Gravimetric methods periodate

The gravimetric method depends on the sampling of flowing, particulate-laden gas from different positions across the exhaust gas duct and the determination of the mass of the particulate material. The sample is collected over a certain time period from each point. The volumetric gas flow is measured. The result is obtained by the following steps ... 

Varhelyi Kekedy studied the thermal decomposition of iodates periodates by thermo-gravimetric methods (Ref 2). They found that there is no similarity in the decomposition of univalent iodates, but most divalent iodates -decompose similarly since their decomp temps are similar. The thermal stability (ie their resistance to decomposition into iodates) increases as follows of the alkali periodates Lithermal stability of alkaline earth periodates increases in the order Ca[Pg.381]

The solubility of gases in solids imposes a serious limitation on the thermo-gravimetric method, as discussed by Guiochon (50). It is difficult to eliminate or even measure and is generally unknown. This was shown by the heating of solid ammonium nitrate initially containing I % nitric acid at 200°C for 3 h. At the end of this period, the sample contained 0.6% nitric acid. This acid has no catalytic effect on the decomposition of the sample, which gives no nitric acid under these conditions, so that only the slowness of its evaporation... 

Many practitioners also calculate average concentration based on the gravimetric method during a test. The gravimetric method measures the weight change after a test period. The evaporation rate (R va) of the chemical is calculated as follows ... 

The permeation rate is determined by the gravimetric method. The permeation device, after it has been assembled, is weighed and then placed in a temperature-controlled cavity with constant flow of nitrogen or clean air to sweep away the permeated chemical vapor. After a period of time, perhaps days, the tubing is weighed again and the permeation rate is determined by weight loss over elapsed time. Since... 

Hg(II) can be precipitated from solution in nitric acid by periodates. The precipitated HgsC 10 )2 is the basis of a gravimetric method. It can also be used for iodometric... 

Unique methods based on new principles have been developed within the past 10 years. Threonine (27,28,249) is oxidized by lead tetraacetate or periodic acid to acetaldehyde, which is determined by photometric analysis of its p-hydroxydiphenyl complex or iodometric titration of its combined bisulfite. Serine is oxidized similarly to formaldehyde, which is determined gravimetrically (207) as its dimedon (5,5-dimethyldihydro-resorcinol) derivative or photometric analysis (31) of the complex formed with Eegriwe s reagent (l,8-dihydroxynaphthalene-3,5-disulfonic acid). It appears that the data obtained for threonine and serine in various proteins by these oxidation procedures are reasonably accurate. [Block and Bolling (26) have given data on the threonine and serine content of various proteins. ]... 

In order to characterize the concentration of dust flowing inside a duct, a measured amount of dust must be extracted over a known period of time. This collection velocity must be the same as the internal duct flow velocity to avoid altering the distribution of dust particle sizes. In addition, a number of sample points over the entire duct cross sectional area is necessary to define the overall dust concentration. This method of sampling, known as gravimetric sampling under isokinetic conditions, was used to determine the dust concentrations at the various manufacturing areas in the Army Ammunition Plants. 

This is a period in which technical development was rapid. Rotary drilling led to much deeper drilling compared with the now outdated cable tool drilling. Surface mapping was insufficient to reveal the traps at greater depth, and a search was made for other methods. In 1915, the first field use was made of the torsion balance in gravimetric surveys in Czechoslo-... 

In this method, the vessel is filled with a solute, and a supercritical fluid continuously flows through the vessel. Mild flow rate is used so that the outlet stream is assumed to reach equilibrium, which is then analyzed for the solute concentration by chromatographic, spectroscopic, gravimetric, dielectric, and other techniques. The apparatus used by Bristow et al. (2001) is shown in Figure 9. Here, solute is filled in the sample vessel. Continuous flows of supercritical fluid or a fluid mixture with cosolvent are maintained. For on-line analysis, such as using UV detector, the fluid mixture is bypassed directly to the analyzer for baseline correction, and then the fluid is allowed to pass through the sample vessel. For off-line analysis, the sample is collected in the solvent or cold trap for a given period of time (f), and then analyzed for solute amount. Solubility is calculated as... 

Periodic samples are taken for analysis to ensure stability and the attainment of equilibrium. Caution must be taken to prevent leakage. After equilibration, the sample is allowed to stand for settling of the excess solids. The solution is carefully withdrawn, filtered, and diluted accordingly. The solution may be analyzed gravimetrically or with suitable analytical methods such as UV or HPLC. 

S ampling of Particulates. Ambient air suspended particulate concentration was traditionally measured gravimetrically over a 24-h period with a "Hi-Vol" sampler. However, in 1987 the EPA changed ambient particulate control to the PM10 reference method (24). In the PM method, a... 

In the past, sedimentation of a sample required an analysis over several days, whereby individual fractions were taken out after defined periods of time and evaluated by gravimetric determination, as is the case with the ANDREASEN method. Nowadays analysis equipment is employed in ceramic laboratories for sedimentation, which provides relatively fast results (Fig. 4). 

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