Indirect measurement

A chromatographic peak may be characterized in many ways, two of which are shown in Figure 12.7. The retention time, is the elapsed time from the introduction of the solute to the peak maximum. The retention time also can be measured indirectly as the volume of mobile phase eluting between the solute s introduction and the appearance of the solute s peak maximum. This is known as the retention volume, Vr. Dividing the retention volume by the mobile phase s flow rate, u, gives the retention time. 

The well-known DLVO theory of coUoid stabiUty (10) attributes the state of flocculation to the balance between the van der Waals attractive forces and the repulsive electric double-layer forces at the Hquid—soHd interface. The potential at the double layer, called the zeta potential, is measured indirectly by electrophoretic mobiUty or streaming potential. The bridging flocculation by which polymer molecules are adsorbed on more than one particle results from charge effects, van der Waals forces, or hydrogen bonding (see Colloids). 

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. 

Total Solids Recovery In clarification, the clarity of the effluent is measured indirectly by the total sohds recovered in the cake as... 

Another property of importance is the pore volume. It can be measured indirectly from the adsorption and/or desorption isotherms of equilibrium quantities of gas absorbed or desorbed over a range of relative pressures. Pore volume can also be measured by mercury intrusion techniques, whereby a hydrostatic pressure is used to force mercury into the pores to generate a plot of penetration volume versus pres- sure. Since the size of the pore openings is related to the pressure, mercury intrusion techniques provide information on the pore size distribution and the total pore volume. 

Temperature is measured indirectly, by observing its effect on the properties of a substance. A mercury-in-glass thermometer takes advantage of the fact that mercury, like other substances, expands as temperature increases. When the temperature rises, the mercury in the thermometer expands up a narrow tube. The total volume of the tube is only about 2% of that of the bulb at the base. In this way, a rather small change in volume is made readily visible. 

Koopmanschap MA et al (1995) The friction cost for measuring indirect costs of disease, J Health Econ 14 171-189... 

Transfer of polarization from C nuclei to H nuclei and their subsequent detection leads to a 16-fold increase in sensitivity because the C magnetization is being measured indirectly through detecting it via the nucleus with the higher magnetogyric ratio (i.e., H). Irradiation of the protons between the scans causes a further threefold increase in the population of the C nuclei due to nOe, so an overall 50-fold increase in sensitivity is achievable in contrast to direct C measurements. However, because of... 

Composition is another variable that is often measured indirectly. A temperature-sensing device is often used at the top of an atmospheric distillation... 

The second estimate of dose was arrived at through analysis of the collected urine of volunteers for 3,5,6-TCP and creatinine. The second approach is generally considered to yield a more accurate estimate of dose as it measures, indirectly, the amount of test substance absorbed from all routes of exposure. The following estimation of dose is for the liquid turf evaluation only a summarization of data will be given for the granular turf evaluation. 

The viscosity coefficients at dislocation cores can be measured either from direct observations of dislocation motion, or from ultrasonic measurements of internal friction. Some directly measured viscosities for pure metals are given in Table 4.1. Viscosities can also be measured indirectly from internal friction studies. There is consistency between the two types of measurement, and they are all quite small, being 1-10% of the viscosities of liquid metals at their melting points. It may be concluded that hardnesses (flow stresses) of pure... 

The estimated value of k30 is about two orders of magnitude larger than the value obtained by extrapolation to room temperature of Schott and Davidson s rate expression278 (Table 19). The above k 45/k46 value for M = Kr appears to be grossly inconsistent3 06 with the value of Johnston et al.299 for M = N2 (Table 21) approximately extrapolated to room temperature or with the ratio calculated from Burnett s expression304 for k-4S and Husain and Norrish s estimate250 for k46 (Table 21). Berces et al,307 measured indirectly k46 and obtained a value 7 times smaller than the value of Husain and Norrish in Table 21. All these inconsistencies point out the need for further work with these kinetically very complex systems. 

