A Novel Spectrophotometric Determination and Kinetic Study of Sulfamethoxazole in Pure and Tablet Formulation using 9-chloroacridine Reagent

A spectrophotometric method has been developed for analysis of Sulfamethoxazole (SMX) in pure and dosage forms. The method is based on the reaction of the SMX with 9-chloroacridine (9-CA) reagent in organic and acidic medium, to produce a yellow product having maximum absorption at 448 nm. Beer’s law was obeyed in the concentration range 1-30 μg.ml-1 with molar absorptivity of 1.63x104 L.mol-1.cm-1 with good detection and quantification limits. Accuracy (Average recovery %) and precision are 98.43% and 0.651, respectively. The proposed method was applied successfully for determination of Sulfamethoxazole in its commercial dosage form as tablet and agree well with the official method. The equilibrium constant and the thermodynamic functions (ΔHo, ΔGº and ΔSº) of the complex formation were estimated. The study revealed that the complex formation could occur spontaneously, the type of interacting forces between SMX and 9-CA are physical is nature and association increases the order of the studied systems. The results of kinetic parameters indicated that, the reaction is pseudo first order with respect to SMX. The rate constant at various temperatures and the thermodynamic functions of activation were determined. Theoretical parameters were calculated by applying the semi-empirical Austin method (AM1). These parameters are helped to suggest reaction mechanism and supporting other results.

Solubility of Sulfamethazine in the Binary Mixture of Acetonitrile + Methanol from 278.15 to 318.15 K: Measurement, Dissolution Thermodynamics, Preferential Solvation, and Correlation

Solubility of sulfamethazine (SMT) in acetonitrile (MeCN) + methanol (MeOH) cosolvents was determined at nine temperatures between 278.15 and 318.15 K. From the solubility data expressed in molar fraction, the thermodynamic functions of solution, transfer and mixing were calculated using the Gibbs and van ’t Hoff equations; on the other hand, the solubility data were modeled according to the Wilson models and NRTL. The solubility of SMT is thermo-dependent and is influenced by the solubility parameter of the cosolvent mixtures. In this case, the maximum solubility was achieved in the cosolvent mixture w0.40 at 318.15 K and the minimum in pure MeOH at 278.15 K. According to the thermodynamic functions, the SMT solution process is endothermic in addition to being favored by the entropic factor, and as for the preferential solvation parameter, SMT tends to be preferentially solvated by MeOH in all cosolvent systems; however, δx3,1<0.01, so the results are not conclusive. Finally, according to mean relative deviations (MRD%), the two models could be very useful tools for calculating the solubility of SMT in cosolvent mixtures and temperatures different from those reported in this research.

THERMODYNAMIC PROPERTIES OF THE Sb2Te3 COMPOUND

Thermodynamic properties of the Sb2Te3 compound were studied by measuring electromotive force (EMF) with a liquid electrolyte in the temperature range of 300-450 K. The partial molar functions of antimony in alloys and the corresponding standard integral thermodynamic functions of the Sb2Te3 compound were calculated for the first time based on the EMF measurements under standard conditions. Comparative analysis of obtained results with literature data was carried out

THERMODYNAMIC FUNCTIONS OF FORMATION OF LITHIUM TITANATES

By the method of electromotive forces measuring concentration chains: Pt│Li2O│ ZrO2+10 wt% Y2O3, lithium glass. (Li2O)x(TiO2)1-x│Pt in the temperature range T=1000–1200K and concentrations 0.35÷0.95 mol fraction TiO2, the thermodynamic functions of the formation of the compounds Li4TiO4, Li2TiO3, Li4Ti5O12 and phases based on Li2TiO3:Li1.92Ti1.04O3.04, Li2.12Ti0.94O2.92 were determined. With the exception of the compound Li2TiO3, the thermodynamic functions of the formation of lithium titanates are deter¬mined for the first time. The thermodynamic functions of formation are calculated for the 1200 K and for the standard state at 298 K. The thermodynamic functions of the formation of lithium titanates are determined from simple substances and from binary compounds Li2O and TiO2. In particular, for the free energy, enthalpy of formation and standard entropy we obtained: ∆G_298^0(Li4TiO4)=–2149 kJ∙mol-1; ∆G_298^0(Li2TiO3)=–1565; ∆G_298^0(Li4Ti5O12)=–5923; ∆H_298^0(Li4TiO4)=–2286 kJ∙mol-1; ∆H_298^0(Li2TiO3)=–1662; ∆H_298^0(Li4Ti5O12)=–6287; S_298^0(Li4TiO4)=119.1 J∙mol-1∙K-1; S_298^0(Li2TiO3)=84; S_298^0(Li4Ti5O12)=315.7

The low temperature heat capacity of Li2Mo0.05W0.95O4

The heat capacity of a lithium tungstate single crystal doped by 5% molybdenum Li2Mo0.05W0.95O4 in the range of 78.5–302.8 K was measured by the adiabatic method. No anomalous behavior of heat capacity was found. The heat capacity function was obtained in the range of 0–303 K by extrapolating to zero temperature and fitting experimental points. Thermodynamic functions of entropy, enthalpy increment and Gibbs free energy at 298.15 K were calculated using the obtained data.

Precise Numerical Differentiation of Thermodynamic Functions with Multicomplex Variables

The multicomplex finite-step method for numerical differentiation is an extension of the popular Squire–Trapp method, which uses complex arithmetics to compute first-order derivatives with almost machine precision. In contrast to this, the multicomplex method can be applied to higher-order derivatives. Furthermore, it can be applied to functions of more than one variable and obtain mixed derivatives. It is possible to compute various derivatives at the same time. This work demonstrates the numerical differentiation with multicomplex variables for some thermodynamic problems. The method can be easily implemented into existing computer programs, applied to equations of state of arbitrary complexity, and achieves almost machine precision for the derivatives. Alternative methods based on complex integration are discussed, too.