Supernatant solution

Several variations of the chemical method are in use. In the one described below, a freshly prepared Fehling s solution is standardised by titrating it directly against a standard solution of pure anhydrous glucose when the end-point is reached, I. e., when the cupric salt in the Fehling s solution is completely reduced to cuprous oxide, the supernatant solution becomes completely decolorised. Some difficulty is often experienced at first in determining the end-point of the reaction, but with practice accurate results can be obtained. The titrations should be performed in daylight whenever possible, unless a Special indicator is used (see under Methylene-blue, p. 463). 

Xanthylamides. Dissolve 0 25 g. of xanthhydrol in 3-5 ml. of glacial acetic acid if an oil separates (as is sometimes the case with commercial material), allow to settle for a short time and decant the supernatant solution. Add 0-25 g. of the amide, shake and allow to stand. If a crystalline derivative does not separate in about 10 minutes, warm on a water bath for a period not exceeding 30 minutes, and allow to cool. Filter oflF the solid xanthylamide (9-acylamidoxanthen) and recrystallise it from dioxan - water or from acetic acid - water, dry at 80° for 15 minutes and determine the m.p. 

The vanadium pentoxide catalyst Is prepared as follows Suspend 5 g. of pure ammonium vanadate in 50 ml. of water and add slowly 7 5 ml. of pure concentrated hydrochloric acid. Allow the reddish-brown, semi-colloidal precipitate to settle (preferably overnight), decant the supernatant solution, and wash the precipitate several times by decantation. Finally, suspend the precipitate in 76 ml. of water and allow it to stand for 3 days. This treatment renders the precipitate granular and easy to 6lter. Filter the precipitate with suction, wash it several times with cold 5 p>er cent, sodium chloride solution to remove hydrochloric acid. Dry the product at 120° for 12 hours, grind it in a mortar to a fine powder, and heat again at 120° for 12 hours. The yield of catalyst is about 3 - 5 g. 

Conduct the preparation in the fume cupboard. Dissolve 250 g. of redistilled chloroacetic acid (Section 111,125) in 350 ml. of water contained in a 2 -5 litre round-bottomed flask. Warm the solution to about 50°, neutralise it by the cautious addition of 145 g. of anhydrous sodium carbonate in small portions cool the resulting solution to the laboratory temperature. Dissolve 150 g. of sodium cyanide powder (97-98 per cent. NaCN) in 375 ml. of water at 50-55°, cool to room temperature and add it to the sodium chloroacetate solution mix the solutions rapidly and cool in running water to prevent an appreciable rise in temperature. When all the sodium cyanide solution has been introduced, allow the temperature to rise when it reaches 95°, add 100 ml. of ice water and repeat the addition, if necessary, until the temperature no longer rises (1). Heat the solution on a water bath for an hour in order to complete the reaction. Cool the solution again to room temperature and slowly dis solve 120 g. of solid sodium hydroxide in it. Heat the solution on a water bath for 4 hours. Evolution of ammonia commences at 60-70° and becomes more vigorous as the temperature rises (2). Slowly add a solution of 300 g. of anhydrous calcium chloride in 900 ml. of water at 40° to the hot sodium malonate solution mix the solutions well after each addition. Allow the mixture to stand for 24 hours in order to convert the initial cheese-Uke precipitate of calcium malonate into a coarsely crystalline form. Decant the supernatant solution and wash the solid by decantation four times with 250 ml. portions of cold water. Filter at the pump. 

Inclusions are difficult to remove since the included material is chemically part of the crystal lattice. The only way to remove included material is through reprecipitation. After isolating the precipitate from the supernatant solution, it is dissolved... 

Occlusions are minimized by maintaining the precipitate in equilibrium with its supernatant solution for an extended time. This process is called digestion and may be carried out at room temperature or at an elevated temperature. During digestion, the dynamic nature of the solubility-precipitation equilibrium, in which the precipitate dissolves and re-forms, ensures that occluded material is eventually exposed to the supernatant solution. Since the rate of dissolution and reprecipitation are slow, the chance of forming new occlusions is minimal. 

Example of copredpitation (a) schematic of a chemically adsorbed inclusion or a physically adsorbed occlusion in a crystal lattice, where C and A represent the cation-anion pair comprising the analyte and the precipitant, and 0 is the impurity (b) schematic of an occlusion by entrapment of supernatant solution (c) surface adsorption of excess C. 

The clear supernatant solution is decanted and sold in Hquid form or concentrated to approximately 61.5 ° Bh and then allowed to soHdify to form blocks that are cmshed, ground, and graded. A typical analysis for the dry product is total A117.0—17.5% Fe202 <0.5% water of composition 42—43% insoluble <1.0%. Liquid alum contains 7.5—8.5% Al O. At concentrations >8.5% AI2O2, crystallisation of the solution may occur. 

A) Preparation of 1-(2,3,5-Tri-0-Acetyl- -D-Arat>inofuranosy/)-4-Thiouracil A mixture of 1.85 g (5.0 mmol) of 1-(2,3,5-tri-0-acetyl-(3-arabinofuranosyl)uracil, 1.23 g (5.55 mmol) of phosphorus pentasulfide, and 30 ml of pyridine was heated under gentle reflux for 2.5 hours with exclusion of moisture. The reaction mixture was cooled, and the supernatant solution was transferred by means of a pipette into a mixture of crushed ice and water. 

