Gravimetric determinations, analytical

Gemand, W., Steckenreuter, K., and Wieland, G., Greater Analytical Accuracy through Gravimetric Determination of Quantity, Fresenius Z. Anal. Chem. 334, 1989, 534-539. 

TABLE 11.20 Elements Precipitated by General Analytical Reagents This table includes the more common reagents used in gravimetric determinations. The lists of elements precipitated are not in all cases exhaustive. The usual solvent for a precipitating agent is indicated in parentheses after its name or formula. When the symbol of an element or radical is italicized, die element may be quantitatively determined by the use of the reagent in question. ... 

Our review on the use of oximes and hydroxamic acids in inorganic analytical chemistry showed that these reagents are/were most frequently used for gravimetric determinations, determinations based on complexation, spectrophotometric determinations and separations, while their use for column separations, as electrode sensors, as supporting electrolytes or compounds that enhance sensitivity of determination is less common. Additionally, it was noticed that the analytical chemistry of anions is less advanced than that of cations and for this reason this chapter was limited to analytical chemistry of metallic cations. 

Comprehensive accounts of the various gravimetric, polarographic, spectrophotometric, and neutron activation analytical methods have been published (1,2,5,17,19,65—67). Sampling and analysis of biological materials and oiganic compounds is treated in References 60 and 68. Many analytical methods depend on the conversion of selenium in the sample to selenous acid, H SeO and reduction to elemental selenium when a gravimetric determination is desired. 

Firstly, when relating (gravimetrically determined) equilibrium film composition to solution composition, activity effects must be taken into account. These effects may cause solvent and other neutral molecules, as well as the target species, to enter/leave the film. The importance of medium effects cannot be overemphasised here. A special case is a co-ordination model, where favourable interaction between polymer and target species results in saturation of the film except at very low concentration. The film mass is then independent of solution composition. This situation is likely for systems where a strong, specific polymer/analyte interaction has been synthetically designed into the polymer. 

The possibility of using Raman spectroscopy to monitor BTUs was suggested in 1980 (17). A set of 10 samples containing methane and isobutane in nitrogen were prepared and used to determine the feasibility of using Raman spectra to predict concentrations of the three analytes. The differences between spectrometrically and gravimetrically determined concentrations did... 

Analytical gravimetric determination beakers, crucible and cover, funnel, desiccator, drying oven, Meker burner, analytical balance, support stand and crucible support triangle... 

Using modem electronics and/or well-designed potentiostats, both controlled-potential coulometry and controlled-current coulometry can be performed, as can gravimetric determinations of analytes. Figure 11.68 shows a potentiostat that uses three operational amplifiers. 

Thiopyrylium salts can find application in analytical chemistry. Thus, 2,4,6-triphenylthiopyrylium chloride can be used as a precipitant for the quantitative gravimetric determination of anions (CIO4", 103 , NOj , BF4 ) (87MI3). Thiopyrylium salts can be also used in the spectrophoto-metric determination of bismuth (75URP482648), tellurium (77URP-558856), palladium (77URP558865), and alkyl sulfates (91URP1675746). 

JJ Gravimetric Determination of Sulphate in Comprehensive Analytical Chemistry. C. Willson, and D. Willson, Eds., Vol. 1C. Elsevier Publishing Company. Amsterdam, Netherlands. 1962. p. 282. 

Measurement of moisture uptake is typically done by either of two general methods. The classical approach involves equilibration of solid at several different humidities and the subsequent determination of water content either by gravimetric or analytical methods such as Karl Fischer titration or loss on drying. Moisture adsorption or desorption may be measured by use of this method and the pro-... 

Modern analytical instrumentation has been used in the last 23 years for determining commercially important characteristics of soluble silicates, and the nature of silicate species in silicate glasses and solutions. The classical wet methods for assay of silicate solutions are alkali titration and gravimetric determination of silica, which can also be determined, with lesser precision, by the alkali fluosilicate method. 

For many years, analytical chemistry relied on chemical reactions to identify and determine the components present in a sample. These types of classical methods, often called wet chanical methods, usually required that a part of the sample be taken and dissolved in a suitable solvent if necessary and the desired reaction carried out. The most important analytical fields based on this approach were volumetric and gravimetric analyses. Acid-base titrations, oxidation-reduction titrations, and gravimetric determinations, such as the determination of silver by precipitation as silver chloride, are all examples of wet chemical analyses. These types of analyses require a high degree of skill and attention to detail on the part of the analyst if accurate and precise results are to be obtained. They are also time consuming, and the demands of today s high-throughput pharmaceutical development labs, forensic labs, commercial environmental labs, and industrial quality control... 

Analytical techniques have been developed from simple chemical/gravimetric determinations. 

Wet analytical methods may be used to verify the composition and, to a lesser degree, the purity of the trichlorides. We ed samples should generally be dissolved in water in a closed container to avoid loss of HG through hydrolysis. Titrimetric methods for the rare earth elements together with gravimetric determination of chloride will typically give analytical compositions of C1 M = 3.00 0.01 with 100 0.2% weight recovery as metal plus chloride. 

The importance of the analytical control depends on the preparation tolerance of the mixture method applied. In case of preparation methods with higher inaccuracies it is common practice to determine the mole fraction by means of analysis. Even if the mixture is gravimetrically produced, analytical control cannot be renounced. On the one hand, it can never be excluded, for instance, that systematic weighing errors or individual errors of the operator occur. On the other hand, above all in case of corrosive components, adsorption effects and reactions with the inner surface of the gas cylinder cannot be excluded. Such effects can only be detected analytically. 

The methods used for determination of fat or oil in food are often based on extraction with either ethyl ether or petroleum ether and gravimetric determination of the extraction residue. These methods may provide unreliable or incorrect results, particularly with food of animal origin. As shown in Table 14.20, where a corned beef sample was analyzed, the amount and composition of fatty acids in the fat residue were influenced greatly by the analytical methods used. In addition to the accessible free lipids, the emulsifiers present and the changes induced by autoxidation affect the amount of extractable lipids and the lipid-to-nonlipid ratio in the residue. The use of a standard method still does not eliminate the disadvantages shown by analytical methods of fat analysis. Therefore, in questionable cases, quantitative determination of fatty acids and/or glycerol is recommended. 

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