Oxidation of Isoniazid by Quinolinium Dichromate in an Aqueous Acid Medium and Kinetic Determination of Isoniazid in Pure and Pharmaceutical Formulations

Design of an optical sensor for indirect determination of isoniazid

The characterization of an optical sensor membrane is described for indirect determination of isoniazid. The sensing membrane was consisted of immobilized 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) on a triacetylcellulose membrane. The procedure is based on the reaction of Fe(III) with isoniazid in the presence of PDT. Fe(III) is reduced by isoniazid to Fe(II) which forms a complex with PDT. The complex shows an absorption maximum at 558nm. By measuring the absorbance of the complex at this wavelength, isoniazid can be determined in the range of 0.62-6.15microgmL(-1). This method was applied to the determination of isoniazid in pharmaceutical formulation and enabled the determination of isoniazid in microgram quantities.

Control of Carboxylic Acid and Ester Groups on Chromium (VI) Binding to Functionalized Silica/Water Interfaces Studied by Second Harmonic Generation

Resonantly enhanced surface second harmonic generation (SHG) measurements carried out at pH 7 and room temperature were performed to study how surface-bound carboxylic acid and methyl ester functional groups control the interaction of chromate ions with fused silica/water interfaces. These functional groups were chosen because of their high abundance in humic and fulvic acids and related biopolymers commonly found in soils. They were anchored to the silica surface using organosilane chemistry to avoid competing complexation processes in the aqueous solution as well as competitive adsorption of the organic compounds and chromate. The SHG experiments were carried out at room temperature and pH 7 while using environmentally representative chromate concentrations ranging from 1 x10(-6) to 2 x 10(-4) M. Chromate is found to bind to the acid- and ester-functionalized silica/water interfaces in a reversible fashion. In contrast to the plain silica/water interface, chromate binding studies performed on the functionalized silica/water interfaces show S-shaped adsorption isotherms that can be modeled using the Frumkin-Fowler-Guggenheim (FFG) model. This model predicts a coverage-dependent binding constant of K(ads) x exp(gtheta). Values for g are found to be 3.2(2), 2.1(2), and 1.3(2) for the carboxylic acid-, the ester-, and the nonfunctionalized silica/water interfaces, respectively, and are consistent with stabilizing lateral adsorbate-adsorbate interactions among the Cr(VI) species adsorbed to the functionalized surfaces. The FFG model allows for the parametrization of the solid-liquid partition coefficient and chromate retardation factors in silica-rich soil particles whose surfaces contain organic adlayers rich in carboxylic acid and methyl ester groups. The straightforward model presented here predicts that chromate retardation increases by up to 200% when carboxylic acid functional groups are present at the silica/water interface. Increases up to 50% are predicted for methyl ester-containing organic adlayers, and the retardation factor remains effectively near unity for the plain silica/water interface (no siloxanes present).