Exposure. Exposure to 1,3-DNB is currently measured indirectly by determining levels of methemoglobin in the blood (Donovan 1990). However, increased methemoglobin formation is not a specific response to 1,3-DNB exposure and may occur after exposure to other nitrobenzene compounds such as the other two isomers of dinitrobenzene. Determination of methemoglobin levels is widely used and is a reliable detection method. Very few methods are available for direct evaluation of 1,3-DNB levels, and they are not extensively used, probably because of the relatively rapid rate of conversion of 1,3-DNB to its degradation products (Cossum and Rickert 1985). Preliminary data suggested that the formation of adducts of 1,3,5-TNB with tissue DNA and/or with blood proteins may be useful as markers for exposure to 1,3,5-TNB (Reddy et al. 1991). Further research with both 1,3-DNB and 1,3,5-TNB in the area of adduct formation could provide valuable additional information. 

Vicat Kate of absorption of calcium measured indirectly front a saturated CatOHb solution in contact with excess C atOH), (solid) by determining residual Ca(OI I),. Residual free portlandite is measured by DTA. TG. or solvent extraction. Correlation with strength gain is poor... 

Ai and Suzuki [5,9] investigated the combination V2Os—P2Os. The acidity was measured indirectly by the activity for dehydration of isopropanol and was shown to decrease with increasing P2Os content. The activity for the oxidation of butene-1 and butadiene to maleic acid anhydride decreased accordingly. It was shown that the adsorption equilibrium constant of the olefin on the catalyst also decreased in the same way. 

This spectrophotometric method is for determining ozone at low liquid concentrations (0.02-2.5 mg L l 03). The direct oxidation ofN,N-diethyl-l,4 phenylenediammonium (DPD) by ozone is very slow. Therefore, the concentration of ozone is measured indirectly by the oxidation of iodide with ozone (pH = 6). 

This difference in kinetics was exploited to develop a procedure to determine free and reversibly bound sulfite in food. The mobile phase consisted of an aqueous solution of 0.05 M tetra-butylammonium hydroxide adjusted to the desired pH by the addition of glacial acetic acid (34). Fluorimetric detection is also possible, because a reaction of the formaldehyde-bisulfite complex with 5-aminofluorescein gives a nonfluorescent product. The sulfite is measured indirectly by its suppresion of the fluorescence of the reagent (31). This method is applicable to the determination of S02 at > 10 ppm and is not applicable to dark-colored foods or ingredients where SO, is strongly bound, e.g., caramel color. This method does not detect naturally occurring sulfite. Sulfur dioxide is released by direct alkali extraction. 

Pressure drop H2O (liquid) Simple technique, real-time measurements Indirect measurement, pressure drop not solely... 

The impedance hygrometer measures the water content of a sample by means of a probe whose electrical impedance is a function of the vapor pressure of moisture in the fluid. The probe consists of an aluminum strip that is anodized to form a porous layer of aluminum oxide. A thin coat of gold is applied over the aluminum oxide. Water vapor penetrates the gold layer and equilibrates on the aluminum oxide. Leads from the gold and aluminum electrodes of the probes connect the sensing element to the measuring circuitry. The moisture content of solids can also be measured indirectly by detecting the moisture in the atmosphere above or near the process solids because the atmosphere near the solids is in equilibrium with the moisture content of the process materials. 

Figure 6. Time course of change in catalytic specificity (upper panel) and Ca2+ dissociation from extracytoplasmic low affinity sites (lower panel) following phosphorylation of the SR Ca2+-ATPase with ATP. The amount of ADP-insensitive phosphoen-zyme (E2P) was measured in two ways (I) [y-32P]ATP was included in the reaction mixture and the radioactivity incorporated into the enzyme was determined after acid quenching at various time intervals. To remove the ADP-sensitive phosphoenzyme so that only ADP-insensitive phosphoenzyme was measured, ADP was added 4 sec before the quench (upper panel, right scale) (2) by the enhancement of fluorescence from a trinitrophenyl-derivative of ADP bound in the catalytic site in exchange with ADP after the phosphorylation (upper panel, left scale). The change in Ca2+ binding was measured indirectly by use of murexide as an indicator of free Ca2+ in the medium. The data show that Ca2+ dissociates simultaneously with formation of E2P. The data points were taken from Andersen et al., 1985.

---