The reactions between Phosphomolybdic acid (PMA) and Etamsylate (ETM) to form molybdenum blue (Mo⁵⁺) (Method A) and Fluconazole (FL) to form an ion associate (Method B) were investigated in terms of stoichiometry both mathematically and chemically. Mathematical characterization of the formed adducts was done using the algorithm proposed by Benesi –Hildebrand (B-H) and sis modifications Values of both the formation constant K (Lmol^-1), and molar extinction coefficient £( Lmo^1-cm^-1 ) were determined using modified B-H'' Rose-Drago'' equation. A molar ratio of (1:2) (Drug: Reagent) was detected applying the mole ratio method applying both methods. Further investigations using B-H equation for (1:1 molar ratio) or'' Rose-Drago '' (for other molar ratios) confirmed the results obtained using the mole ratio method. The obtained values for £^AD and K were 1.86 x 10⁶ L.mol.cm^-1 and 26.1x10¹¹ L.mol^-1 (Method A) and 3. 6 x 10³ and 9.36 x 10⁶ (Method B) respectively.