Colorimetric determination of silica

Umezaki, Y. and Shigen Gijutsu Shikenjo, K., Colorimetric determination of silica in the presence of, large quantities of phosphate. A silicomolybdate method, Nippon Kagaku Zasshi (1961),... 

Govett, G. J., 1961. Critical factors in the colorimetric determination of silica. Anal. Chim. Acta 25 69. 

Figure 8. Colorimetric determination of site isolation in 3-aminopropyl functionalized mesoporous silica by complexation to copper ions [22].

The chloride was added as an interference in the nitrate determination and the pH was adjusted to 1.5 with sulfuric acid to preserve the samples. In the determination of silica, the participants were to analyze the samples by either the colorimetric molybdosilicate method or the heteropoly blue method. Phosphates were to have been determined by... 

Coleman, C.J., Whitaker, M.J., Young, J.E., Lascola, R., Sanders, M.A., and Wilmarth, W.R., Remote determination of silica in highly radioactive defense waste salt solutions by the molyb-dosilicate colorimetric method. Abstracts of Papers, 223rd ACS National Meeting, April 7-11, 2002, Orlando, PL. 

Various highly refined instrumental techniques such as X-ray diffraction, optical, electron optical, infrared spectroscopy, and thermal methods are currently used for the identification and determination of the crystalline polymorphs of silica. Efficient determination of the noncrystalline forms involves wet chemical methods similar to those used for the determination of silica in natural waters and in the soil solution. Numerous procedures have been proposed for the quantitative estimation of silica in solution, and their varying efficiency may account for some of the apparent discrepancies recorded in the literature concerning soluble silica. Colorimetric methods are favored for the determination of small amounts of silica and are based upon the formation and properties of a- and j8-silicomolybdates first studied by Strickland... 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

This method was developed as a second independent method to complement the usual colorimetric procedure in the determination of a certified concentration of dissolved silica in a seawater reference material. Ion exclusion affords a separation of the dissolved silica not only from major seawater cations but also from potentially interfering anions. The detection unit limit, conservatively estimated at 2.3 ng/g Si (0.08. im), is superior to that achievable by direct analysis using inductively coupled plasma emission spectrometry. 

Various methods for the determination of silicon, particularly from biological samples are available. The techniques usually involve decomposition of the compound to give silica or a silicate by either wet combustion or fusion with sodium peroxide. The silicate formed can then be determined colorimetrically, volumetrically, or gravimetrically. Acidified ammonium heptamolybdate reacts only with monomeric Si(OH)4 and not its oligomers to give a yellow sihcomolybdic acid complex that can be determined spectrophotometrically. This method works... 

Different types of buffers at the same ionic strength and wpH can have a significant impact on the dissolution of silica. The dissolution of silica is usually measured by the silicomolybdate colorimetric method [41]. When determining the bonded-phase stability using different run buffers (effect of buffer counteranion or countercation), the same H must be used. The H values (pH of the mobile phase aqueous -i- organic) may be different from the aqueous portion of the mobile phase and may obscure if the dissolution of the silica is directly related to the type of anion/cation and/or the pH. Generally, with the addition of organic solvents the pH of the mobile phase decreases for basic buffers and increases for acidic buffers (see Section 4.5 for more details). 

The hydrolysis of sulfacetamide solution has been studied colorimetrically after separation of the degradation products on silica gel with acetone-methanol-diethylamine (90 10 10) as solvent system (56). The method has a low precision with a coefficient of variation of about 7%. Sulfanilamide, in degraded sulfacetamide formulations, has been separated by TLC followed by spectrophotometric determination of the eluted component (91). 

Figure 10. Linearity of Kubelka-Munk function with surface loading of [Co(neo)]. Transmittance values were obtained from diffuse reflectance UV-vis spectra taken at 654 nm. Data are shown for low loadings of [Co(neo)] on Merck silica grade 9385 and the values were converted to Kubelka-Munk units. Transmittance values < 5% were not used. The concentration of Co was determined by removal of the adsorbed complex by treatment with 1M HCl followed by colorimetric determination with ammonium thiocyanate. [Adapted from (57).]...

Levarato has developed a series of quantitative methods for the determination of prednisolone along other corticoids after extraction from preparations and separation by TLC on silica gel plates and determination by spectrophotometric (absorption at 240 nm) or colorimetric methods (INH-hydrazone formation, tetrazolium reaction) (81). A simple, fast and quantitative TLC-method for the determination of prednisolone in tablets is described. The method is stability-indicating with respect to accuracy, specificity, sensitivity and precision. The coefficient of variation was between 1.26 and 1.96 % and the sensitivity was about 25 ng. The chromatographic separation was performed on a silicagel plate using two step development of the plate (82). A simple TLC method of separation of prednisolone from other corticosteroids is reported (83). Prednisolone and the dephosphorylated D-homosteroid can be separated on silanised silica gel TLC plates (36). 

Strohecker [97] has worked out a procedure for quantitative determination of ascorbyl palmitate in oils and fats he oxidises with 2,6-dichlorophenol-indophenol and treats the reaction product with 2,4-dinitrophenylhydrazine. The 2,4-dinitroosazone of ascorbic acid is formed under these conditions and may be easily separated from other compounds containing phenolic groups such as tocopherols. He uses a silica gel H layer and chloroform-ethyl acetate (50 + 50) for TLC. After development, the brick red zone of the osazone is scraped off and determined colorimetrically in solution m sulphuric acid. Down to 0.001% of ascorbyl palmitate in antioxidant mixtures and in oils and fats can be determined with this procedure. 

Several months are required to acid clean the scale from the evaporators thus leaving the evaporators unavailable to perform an important process fimction. To help predict the rate of scale formation, salt solutions that feed the evaporators are analyzed for silica. The molybdosilicate colorimetric method for silica was developed for remote determination by using fiber optics to couple the light source and photodiode array spectrophotometer outside the shielded cell to the flow cell inside the cell. This remote method has considerable advantages in terms of speed and minimizing radiation dose to personnel versus analyzing the high radiation samples outside the shielded cell. 

Sodium dodecyl sulfate present in hydrophilic ointments has been determined by TLC on silica gel with flame ionization detection, which was considered better than the colorimetric method. TLC is preferred to HPLC in this case due to the low sensitivity of the refractive index detector that makes difficult the analysis of small amounts of sodium dodecyl sulfate [284]. 

Spherical rollers were machined from AISI 52100 steel, hardened to a Rockwell hardness of Rc 60 and manually polished with diamond paste to RMS surface roughness of 5 nm. Two glass disks with a different thickness of the silica spacer layer are used. For thin film colorimetric interferometry, a spacer layer about 190 nm thick is employed whereas FECO interferometry requires a thicker spacer layer, approximately 500 nm. In both cases, the layer was deposited by the reactive electron beam evaporation process and it covers the entire underside of the glass disk with the exception of a narrow radial strip. The refractive index of the spacer layer was determined by reflection spectroscopy and its value for a wavelength of 550 nm is 1.47. 

Biogenic silicon (BSI) was determined, with minor modifications, by the method of DeMaster (17). As adapted, the technique involved time-course leaching of <20-mg samples of particulate matter in 30 mL of 1.0% Na2C03 in a water bath at 85 °C. Silica in leachates was quantified either colorimetrically (Technicon autoanalyzer procedure) or by nitrous oxide flame atomic absorption. A high-temperature catalytic-combustion technique (Perkin Elmer 240C) was used for particulate organic carbon determinations. Particulate inorganic (carbonate) carbon was measured on the same instrument by CO 2 evolution after treatment of the particles with phosphoric acid. 

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