Standard Silica Solutions

Several recent NMR studies have alloHed the identification of about tnenty silicate oligomers and quantitative or semi-quantitative estimates of their respective concentrations. In spite of the precautions used by some authors, the measured concentrations and in particular the experimental monomer concentration (used as a basis in our calculations) are probably not alaays very accurate expecial-ly in the case of the less alkaline or the more concentrated (in silica) solutions. The use of an inert silicon-containing internal standard could perhaps be useful. To this lack of accuracy is added the uncertainty of the pH measurement in such strongly alkaline solutions. 

Passage of salts and silica is much lower for polyamide membranes than for CA membranes. Some membranes can achieve 99.7+% rejection on a standard test solution (2,000 ppm NaCl solution at 225 psi... 

Standard Phosphate Solution Prepare a 9.0-mM phosphate stock solution. Dissolve and dilute 612.4 mg of potassium dihydrogen phosphate (KH2P04) (dried in desiccator with silica) to 500 mL with water in a volumetric flask. Make the following dilutions in water from the stock solution, and use these as standards. 

A solution containing the surfactant and a portion of the solvent is often prepared separately from the silica solution and allowed to equilibrate. The larger molecular weight triblock copolymers may take some time to dissolve and should be allowed to equilibrate in solution to standardize the preparation of the coating solution. As there are no reactions taking place in these solutions, they may be stored and kept after preparation. A typical solution consists of 1.7 g Pluronic P123 (EO20PO70EO20) and 8g of ethanol. ... 

Standard tantalum solution 1 mg/ml. Fuse 0.1220 g of Ta205, with 4 g of K2S2O7 in a silica or platinum crucible. Dissolve the melt in 4% (NH4)2C204 solution and dilute to the mark with the same reagent in a 100-ml standard flask. Working solutions are obtained by suitable dilution of the stock solution with 2% solution of ammonium oxalate. 

Standard silicon solution 0.1 mg/ml. Fuse 0.2140 g of ignited and comminuted silica, SiOa, with 2 g of Na2C03 in a platinum crucible. Dissolve the melt in water, dilute the solution with water to -900 ml, acidify with 1 M H2SO4 to pH -1.5, and make up the solution to volume in a l-litre standard flask with water. 

Standard Solution and TLC. A 0.25% (w/v) of each of the alkaloid bases in MeOH CHCl3 (1 4) is taken as standard alkaloid solution. MeOH CHCl3 (1 9) is used as developing solvent for morphine, codeine, and thebaine, and EtOH C6H6 (1 4) for papaverine and narcotine TLC on silica gel... 

TLC coupled to ESI was used for the analysis of monomeric flavanols and proan-thocyanidins from standard stock solutions and from extracts of natural samples. Specifically, standard solutions of (-)-epicatechin, (+)-catechin, procyanidin B2, (-)-epigallocatechin, and extracts of pomegranate peel and juniper seeds were developed on HPTLC cellulose plates and HPTLC silica gel 60 plates. Effects of eluent flow, sorbent material, and developing solvent on TLC-ESI mass spectra were studied. A CAMAG TLC-MS interface was used for the elution of compounds from HPTLC plates into the ESI source. For silica plates, it was necessary to use an HILIC guard column mounted between the CAMAG TLC-MS interface and ion source. This need was caused by the presence of stationary phase impurities in the... 

The reaction of silica with catechol, pyrocatechol, and 2,3-naphthalenediol has been studied by several investigators (158-162), but Bartels and Erlenmeyer appear to have been the only ones to use this reaction to characterize the rate of depolymerization of silica (163a). For example, monomeric silicic acid from ethyl silicate in a standard solution of catechol in 0.8 N HCl reacted rapidly and could be titrated to a constant pH of 8.5 with an equivalent amount of standard NaOH solution in a few minutes. An equivalent amount of silica gel required 2.5 hr, but ignited gel reacted only slightly in 5 hr. The rate of reaction, followed by a constant pH titration, provides a way to estimate the relative degree of polymerization of silica or possibly the specific surface area. 

Passage of salts and silica is much lower for polyamide membranes than for CA membranes. Some membranes can achieve 99.7+% rejection on a standard test solution (2,000 ppm NaCl solution at 225 psi (1.6 MPa), 77 F (25"C), pH = 8, and 15% recovery). The salt passage at this rejection is only 0.3%, while the salt passage for high-rejection CA membranes at 98% rejection is 2%. So, the salt passage is nearly 7-fold lower for polyamide membranes than for CA membranes. See Chapter 3, Table 3.2 for complete rejection capabilities for polyamide membranes. 

Establish the calibration graph as follows Measure appropriate amounts of standard boron solution (0 5716 g boric acid per litre, 1 ml = 100 /ig boron) into a series of 25-ml silica dishes and carry out the whole procedure as described above. The amounts should be chosen so that the 2 ml aliquots taken from the 25-ml volumes cover the range... 

