Abstract
X-ray powder diffraction (XRPD) and thermal analysis (differential scanning calorimetry/derivative of thermogravimetry (DSC/DTG)) are solid-state techniques that can be successfully used to identify and quantify various chemical compounds in polycrystalline mixtures, such as dietary supplements or drugs. In this work, 31 dietary supplements available on the Polish market that contain iron compounds, namely iron gluconate, fumarate, bisglycinate, citrate and pyrophosphate, were evaluated. The aim of the work was to identify iron compounds declared by the manufacturer as food supplements and to try to verify compliance with the manufacturer’s claims. Studies performed by X-ray and thermal analysis confirmed that crystalline iron compounds (iron (II) gluconate, iron (II) fumarate), declared by the manufacturers, were present in the investigated dietary supplements. Iron (II) bisglycinate proved to be semi-crystalline. However, depending on the composition of the formulation, it was possible to identify this compound in the tested supplements. For amorphous iron compounds (iron (III) citrate and iron (III) pyrophosphate), the diffraction pattern does not have characteristic diffraction lines. Food supplements containing crystalline iron compounds have a melting point close to the melting point of pure iron compounds. The presence of excipients was found to affect the shapes and positions of the endothermic peaks significantly. Widening of endothermic peaks and changes in their position were observed, as well as exothermic peaks indicating crystallization of amorphous compounds. Weight loss was determined for all dietary supplements tested. Analysis of the DTG curves showed that the thermal decomposition of most food supplements takes place in several steps. The results obtained by a combination of both simple, relatively fast and reliable XRPD and DSC/DTG methods are helpful in determining phase composition, pharmaceutical abnormalities or by detecting the presence of the correct polymorphic form.
Highlights
The X-ray powder diffraction (XRPD) made it possible to state that the active ingredients declared by the manufacturers in their specifications were present in the analyzed products containing crystalline and semi-crystalline iron compounds iron (III) pyrophosphate and iron (III) citrate, as amorphous substances do not give a clear diffraction pattern
differential scanning calorimetry (DSC)/DTG studies for iron (II) gluconate monohydrate and iron (II) gluconate dihydrate distinguished these hydrates and confirmed that iron (II) gluconate monohydrate was present in the tested dietary supplements
Based on the DTG curves, it can be concluded that all tested oral iron supplementation (OIS) containing iron (II) gluconate are subject to thermal decomposition in the temperature range 180–200 ◦ C
Summary
Iron is one of the essential elemental nutrients involved in many key cellular processes. Iron is responsible, for example, for oxidative damage to lipids, proteins or DNA [1]. The low-energy barrier between Fe(II)/Fe(III) oxidation states is responsible for crucial metabolic reactions, such as cellular respiration and oxygen transport, and the formation of reactive oxygen species (ROS) [2]. Iron metabolism is precisely regulated in the human body by various mechanisms. Two conditions are possible: iron overload or deficiency. Iron deficiency is a typical impact of malnutrition or parasitic infections. Iron deficiency can occur in immunocompromised patients, anticancer therapy, various chronic diseases, and the elderly [3,4,5]
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