Silica identification

Attempts to determine the solubility of amorphous silica in salt water solutions at near neutral pH and 0 to 5 C or 22 to 25 C have yielded a wide range of values9 which results in part from aging of the silica surface in contact with solution This makes determination of an initial solubility for silica difficult. Low temperature aging in salt water solutions or seawater causes a decrease in surface area, in specific pore volxime, and in solubility. Solubilities determined at pressures to 1000 atmospheres (lx 10 pascals) indicate that aging causes an increase in density of the surface silica this data also allows calculation of the partial molal voltime of dissolved silica. Identification of specific processes involved with aging of an amorphous surface are necessary for understanding silica solubility. 

Applications The following use was made of infrared and Raman specfroseopy identification of surface groups on treated and untreated fumed silica, identification of silica functional groups and coatings by Raman spectroscopy, silane deposition on various fillers, surface grafting of barium sulfate by acryloamide grafting of wood fiber, specbal absorption of filler,crystallization of polymer in the presence of filler, absorption of polyacrylate on alumina, deformation of fibers in composites by Raman... 

Payoungkiattikun, W., Okazaki, S., Nakano, S., Ina, A., H-Kittikun, A., and Asano, Y, "In silica identification for a-amino-e-caprolactam racemases by using information of the structure and function relationship." Appl Biochem. Biotechnol, 176,1303-1314 (2015). 

Figure Bl.25.9(a) shows the positive SIMS spectrum of a silica-supported zirconium oxide catalyst precursor, freshly prepared by a condensation reaction between zirconium ethoxide and the hydroxyl groups of the support [17]. Note the simultaneous occurrence of single ions (Ff, Si, Zr and molecular ions (SiO, SiOFf, ZrO, ZrOFf, ZrtK. Also, the isotope pattern of zirconium is clearly visible. Isotopes are important in the identification of peaks, because all peak intensity ratios must agree with the natural abundance. In addition to the peaks expected from zirconia on silica mounted on an indium foil, the spectrum in figure Bl. 25.9(a)...

The reseai ch has been carried out by the liquid chromatograph Perkin-Elmer (Series 200), which has tandem detectors the diode array (X=210 nm) and the refractometer. The temperature of a column was 30 C, speed of a mobile phase is 1.5 ml/ min. As a mobile phase, mixtures of solvents methanol - water and acetonitrile - water with addition of sodium perchlorate. The columns with the modified silica gel C8 and Cl8 (4.6x220 mm, 5 pm) were used for sepai ation of the AIST and FAS components. In order to make the identification of AIST and FAS components more reliable the ratio of the values of the above-mentioned detectors signals of each substance analyzed. 

Figure 12.7 Cliromatograms of a polycarbonate sample (a) microcolumn SEC ti ace (b) capillary GC ti ace of inti oduced fractions. SEC conditions fused-silica (30 cm X 250 mm i.d.) packed with PL-GEL (50 A pore size, 5 mm particle diameter) eluent, THE at aElow rate of 2.0ml/min injection size, 200 NL UV detection at 254 nm x represents the polymer additive fraction ti ansfeired to EC system (ca. 6 p-L). GC conditions DB-1 column (15m X 0.25 mm i.d., 0.25 pm film thickness) deactivated fused-silica uncoated inlet (5 m X 0.32 mm i.d.) temperature program, 100 °C for 8 min, rising to 350 °C at a rate of 12°C/min flame ionization detection. Peak identification is as follows 1, 2,4-rert-butylphenol 2, nonylphenol isomers 3, di(4-tert-butylphenyl) carbonate 4, Tinuvin 329 5, solvent impurity 6, Ii gaphos 168 (oxidized). Reprinted with permission from Ref. (14).

The exact nature of the dead volume is complex and, in fact, will vary from solute to solute due to the exclusion properties of the stationary phase, particularly if the stationary phase or support is silica or silica based. Thus, to measure (Vo) accurately, a non-adsorbed solute of the same molecular size as the solute should be used and then the correct retention volume (V r) can be calculated and employed for identification purposes. 

The identification of bi-layer adsorption of polar solvents on the surface of silica gel arose from some work by Scott and Kucera (5) who measured the adsorption isotherms of the some polar solvents, ethyl acetate, isopropanol and tetrahydrofuran from n-heptane solutions onto silica gel. The authors found that the experimental results for the more polar solvents did not fit the simple mono-layer adsorption equation and, as a consequence, the possibility of bi-layer adsorption on the silica gel surface was examined. 

It is fruitless to attempt detailed study of a phenomenon whose products are not well identified. It is unfortunately frequently noted in the literature, especially in cases of column chromatography, that fractions are only identified as to the chemical operations which brought them to light. Fractions are identified, for example, only by the solvent used. Speculations as to the composition of the radioactive solutes in such solutions can seldom be really reliable, and the presence of an unexpected radioactive species is in such cases undetectable. It is also important in reading the literature to watch out for cases in which the chemical yields of the carriers have not been measured. Extensive decomposition can often occur on silica gel and alumina columns, especially when photosensitive or moisture sensitive compounds are used. For these reasons much of the information now existing in the literature must be regarded as only exploratory, awaiting the development of better analytical methods for separation, purification, identification and determination of the products —known or expected. 