Protocol 1 The reaction was performed in a CEM Discover 1-300 W system equipped with a built-in pressure measurement sensor and a vertically focused IR temperature measurement sensor using the mode Discover Standard. A solution of 5,5-dimethyl-2-diazocyclohexan-1,3-dione (1, 115 mg, 0.69 mmol), benzaldehyde (70 pL, 0.69 mmol), and fR)-phenylethylamine (88 p,L, 0.69 mmol) in 2mL of anhydrous toluene (0.35 M) under an argon atmosphere in a 10-mL sealed borosilicate tubular reaction vessel containing a Teflon-coated magnetic stirring bar was irradiated at 140 °C for 5 minutes after a ramp-up time of 2 minutes (total irradiation time = 7 minutes). The resulting reaction mixture was cooled to 50 °C by air flow, concentrated, and directly purified by flash chromatography on silica gel eluted with EtOAc/petrol ether to afford the... 

Egg shell type catalysts are used in the catalytic test measurements. Thin layers of the active compounds have been fixed on nonporous steatite pellets (2-3 mm diameter) using a colloidal silica solution (DuPont Ludox AS-40) as a binder. The tests are performed in an integral flow reactor using a standard gas mixture containing 4% O2,1000 ppm NO and 1200 ppm NHj in nitrogen. The gas stream passes over 5 g catalyst with 3 wt% of the active compound. The space velocity, calculated with respect to the total catalyst volume including the inert carrier, is maintained at 29000 h. ... 

Caffeine is extracted from beverages by a solid-phase microextraction using an uncoated fused silica fiber. The fiber is suspended in the sample for 5 min and the sample stirred to assist the mass transfer of analyte to the fiber. Immediately after removing the fiber from the sample it is transferred to the gas chromatograph s injection port where the analyte is thermally desorbed. Quantitation is accomplished by using a C3 caffeine solution as an internal standard. 

Caffeine in coffee, tea, and soda is determined by a solid-phase microextraction using an uncoated silica fiber, followed by a GC analysis using a capillary SPB-5 column with an MS detector. Standard solutions are spiked with G3 caffeine as an internal standard. 

Photomultipliers are used to measure the intensity of the scattered light. The output is compared to that of a second photocell located in the light trap which measures the intensity of the incident beam. In this way the ratio [J q is measured directly with built-in compensation for any variations in the source. When filters are used for measuring depolarization, their effect on the sensitivity of the photomultiplier and its output must also be considered. Instrument calibration can be accomplished using well-characterized polymer solutions, dispersions of colloidal silica, or opalescent glass as standards. 

Procedure. Allow the whole of the sample solution (1 L) to flow through the resin column at a rate not exceeding 5 mL min . Wash the column with 250 mL of de-ionised water and reject the washings. Elute the copper(II) ions with 30 mL of 2M nitric acid, place the eluate in a small conical flask (lOOmL, preferably silica) and evaporate carefully to dryness on a hotplate (use a low temperature setting). Dissolve the residue in 1 mL of 0.1 M nitric acid introduced by pipette and then add 9 mL of acetone. Determine copper in the resulting solution using an atomic absorption spectrophotometer which has been calibrated using the standard copper(II) solutions. 

A calibration curve for the range 0.2-10 mg fluoride ion per 100 mL is constructed as follows. Add the appropriate amount of standard sodium fluoride solution, 25 mL of 2-methoxyethanol, and 10 mg of a buffer [0.1 Af in both sodium acetate and acetic (ethanoic) acid] to a 100 mL graduated flask. Dilute to volume with distilled water and add about 0.05 g of thorium chloranilate. Shake the flask intermittently for 30 minutes (the reaction in the presence of 2-methoxyethanol is about 90 per cent complete after 30 minutes and almost complete after 1 hour) and filter about 10 mL of the solution through a dry Whatman No. 42 filter paper. Measure the absorbance of the filtrate in a 1 cm cell at 540 nm (yellow-green filter) against a blank, prepared in the same manner, using a suitable spectrophotometer. Prepare a calibration curve for the concentration range 0.0-0.2 mg fluoride ion per 100 mL in the same way, but add only 10.0 mL of 2-methoxyethanol measure the absorbance of the filtrate in a 1 cm silica cell at 330 nm. 

Standard solution of silica. Fuse 0.107 g of pure, dry precipitated silica with 1.0 g of anhydrous sodium carbonate in a platinum crucible. Cool the melt, dissolve it in de-ionised water, dilute to 500 mL, and store in a polythene bottle. 1 mL = 0.1 mg Si. Dilute as appropriate, say, to 1 mL = 0.01 mg Si. 

After extraction of the neutral oil from the AOS sample, the neutral oil is made up volumetrically to at least a 10% solution in hexane. Of this solution 4 pi is spotted onto a silica gel TLC plate, together with terminal 5-sultone standard in the range 0.4-4 pg (equivalent to 0.1-1% sultone in the neutral oil). It is twice developed in a chamber saturated with 2-propyl ether. The solvent is completely evaporated and the spots visualized by vapor phase sulfuric acid charring using the technique described by Martin and Allen [139]. Humidity is not critical (10-30% is optimum) and activation of the plates has not been found necessary, but it might be required under conditions of high humidity. The level of sultone can be estimated by visual comparison with the standards or by the use of a densitomer. 

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