Semi-quantitative evaluation of small organic molecules content in amorphous calcium phosphate

A semi-quantitative UV visible spectroscopy (UV-Vis) method for detecting small organic molecules (SOM) in amorphous calcium phosphate (ACP) is presented. Although SOM, such as citric acid and glutamic acid, are widely used during calcium phosphate synthesis to modulate their properties and enhance bioactivity, their quantification has not been previously reported. In this study, ACP containing SOM (citric acid, itaconic acid and ascorbic acid) were synthesized, dissolved in 1 M orthophosphoric acid, and analyzed by UV spectroscopy. Distinct absorption maxima (λ_max) were observed: 200 nm for itaconic acid, 209 nm for citric acid, and 244 nm for ascorbic acid within the ACP matrix, aligning with those of the corresponding individual standards. Quantification revealed significant variations in SOM content of ACP matrix, with citric acid showing the highest amount (16%), followed by ascorbic acid (1.23%) and itaconic acid (0.3%). These differences are attributed to variations in their chemical structure, reactivity, and interaction with calcium phosphate. This simple and reliable approach not only provides insights into SOM concentration in ACP's but also lays the foundation for extending this technique to other calcium phosphate phases, such as octacalcium phosphate (OCP) and hydroxyapatite (HAp), thereby advancing material characterization and optimization for bone tissue engineering.