Indirect Concentration Determination

Descriptions of sulfuric acid analytical procedures not specified by ASTM are available (32,152). Federal specifications also describe the requited method of analysis. Concentrations of 78 wt % and 93 wt % H2SO4 are commonly measured indirectly by determining specific gravity. Higher acid concentrations are normally determined by titration with a base, or by sonic velocity or other physical property for plant control. Sonic velocity has been found to be quite accurate for strength analysis of both filming and nonfuming acid. 

Indirect EDTA determination of cesium. Cesium ion does not form a strong EDTA complex, but it can be analyzed by adding a known excess of NaBiI4 in cold concentrated acetic acid containing excess Nal. Solid Cs3Bi2I9 is precipitated, filtered, and removed. 

Avery large part of Chemistry is concerned, either directly or indirectly, with determining the concentrations of ions in solution. Any method that can accomplish such measurements... 

E693 Woody, R.C., Turley, C.P. and Brewster, M.A. (1990). The use of serum electrolyte concentrations determined by automated analyzers to indirectly quantitate serum bromide concentration. Ther. Drug Monit. 12, 490-492. 

Since the equilibrium concentrations of the reagents are determined independently from each other, additional errors bound up with the use of the indirect concentrations of the reagents do not arise. The results of the treatment of the obtained potentiometric data are presented in Tables 3.6.3 and 3.6.4. To show the advantages of the proposed method as compared with the standard titration routine, the values of p MeO obtained according to the conventional method are collected in the same tables, the values calculated using the proposed method being denoted by an asterisk. 

In AAS, FIA has been applied to hydride generation and cold vapour techniques, microsampling for flame atomic absorption, analysis of concentrated solutions, addition of buffers and matrix modifiers, dilution by mixing or dispersion, calibration methods, online separation of the matrix and analyte enrichment, and indirect AAS determinations. 

A similar problem of determining as a flmction of ionic strength for the small/large sphere configuration was experimentally studied by Vincent et al. [151] by using the indirect, concentration-depletion method. 

If auxiliary chemical reactions are involved in concentration determinations using ion-selective electrodes (end point titration, standard addition or subtraction, indirect procedures), extreme caution is required with variable sample temperatures. This is because in addition to the electrochemical effects discussed, purely chemical phenomena may become problematic (temperature dependence of equilibrium constants, solubility products, complex formation constants and activity coefficients). With the low sample flow rates commonly encountered (a few ml/minute), thermostating the solution and sample cell with the help of a quickly responding proportional controller (Orion, Series 1,000) presents no problem. 

Concentration determinations with a single standard addition (addition or subtraction techniques, as well as indirect analyses) 1 to 10% 4 to 20%... 

If the titration reaction is too slow, a suitable indicator is not available, or there is no useful direct titration reaction, then an indirect analysis may be possible. Suppose you wish to determine the concentration of formaldehyde, 1T2CO, in an aqueous solution. The oxidation of 1T2CO by... 

The concentration of fluoride in drinking water may be determined indirectly by its ability to form a complex with zirconium. In the presence of the dye SPADNS, solutions of zirconium form a reddish colored compound, called a lake, that absorbs at 570 nm. When fluoride is added, the formation of the stable ZrFe complex causes a portion of the lake to dissociate, decreasing the absorbance. A plot of absorbance versus the concentration of fluoride, therefore, has a negative slope. 

Of the six parameters shown in Figure 13.18, the most important are peak height and return time. The peak height is related, directly or indirectly, to the analyte s concentration and is used for quantitative work. The sensitivity of the method, therefore, is also determined by the peak height. The return time determines the frequency with which samples maybe injected. Figure 13.19 shows that when a second sample is injected at a time T after injecting the first sample. 

Zirconium is often deterniined gravimetrically. The most common procedure utilizes mandelic acid (81) which is fairly specific for zirconium plus hafnium. Other precipitants, including nine inorganic and 42 organic reagents, are Hsted in Reference 82. Volumetric procedures for zirconium, which also include hafnium as zirconium, are limited to either EDTA titrations (83) or indirect procedures (84). X-ray fluorescence spectroscopy gives quantitative results for zirconium, without including hafnium, for concentrations from 0.1 to 50% (85). Atomic absorption determines zirconium in aluminum in the presence of hafnium at concentrations of 0.1—3% (86). 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

The principal method used for measuring NO2 is also based on chemiluminescence (Fig. 14-3) (5). NO2 concentrations are determined indirectly from the difference between the NO and NO (NO -I- NO2) concentrations in the atmosphere. These concentrations are determined by measuring the tight emitted from the chemiluminescent reaction of NO with 03 (similar to the reaction of O3 with ethylene noted for the measurement of O3), except that O3 is supplied at a high constant concentration, and the light output is proportional to the concentration of NO present in the ambient air stream. 

Therefore some indirect methods have been worked out to determine the value of ff=0.154,259 In particular (1) salting out of organic compounds from a surface-inactive electrolyte solution, (2) F"" for 1-pentanol or other organic compounds with a high attractive interaction constant a, and (3) dependence of the capacitance minimum on thiourea concentration. It should be noted that indirect estimates based on TU adsorption give... 

Since the binding of extraneous ions considerably alters the value of lEP of an aminoacid or protein, this point is not a constant. The term isoionic point (IP) is used to designate the pH value of a pure protein in salt-free water. The direct determination of this constant is difficult and because many proteins are insoluble in the absence of salts. The isoionic point is usually determined indirectly, that is, by measuring the lEP at different concentrations of the neutral salts and extrapolating to zero concentration The value of the isoionic point may differ from lEP by more than a pH unit (Haurowitz 1963). 

These simulation data should be proved by experiment. However, it is still unknown that what microorganisms are PAOs or GAOs. Therefore the precision of model for EBPR process should be determined with indirect methods. Then with the concentration decrease of PAOs, the GAOs concentration was increased rapidly. However, this simulation result shoidd be supported by the experimental data with the identification of PAOs and GAOs. 

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