Spectrofluorimetric Determination of Alendronate by Conjugation with the Rhodamine B Sulfonyl Group

The method involving the use of the highly active chromophore, RBSC group, as the conjugation agent is useful for analyzing alendronate, and limit of detection (LOD)/LOQ values suggest that RBSC is about 8 times more sensitive than the FCS NadDPA-2Zn²⁺. The efficacy of the FCS method depends on the degree of binding and the binding constant (K_a) because the electrostatic attraction between alendronate and NadDPA-2Zn²⁺ is weak. K_a is affected by several conditions in the sample solution, such as temperature, pH and presence of competing molecules. Moreover, the fluorescence sensitivity of NadDPA-2Zn²⁺ is not sufficient because of its low extinction coefficient. In contrast, the conjugation between alendronate and RBSC does not have these limitations. Furthermore, higher sensitivity (detection limit, < 1 ng/mL) can be expected if a chromophore group with greater fluorescent activity is used for conjugation with alendronate. Alendronate, one of the bisphosphonate group of drugs, is used in the treatment of bone metastasis and several bone disorders, such as Paget's disease and osteoporosis, in post-menopausal women and older people. Generally, because the concentrations of alendronate in the therapeutic range are very low for intravenous and transdermal administration, its quantitative estimation is quite difficult