in the antianemic tablet Ascofer and its principal active ingredient, ferrous gluconate. Spectra recorded at ambient temperature revealed two distinct iron components: a dominant ferrous (Fe²⁺) phase accounting for 85 ± 5 % of the total iron and a minor ferric (Fe³⁺) phase comprising 15 ± 5 %. By analysing samples stored for various periods (0, 12, 24, 36, and 51 months) under controlled room‑temperature conditions, the authors observed a systematic shift in the Fe²⁺/Fe³⁺ ratio. After 51 months, the Fe²⁺ fraction increased by roughly 10 percentage points, while the Fe³⁺ fraction decreased by the same amount, indicating an internal reduction of Fe³⁺ to Fe²⁺ that occurs without external reagents.

Further spectral deconvolution showed that Fe²⁺ occupies at least two crystallographically distinct sites. In the commercial formulation Ascofer, the relative populations of these two sites remained essentially constant over the entire ageing period, suggesting that excipients (e.g., vitamin C, sugars, coating agents) stabilize the local coordination environment and prevent site redistribution. By contrast, in pure ferrous gluconate the population of site 1 grew with age while that of site 2 declined, implying a slow re‑organisation of the gluconate lattice or a gradual migration of Fe²⁺ to a more thermodynamically favourable coordination sphere during storage.

The findings have several practical implications. First, the increase in Fe²⁺ content over time could enhance the bioavailability of the product, because ferrous iron is more readily absorbed in the gastrointestinal tract than ferric iron. Second, the stability of site distribution in Ascofer underscores the importance of formulation design; appropriate choice of stabilising excipients can lock iron into a favorable coordination environment, thereby preserving therapeutic potency throughout the product’s shelf‑life. Third, Mössbauer spectroscopy proved to be a highly sensitive tool for detecting subtle changes in iron oxidation state that conventional bulk analytical techniques (e.g., ICP‑AES, titration) might miss, highlighting its value for quality‑control laboratories.

Nevertheless, the study is limited to ambient‑temperature storage. Real‑world conditions often involve elevated temperature, humidity, and light exposure, which could accelerate oxidation rather than reduction. Moreover, Mössbauer spectroscopy provides an averaged picture of the iron environment and cannot resolve nanoscale heterogeneities or amorphous phases. Future work should therefore combine complementary techniques such as X‑ray diffraction, FT‑IR, and electron microscopy to map structural evolution, and should include in‑vitro or in‑vivo absorption studies to directly correlate the observed Fe²⁺/Fe³⁺ shifts with pharmacokinetic outcomes.

In summary, the paper demonstrates that both Ascofer tablets and ferrous gluconate powders undergo an internal redox transition during long‑term storage, with Fe³⁺ gradually converting to Fe²⁺. While the commercial tablet maintains a stable distribution of ferrous sites, the pure gluconate exhibits a redistribution that reflects lattice relaxation. These insights contribute to a deeper understanding of iron‑based supplement stability, inform optimal storage recommendations, and suggest formulation strategies to preserve the desired ferrous state for maximal therapeutic efficacy.