Singh J, van Vlijmen H, Liao Y, Lee WC, Cornebise M, Harris M, Shu I, Gill A, Cuervo JH, Abraham WM, Adams SP. Identification of potent and novel a4pi antagonists using in silica screening. J Med Chem 2002 45 2988-93. 

About 15 anthocyanins in bilberries (Vaccinium myrtillus L.) were reported by Ichiyanagi et al. using CZE separation and MS-NMR identification.Anthocyanin analysis of strawberry and elderberry extracts was performed by reverse HPLC at pH 1.8 and CZE using a standard silica capillary and pH 8.0 running buffer. Under these conditions, HPLC had more advantages than CZE in terms of anthocyanin separation in these extracts." ... 

The results presented here for silicas and aluminas illustrate that there is a wealth of structural information in the infrared spectra that has not previously been recognized. In particular, it was found that adsorbed water affects the lattice vibrations of silica, and that particle-particle Interactions affect the vibrations of surface species. In the case of alumina, it was found that aluminum oxides and hydroxides could be distinguished by their infrared spectra. The absence of spectral windows for photoacoustic spectroscopy allowed more complete band identification of adsorbed surface species, making distinctions between different structures easier. The ability to perform structural analyses by infrared spectroscopy clearly indicates the utility of photoacoustic spectroscopy. 

The testing of impnrities in active pharmacentical ingredients has become an important initiative on the part of both federal and private organizations. Franolic and coworkers [113] describe the utilization of PLC (stationary phase — silica gel and mobile phase — dichloromethane-acetonitrile-acetone (4 1 1, v/v)) for the isolation and characterization of impurities in hydrochlorothiazide (diuretic drug). This drug is utilized individually or in combination with other dmgs for the treatment of hypertension. The unknown impurity band was scraped off the plate and extracted in acetonitrile. The solution was filtered and used for LC/MS and NMR analysis. The proposed procedure enabled the identification of a new, previonsly nnknown impurity. It was characterized as a 2 1 hydrochlorothiazide-formaldehyde adduct of the parent drug substance. 

Chloroform-methanol extracts of Borrelia burgdorferi were used for the identification of lipids and other related components that could help in the diagnosis of Lyme disease [58]. The provitamin D fraction of skin lipids of rats was purified by PTLC and further analyzed by UV, HPLC, GLC, and GC-MS. MS results indicated that this fraction contained a small amount of cholesterol, lathosterol, and two other unknown sterols in addition to 7-dehydrocholesterol [12]. Two fluorescent lipids extracted from bovine brain white matter were isolated by two-step PTLC using silica gel G plates [59]. PTLC has been used for the separation of sterols, free fatty acids, triacylglycerols, and sterol esters in lipids extracted from the pathogenic fungus Fusarium culmorum [60]. 

TLC is used to determine copper in aluminum alloys. The process involves the sampling of the investigated material by anodic dissolution, development of TLC plate with acetone -f HCl -f HjO (70 15 15), and the identification of analyte by 1-(2-pyridylazo)-2-naphthol [70]. A TLC system comprising silica gel as stationary... 

CUSO4, HgCli Fresh water Silica gel G 0.1-1% Identification of ionized 72... 

After the identification of the suitable compound bands, silica gel is scraped off the plates, placed in short glass columns, Pasteur pipettes, or sintered filter funnels, and fractions are recovered with such volatile solvents as ethyl acetate or dichloromethane. 

Fi re 4.15 Separation of the tricyclic antidepressant amitriptyline and its major metabolites on a 10 cm x 4.6 mm I. D. column packed with Spherisorb S5H silica with methanol-aqueous ammonium acetate (9 1), pH 9.1, as mobile phase at a flow rate of about 1 ml/min. Peak identification 1 > amitriptyline-N-oxide 2 amitriptyline 3 - E-lO-hydroxyamitriptyline 4 - Z-10-hyroxyamitriptyline 5 desmethylnortrlptyline 6 nortriptyline 7 E-lO-hydroxynortriptyline and 8 - Z-lO-hydroxynortriptyline. (Reproduced with permission from ref. 271. Copyright Elsevier Scientific Publishing Co.)... 

Figure 7.7 Separation of ethynyl estrogens on silica gel 60 HPTLC plates using two 15-min developments in the solvent system hexane-chloroform-carbon tetrachloride-ethanol (7 18 22 1 v/v). Identification O methyl green (lane marker) 1 17a-ethynylestradiol ...

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

Figure 6 Separation of basic proteins on an untreated fused silica capillary with diaminopropane as buffer additive. Capillary 75 cm (55 cm to detector) x 50 p i.d. Buffer pHs are as noted on the figure with 30 to 60 mM DAP as an additive 200 to 240 V/cm peak identification 1 = lysozyme, 2 = cytochrome, 3 = ribonuclease, 4 = a-chymotrypsin 5 = trypsinogen, 6 = r-huIL-4. (From Bullock, J. A. and Yuan, L.-C., /. Microcol. Sep., 3, 241, 1991. With permission.)...

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