A solution of 600 g. of anhydrous calcium chloride in 1800 cc. of water warmed to 40° is added slowly with rapid mixing to the hot sodium malonate solution. A cheese-like precipitate of calcium malonate is formed immediately and becomes coarsely crystalline on standing for twenty-four hours. After the supernatant solution is decanted, the calcium malonate is washed by decantation four or five times with 500-cc. portions of cold water. It is then transferred to a filter, sucked as dry as possible, and dried in the air, or at 45-50°, to constant weight. The yield is 800-900 g. 

Baviere et al. [41] determined the adsorption of C18 AOS onto kaolinite by agitating tubes containing 2 g of kaolinite per 10 g of surfactant solution for 4 h in a thermostat. Solids were separated from the liquid phase by centrifugation and the supernatant liquid titrated for sulfonate. The amount of AOS adsorbed is the difference between initial solution concentration and supernatant solution concentration at equilibrium. 

The diastase activity was traditionally determined according to the Schade method in the earlier years (Schade et al., 1958). One unit of diastase activity (or more specifically, a-amylase), DN, is defined as that amoimt of enz)nne that converts 0.01 g of starch to the prescribed endpoint in 1 h at 37 °C under the experimental conditions. In this assay, a standard solution of starch, which reacts with iodine to produce a color solution, is used as a substrate for honey enzymes under the standard conditions (Rendleman, 2003). A recently developed procedure uses an insoluble, dyed starch substrate (Persano Oddo and Pulcini, 1999). As this substrate is hydrolyzed by ot-amylase, soluble dyed starch fragments are released into solution. After reaction termination and insoluble substrate removal by centrifugation, absorbance of the supernatant solution (at 620 nm) is measured. The absorbance is proportional to the diastase activity. This procedure has been widely adopted in the honey industry due to the convenience of a commercially available substrate and the simple assay format. 

An example of the second method of parenteral suspension preparation is testosterone suspension. Here, the vehicle is prepared and sterile-filtered. The testosterone is dissolved separately in acetone and sterile-filtered. The testosterone-acetone solution is aseptically added to the sterile vehicle, causing the testosterone to crystallize. The resulting suspension is then diluted with sterile vehicle, mixed, the crystals allowed to settle, and the supernatant solution siphoned off. This procedure is repeated several times until all the acetone has been removed. The suspension is then brought to volume and filled in the normal manner. 

Solubility measurement at a single pH [37-39] under equilibrium conditions is largely a labor-intensive procedure, requiring long equilibration times (12h-7 days). It s a simple procedure. The drug is added to a standard buffer solution (in a flask) until saturation occurs, indicated by undissolved excess dmg. The thermostated saturated solution is shaken as equilibration between the two phases is established. After microfiltration or centrifugation, the concentration of the substance in the supernatant solution is then determined using HPLC, usually with UV detection. If a solubility-pH profile is required, then the measurement needs to be performed in parallel in several different pH buffers. 

Treatment of the supernatant solution containing the dissolved or suspended contaminants73-76... 

Webb et al. [56] determined free penicillamine in the plasma of rheumatoid arthritis patients. Plasma ultrafiltrate was mixed with trichloroacetic acid and 4-aminobenzoic acid as internal standards, and HPLC mobile phase to determine total reduced penicillamine. Plasma was vortexed with trichloroacetic acid, the precipitated protein was removed after 15 min by centrifuging, and the supernatant solution was filtered and mixed with 4-aminobenzoic acid. In each instance, a 50-pL portion of solution was analyzed on a 25-cm column of Spherisorb-NH2 (5 pm) at 25 °C, with an electrochemical detector having dual porous graphite electrodes set at... 

Bergstrom et al. [63] used HPLC for determination of penicillamine in body fluids. Proteins were precipitated from plasma and hemolyzed blood with trichloroacetic acid and metaphosphoric acid, respectively, and, after centrifugation, the supernatant solution was injected into the HPLC system via a 20-pL loop valve. Urine samples were directly injected after dilution with 0.4 M citric acid. Two columns (5 cm x 0.41 cm and 30 cm x 0.41 cm) packed with Zipax SCX (30 pm) were used as the guard and analytical columns, respectively. The mobile phase (2.5 mL/min) was deoxygenated 0.03 M citric acid-0.01 M Na2HP04 buffer, and use was made of an electrochemical detector equipped with a three-electrode thin-layer cell. The method was selective and sensitive for mercapto-compounds. Recoveries of penicillamine averaged 101% from plasma and 107% from urine, with coefficients of variation equal to 3.68 and 4.25%, respectively. The limits of detection for penicillamine were 0.5 pm and 3 pm in plasma and in urine, respectively. This method is selective and sensitive for sulfhydryl compounds. 

The reaction is complete when the clear supernatant solution in the reaction vessel no longer contains chlorine as detected by the addition of dilute nitric acid and silver nitrate solution to ca. 1-ml. of the clear solution withdrawn from the reaction flask. After the reaction is complete, the ice bath is removed, and stirring is continued for 2 hours at room temperature. After standing overnight, the dimethylammonium chloride is filtered and washed with n-hexane, with careful exclusion of the moisture of the atmosphere. The combined filtrates are distilled at atmospheric pressure to remove the solvent. The tris(dimethylamino)arsine distills at 36°/2 mm. (55 to 57°/10 mm.). The yield is 402 g. (78%). 

Figure 1 ESI-mass spectrum of supernatant solution from dissolution of calcined silicalite-1 in NH4OH at 190°C...

Figure 2 Distribution of silicate species present in supernatant solution of silicalite-1 in NH4OFI at 190°C as a function of their size according to ESI-mass spectrometry.

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