Tailoring the particle size of monodispersed colloidal gold

The paper describes a convenient, rapid, and reproducible method for the synthesis of stable dispersions of uniform gold nanoparticles at ambient temperatures by mixing aqueous solutions of tetrachloroauric acid and iso-ascorbic acid. The influence of the experimental conditions on the size of the gold particles and the stability of the final sols was monitored by dynamic light scattering and UV-vis spectrophotometry. It was found that the size of the resulting nanoparticles is affected by the concentration and the pH of gold solution, while the stability of the electrostatically stabilized final sols is strongly dependent on the excess of reductant in the system, the ionic strength, and the temperature of the precipitation. Since the preparation process does not require the addition of a dispersing agent, the surface of the resulting gold nanoparticles can be easily functionalized to make them suitable for applications in medicine, biology, and catalysis.

Stabilizer-free nanosized gold sols.

The importance of vitamin C to the human body is widely acknowledged throughout the globe. The deficiency of this vitamin leads to various diseases. In view of its importance, numerous methods including spectrophotometric ones have been developed for its determination in pharmaceuticals, foods and biological samples. A comprehensive review of the available spectophotometric methods for the determination of ascorbic acid is presented.

Photometric Methods for the Determination of Vitamin C

Colorimetric Determination of Catecholamines by 2,3,5-Triphenyltetrazolium Chloride

An analytical procedure based on the reaction of nitroso-R salt with reduced iron(II) is developed for the analysis of ascorbic acid. The absorbance of the resulting green colored complex is measured at 705 nm. Beer's law is obeyed over the range 0.2–3.0 μg ml−1 ascorbic acid with a molar absorptivity of 4.5 × 104 l mol−1 cm−1. The substances commonly found with vitamin C formulations are tolerated. Some of the marketed products of ascorbic acid were analyzed by the proposed method with satisfactory results.

Nitroso-R Salt As a Sensitive Spectrophotometric Reagent For the Determination of Vitamin C

Ascorbic acid reacts with 2,3,5-triphenyltetrazolium chloride in alkaline medium giving pink color having 5μg/ml as visual limit of identification. This color reaction has been utilized for the colorinietric determination of ascorbic acid from pharmaceutical preparations in minute quantities. The maximum tolerable amount of other vitamins, sugars and organic compounds during determination of ascorbic acid is reported.

Microdetermination of ascorbic acid and tryptophan by colorimetry.

A rapid, convenient and accurate method for the determination of xanthates has been developed. N-bromosuccinimide has been used to displace iodine from potassium iodide which in turn oxidizes xanthate to dixanthogen. The pH 4 is optimum for the determination. The maximum relative standard deviation is 6% in the case of ethyl potassium xanthate when a 0.5 mg sample was taken.

Microdetermination of Xanthates

A new color reaction for the determination of gold(III) has been developed. Gold reacts with 3-methyl-4-vanillidine isoxazolone-5 in basic media at 90° to produce a pink color which is specific. Cobalt and nickel do not interfere when present upto 4 folds. Maximum tolerable amounts of other metal ions have also been studied.

Colorimetric determination of gold(III) using 3-methyl-4-vanillidine isoxazolone-5

A simple and accurate method for the determination of gold(III) by means of isonicotinic acid hydrazide is described. Interference due to metal ions, including that of silver, has been eliminated. Tolerable amounts of other metal ions which may be present have been determined.

Spectrophotometric determination of gold by isonicotinic acid hydrazide

A method for semiquantitative determination of thiourea, thiocyanate, and sulfide is described. It involves making “circular spots” or rings on chromatoplates using the circular thin layer Chromatographic apparatus. The method is based on sensitivity and specificity of spot reactions and comparison of the color intensity of a “circular spot” with that of sensitivity standards. The accuracy of the method is ± 5% and the procedure is rapid, simple and economical.

Iftikhar Ahmad

Papers

Microdetermination of ascorbic acid and tryptophan by colorimetry.

Microdetermination of Xanthates

Colorimetric determination of gold(III) using 3-methyl-4-vanillidine isoxazolone-5

Spectrophotometric determination of gold by isonicotinic acid hydrazide

Semiquantitative determination of thiourea, thiocyanate, and sulfide by circular thin layer chromatography