Silica colorimetric determination

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

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).]...

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),... 

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... 

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

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. 

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. 

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. 

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). 

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... 

Immediately after drying, 20 g. of unpulverized silica gel, prepared by the method presented in 3 below, is shaken for 48 hours with 400 ml. of double-distilled water. Upon contact with water and with agitation, the gel crumbles Into small granules. Finally it is filtered by means of an ultrafilter. The filtrate contains orthosilicic acid, the concentration of which can be determined either colorimetrically or by evaporation. The initial concentration in a solution prepared in this manner is generally between 12 and 15 mg. SiOg/lOO ml. This is diluted to 10 mg. SiOs/lOO ml. The filtration residue may be reused after drying at 80°C for 24 hours. 

Crystalline silica in the air may be determined by x-ray diffraction, colorimetric or IR spectrophotometric techniques (NIOSH 1984, Methods 7500,7601, and 7602, respectively). 

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). 

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