Double precipitation

Determination of tungsten as the trioxide (tannic acid-phenazone method) Discussion. Tungstic acid is incompletely precipitated from solutions of tungstates by tannic acid. If, however, phenazone (2,3-dimethyl-l-phenyl-5-pyrazolone) is added to the cold solution after treatment with excess of tannic acid, precipitation is quantitative. This process effects a separation from aluminium, and also from iron, chromium, manganese, zinc, cobalt, and nickel if a double precipitation is used. 

In view of the selective character of many colorimetric reactions, it is important to control the operational procedure so that the colour is specific for the component being determined. This may be achieved by isolating the substance by the ordinary methods of inorganic analysis double precipitation is frequently necessary to avoid errors due to occlusion and co-precipitation. Such methods of chemical separation may be tedious and lengthy and if minute quantities are under consideration, appreciable loss may occur owing to solubility, supersaturation, and peptisation effects. Use may be made of any of the following processes in order to render colour reactions specific and/or to separate the individual substances. 

A separate polymerization was carried out under identical conditions but, for this experiment, the polybutadiene fraction was separated by the double precipitation described in the Experimental section. As expected, the apparent degree of grafting was in general 50% lower than that... 

The graft polybutadiene containing both styrene and acrylonitrile prepared in a separate experiment was isolated by a double precipitation. The experimental value for the degree of grafting was calculated on the basis of the trans isomer of polybutadiene (Figure 17). Except for two fractions, the styrene contents are within the shaded band. We note that both the styrene and the acrylonitrile contents increase slightly. This phenomenon might be caused by the polymerization temperature which was lower than in the previous two experiments (100°C. instead of 110°C.). 

Despite this low degree of grafting, yc s increase with the increase in percent conversion (Figure 18). The shaded band shows the magnitude. However, the rate of increase in yc is not in proportion to the rate of increase in the degree of grafting. The double precipitation could be... 

In general, the use of a specific or selective reagent as precipitant for the element is advisable as1 is the use of a masking reagent for interfering elements. In this way a single or double precipitation procedure often becomes sufficient. 

Table 4.4 gives a list of polymers and solvents suitable for dissolving some plastics. In some cases the metal is double precipitated into aqueous medium by dropping the organic solution containing the dissolved plastic in to a rapid stirring aqueous medium of ammonia for Pb, Ag, Sn and aqueous HC1 for Cu, Fe, Cr, Ni, Sb, etc. where the metals are transferred quantitatively to the basic or acidic medium. 

Double precipitation Synonymous with reprecipitation. Drierite Trade name for calcium sulfate, a diydng agent. Dropping mercury electrode An electrode in which mercury is forced through a capillary, producing regular drops. 

Several procedures were proposed. Especially, in the case of higher silica concentrations, a double precipitation is recommended. Typically 0.08 kg Al2(S04)- I8H2O and 0.03 kg MgS04 7H2O per kg WO3 are added to the 70-80 °C hot solution after digestion. The pH value should be between 9.0 and 9.5. Filtration can be started after 1 hour. 

Sodium is separated from other alkali metals by precipitation from acetic acid medium as the triple acetate, NaZn(U02)3(CH3C00)9-9H20 [59]. When the potassium content exceeds the sodium content by greater than one hundred-fold, it is partly co-precipitated with the sodium. In this case, double precipitation is advisable. The precipitated triple acetate is then... 

From mixtures of platinum metals, Ru and Os can be separated by distillation as volatile tetroxides, and a double precipitation of Pd, Rh, and Ir hydroxides (with Fe used as collector) at pH 8 enables them to be separated from platinum. 

Strontium impurities have been isolated from calcium salts by precipitating calcium as Ca(OH)2 with NaOH solution. After double precipitation of Ca(OH)2, the amount of strontium co-precipitated had decreased to 3 ppm [36]. 

Traces of Th can be precipitated as thorium hydroxide by ammonia (pH > 4), with Fe(III), A1 or La being suitable collectors [1-2]. Thorium is separated from rare-earth elements by double precipitation (at pH 5) of the hydroxide. 

Precipitation of titanium as the hydroxide Ti(OH)4 with an excess of NaOH solution enables the separation of Ti from V(V), Cr(VI), Mo(VI), W(VI), P(V), and A1 [1,2]. Double precipitation gives the best separation. Traces of Ti are separated in the presence of Fe, Al, Mn, Mg, or La as collector. Precipitation of Ti with ammonia in the presence of EDTA separates this metal from Fe, Mn, Al, and other metals. 

When sodium carbonate is present in excess, the uranyl ion forms a soluble carbonate complex, whereas most metals separate as carbonates, basic carbonates, or hydroxides [62] — with the exception of V, Be, and Th, which remain partly in solution together with uranium. If the precipitate contains several metals, double precipitation is necessary. The amount of uranium retained by the precipitate does not exceed a few percent. When a carbonate fusion is used for decomposition of the sample, and the melt is leached with water, uranium passes into solution. 

The study of hydrogenation of hydrocarbons with pure chromia obtained by double precipitation revealed that olefins can be easily hydrogenated in the presence of this catalyst with excellent yields (Table I). 

Beryllium is separated from aluminum and iron by the complete solubility of its hydroxide in a hot saturated solution of acid sodium carbonate—ferric hydroxide and aluminum hydroxide being completely insoluble. Double precipitation i.s essential. Beryllium hydroxide must lx washed with water containing an electrolyte in solution, for when i irc it rapidly washes through the filter in a colloidal condition. 

In this kind of work, monospecificity was operationally defined by the experimental demonstration that only one molecule of the antibody population can bind to one molecule of the antigen. Under these conditions, the complex formed is soluble and a radioimmunoassay or a double precipitation must be performed to quantitate the determination. 

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