Capillary Electrophoretic Determination of Gatifloxacin from Pharmaceutical Preparation

Capillary zone electrophoresis has been used for the determination of gatifloxacin from its pharmaceutical preparation (tablets), using fused silica capillary. Separation was performed after hydrodynamic injection; the separation was achieved by applying 21 Kv voltage. Phosphate buffer solution (pH 9.5) was used as separation electrolyte. Detection was at 280 nm using a UV- detector. Under these experimental conditions the analysis takes 8 min. A linearity range for gatifloxacin was between 20.0 g mL^–1 to 60.0 g mL^–1. The method was validated and was found to be specific, precise, accurate, reproducible and robust and can be applied for the routine analysis of gatifloxacin from formulation and bulk drug.     

Radiometric,potentiometric and conductometric measurements of the solubility and solubility product of europium trifluoride

The solubility and solubility product of europium trifluoride were measured by radiometric, potentiometric and conductometric methods. There are significant differences in the values of both solubility and solubility product obtained by the three different techniques. Due to reasons discussed in the text, radiometric values seem to be more acceptable than the others. The thermodynamic functions such as ΔH⁰, ΔG⁰ and ΔS⁰ for the dissolution process were also measured. The positive values of ΔH⁰ and ΔG⁰ and the negative value of ΔS⁰ are indicative of the slight solubility of EuF₃. The dependence of solubility on pH and also on the fluoride concentration has also been studied. It was confirmed that europium forms a monofoluoride complex in aqueous solution. The stability constant of this complex was estimated.     

Quantitative evaluation of Lewis acidity of metal ions with different ligands and counterions in relation to the promoting effects of Lewis acids on electron transfer reduction of oxygen

The g(zz) values of ESR spectra of superoxide (O(2)(.-) complexes of metal ion salts acting as Lewis acids with different ligands and counterions were determined in acetonitrile at 143 K. The binding energies (DeltaE) of (O(2)(.-)/Lewis acid complexes have been evaluated from deviation of the g(zz) values from the free spin value. The DeltaE value is quite sensitive to the difference in the counterions and ligands of metal ion salts acting as Lewis acids. On the other hand, the fluorescence maxima of the singlet excited states of 10-methylacridone/Lewis acid complexes are red-shifted as compared with that of 10-methylacridone, and the relative emission energies (Deltahnu(f)) vary significantly depending on the Lewis acidity of metal ion salts with different counterions and ligands. The promoting effects of Lewis acids were also examined on electron transfer from cobalt(II) tetraphenylporphyrin to oxygen in acetonitrile at 298 K, which does not occur in the absence of Lewis acids under otherwise the same experimental conditions. Both DeltaE and Deltahnu(f) values are well correlated with the promoting effects of Lewis acids on the electron transfer reduction of oxygen. Such correlations indicate that DeltaE and Deltahnu(f) values can be used as quantitative measures of Lewis acidity of metal ion salts with different ligands and counterions. The Lewis acidity thus determined can also be applied to predict the promoting effects of Lewis acids on organic synthesis.     

Enhancement of H2- and retardation of O2-adsorption during O2?H2 titration cycles on Pt?Al2O3 catalyst surfaces

The title effects can be eliminated if the slow bleeding of H₂ from freshly reduced CuO-towers (often used as O₂-getters in purifying N₂ carrier gas) can be avoided, then H₂–O₂ titrations of Pt surfaces give consistent values from almost the first titration. Water injected at 25 °C also hardly affects the titer values.

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H₂ O₂ , H₂ CuO ( O₂ N₂ — -). H₂–O₂ Pt . , 25° C, .

     

Simultaneous RP-LC Determination of Losartan Potassium, Ramipril, and Hydrochlorothiazide in Pharmaceutical Preparations

A simple, rapid, and precise reversed-phase high-performance liquid chromatographic method has been developed for simultaneous determination of losartan potassium, ramipril, and hydrochlorothiazide. The three drugs were separated on a 150 mm × 4.6 mm i.d., 5 μm particle, Cosmosil C₁₈ column. The mobile phase was 0.025 m sodium perchlorate–acetonitrile, 62:38 (v/v), containing 0.1% heptanesulphonic acid, pH adjusted to 2.85 with orthophosphoric acid, at a flow rate of 1.0 mL min⁻¹. UV detection was performed at 215 nm. The method was validated for linearity, accuracy, precision, and limit of quantitation. Linearity, accuracy, and precision were acceptable in the ranges 35–65 μg mL⁻¹ for losartan, 1.75–3.25 μg mL⁻¹ for ramipril, and 8.75–16.25 μg mL⁻¹ for hydrochlorothiazide.     

A kinetic study of the displacement reaction between nickel(II) and zinc-ethylenediaminetetraacetate by a radiometric method

A radiometric study of the kinetics of the displacement reaction between nickel(II) and⁶⁵Zn-labeled zinc salt of ethylenediaminetetraacetic acid, which was previously used by the authors for the analysis of trace quantities of nickel, has been carried out under varying conditions of temperature, pH etc. The above reaction was confirmed to be first order with respect to both Ni²⁺ and to^*ZnEDTA. The overall reaction rate constant, k_f, has been shown to be inversely proportional to the concentration of Zn²⁺ and directly proportional to the concentration of H⁺. From the dependence of the rate constant on the concentration of Zn²⁺ and H⁺ a three-step mechanism is proposed for the above reaction. The values for E_a, ΔH^‡, ΔG^‡ and ΔS^‡ for the overall reaction have been computed from the experimental data.     

Sequential liquid-liquid extraction graphite furnace atomic absorption spectrometric (GFAAS) and spectrophotometric determination of zirconium(IV) with calixarene hydroxamic acid

A new calixarene hydroxamic acid, 25,26,27,28-tetrahydroxy-5,11,17,23-tetrakis (N-p-chlorophenyl) calix[4]arene hydroxamic acid (CPCHA) is synthesized and used for the extraction and graphite furnace atomic absorption determination of zirconium(IV). The extract is also determined spectrophotometrically as CPCHA-SCN complex having maximum absorbance at 447 nm with molar absorptivity 9.4x10(3) l mol(-1) cm(-1). The Beer's law obeys in the range of 1.0-9.5 ppm of zirconium. The graphite atomic absorption (GFAAS) increases the sensitivity by about 50 folds. The method is applied to the trace determination of zirconium(IV) in standard samples.     

Ion-exchange separation and spectrophotometric determination of vanadium in environmental samples

A selective and sensitive method for the extraction and spectrophotometric determination of vanadium(V) in microgram quantities is described. The molar absorptivity of the yellow vanadium(V)-caffeic acid-Aliquat 336 extract is 1.3 x 10(4) 1.mole(-1).cm(-1) at 370nm. The method is compared with the atomic-absorption spectrometric method and applied to the trace determination of vanadium in steel, alloys, a rock and environmental samples.