VALIDATION OF UV-VISIBLE SPECTROPHOTOMETRIC METHOD FOR THE ANALYSIS OF PREPARED AMORPHOUS SILICA USING DEVELOPED METHOD

Abstract

Glass sand is found in abundance naturally around the sea shores. The sand used in this work is the glass sand from Igbokoda in Ondo State. Amorphous silica was produced from this sand by fluxing 45g of the acid-washed sand with 14.25g NaOH at 8400C in furnace specifically designed and developed for this work. The yield was 82.5% . Microscopic analysis of the silica showed a resolved 2-D imaging at a magnification of 200x of a particle size of 1.5um agglomerates on drying. X-ray diffraction pattern showed diffraction maxima 250 and base width between 220 and 300 (20) and the quantitative analysis of the elemental composition was done by using Energy Dispersive X-ray florescence (EDXRF) [XR – 100CR].The spectrophotometeric analysis in the visible showed wavelength of maximum absorption (λ max ) as 825+ 5nm for Silicon molybdenum blue. The UV-Visible spectrophotometer Jenway 6405 mode used was calibrated and Potassium permanganate KMnO4, was used to check the wavelength scale. Normal calibration procedure was applied to determine the linear range of 0.0 – 10mgdm-3, the sensitivity 0.0395AUmg-1dm-3 and detection limit of 0.002mgdm-3 were ascertained before the introduction of the sample. The Ringbom – Ayres plot was done to determine the precision of spectrophotometer. The plot gave an exponential graph for the plot of Transmittance Vs. Concentration and a fairly S shape with point of inflexion occurring at 37.5% Transmittance for KMn04 and 40% Transmittance for molybdenum blue complex thus obeying Beer’s law , for the plot of Transmittance Vs. logarithm of Concentration corresponding to the precision of -3.469 x 102 (230/S) for KMnO4 and -3.864 x 10-1 for molybdenum blue complex, relative error. Silicon molybdenum blue complex [SiMo4v, Mo8viO40] was prepared from acidified Ammonium molybdate tetrahydrate, [Si Mo12viO40-3] using Ascorbic acid. The spectrum of the molybdenum blue on showed a wavelength of maximum absorption (λ max ) as 825+ 5nm. The scanning gave standard results with linear range of 0.00-2.00mgdm-3, a sensitivity of 0.438 AU mg-1dm-3, Molar absorptivity of 3.540 X 10-7 AU mol-1dm-1 cm-1 and a detection limit of 0.002mgdm-3. Various compositions of standard silicon solution were used for the performance checked of the instrument. The corresponding silicon concentration of the amorphous silica sample was deduced from the calibration curve by interpolation. The method was also applied for the determination of silicon contents of some toothpaste in the market. The result from the UV-Visible spectrophotometer was compared with the result generated by X-ray spectrophotometer. Data treatment was done statistically; least Square was applied to the normal calibration graph. Computer software (Grand optimizer) was used for curve fitting. Keyword: Amorphous silica, Glass sand, Ammonium molybdate, Molybdenum blue method