During related substance analysis of montelukast bulk drug, a potential unknown impurity was detected in routine reverse phase impurity profiles by high performance liquid chromatography (HPLC).

The formation kinetics of ferroin is studied under varied acid conditions at 25 • C and fixed ionic strength (0.48 mol dm −3 ) under pseudo-first-order conditions with respect to Fe 2+ by using the stopped-flow technique. The reaction followed is first and third order with respect to Fe 2+ and 1,10-phenanthroline (phen) T , respectively. Increasing the acid concentration retarded the reaction, and the reaction rate showed a positive salt effect. The rate-limiting step involved the complexation of the phen or protonated phen with [Fe(phen) complex ion. Simulated curves for the acid variation experiments agreed well with the corresponding experimental curves and the estimated rate coefficients supporting the proposed mechanism. Relatively low energy of activation (26 kJ mol −1 ) and high negative entropy of activation (−159.8 J K −1 mol −1 ) agree with the proposed mechanism and the formation of compact octahedral complex ion. C 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 515-523, 2008

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With thiocyanate, zinc(II), cobalt(II) and copper(II) ions form stable anion, [M(SCN)4] 2-. This anion in turn with methylene blue (MB +) forms ion-pair of the type MB2[M(SCN)4] and turns methylene blue to violet. The stoichiometry and stability constants of the ion-association complexes were determined using Benesi-Hildebrand method and the stoichiometry was confirmed by Job's continuous variation method. The kinetics of formation of ternary complexes was studied using stopped-flow technique. The equilibrium studies showed that the stability of ternary complexes increased in the order Co(II) > Cu(II) > Zn(II) and the formation rate constants increased in the order, Cu(II) > Zn(II) > Co(II). The relative stabilities indicate that cobalt is preferred to other two metals in the speciation of ternary complexes comparable with similar complexes in biosystems. This study also provides a method for the spectrophotometric determination of Co(II) and Zn(II) ions at nanogram levels at 25 o C and an ionic strength of 0.15 M.