Concentration Measures

Another method which should be cited apart from the others is to pyrolyze the sample in a hydrogen atmosphere. The sulfur is converted to H2S which darkens lead-acetate-impregnated paper. The speed of darkening, measured by an optical device, provides the concentration measurement. This method attains sensitivity thresholds of 0.02 ppm. 

The main sources of error which define the accuracy are counting statistics in tracer concentration measurements, the dispersion of the tracer cloud in the flare gas stream, and the stationarity of the flow during measurements. 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

Alcohol. The number of driving under the influence of alcohol (DUl) cases reflects the enormity of the dmnken driving problem in the United States (9). Tests to measure blood alcohol concentration are conducted on blood, urine, or breath (10). In the case of urine and breath, the alcohol concentration measured is reported in terms of the equivalent blood alcohol concentration. Most states in the United States presume that a person is under the influence of alcohol with respect to driving a motor vehicle at a blood alcohol concentration of 0.10%, ie, an ethanol concentration >10 g/100 mL of blood. Some states maintain a lower necessary concentration of 0.08%. In some European countries levels are as low as 0.05%. A blood alcohol concentration of 0.10% in a 68-kg (150-lb) person is the equivalent of about four drinks of 80 proof alcohoHc beverage or four 340-g (12-oz) beers in the body at the time of the test (see Beer Beverage spirits, distilled Wine). Ethanol is metabolized at the equivalent rate of about one drink per hour. 

A particular concentration measure of acidity of aqueous solutions is pH which usually is regarded as the common logarithm of the reciprocal of the hydrogen-ion concentration (see Hydrogen-ION activity). More precisely, the potential difference of the hydrogen electrode in normal acid and in normal alkah solution (—0.828 V at 25°C) is divided into 14 equal parts or pH units each pH unit is 0.0591 V. Operationally, pH is defined by pH = pH(soln) + E/K, where E is the emf of the cell ... 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Minimum Inhibitory Concentration measured by dilution of test compound in agar inoculated with microorganism. 

The upper hmit of a gas concentration measurement range is usually 1.5 to 2.5 times the applicable emission limit. If no span value is provided, a span value equivalent to 1.5 to 2.5 times the expected concentration is used. For convenience, the span value should correspond to 100 percent of the recorder scale. 

To find the best a priori conditions of analysis, the equilibrium analysis, based on material balances and all physicochemical knowledge involved with an electrolytic system, has been done with use of iterative computer programs. The effects resulting from (a) a buffer chosen, (b) its concentration and (c) complexing properties, (d) pH value established were considered in simulated and experimental titrations. Further effects tested were tolerances in (e) volumes of titrants added in aliquots, (f) pre-assumed pH values on precision and accuracy of concentration measured from intersection of two segments obtained in such titrations. 

Fig. 15-4. Ethylene concentrations measured by the DIAL system along a 5-km path length near Menlo Park, California. The open circles are ethylene concentrations of samples taken at three ground-level locations near the line of sight and analyzed by gas chromatography. Source Murray, E. A., and Van der Laan, ). E., Appl. Opt. 17, 814-817 (1978).

Fig. 19-11. Example of tracer concentration measurements along a sampling arc.

Fig. 19-13. Three-parameter averaging-time model fitted through the arithmetic mean and the second highest 3-hr and 24-hr SOj concentrations measured in 1972 a few miles from a coal-burning power plant. Source From Larsen (21).

Three common uses of RBS analysis exist quantitative depth profiling, areal concentration measurements (atoms/cm ), and crystal quality and impurity lattice site analysis. Its primary application is quantitative depth profiling of semiconductor thin films and multilayered structures. It is also used to measure contaminants and to study crystal structures, also primarily in semiconductor materials. Other applications include depth profilii of polymers, high-T superconductors, optical coatings, and catalyst particles. ... 

BS EN 45544 Electrical apparatus used for the detection and direct concentration measurement to toxic gases. General requirements and test methods Various... 

Higher values can be used if standard is based on nuisance or odour and there are no known effects of the maximum exposure concentration measured. 

Concentration gradient Difference in concentration measured between two... 

Higson, R. L., R. F. Griffiths, C. D. Jones, and D. J. Hall. 1994. Concentration measurements around an isolated building A comparison between wind tunnel and field data. Atmospheric Environment, vol. 28, no. 11, pp. 1827-1836. 

In-use tests deal with the concentration measurements in the worker s breathing zone for various hood applications. The performance tests presented here are typically in-use tests, where normal work procedures are ongoing. 

The contaminant concentration measurement in the general ventilation exhaust will provide the best average value for room air concentration (CJ. 

The sensor is the element of an instrument directly influenced by the measured quantity. In temperature measurement the thermal mass (capacity) of the sensor usually determines the meter s dynamics. The same applies to thermal anemometers. In IR analyzers used for concentration measurement, the volume of the flow cell and the sample flow rate are the critical factors. Some instruments, like sound-level meters, respond very fast, and follow the pressure changes up to several kHz. 

Griivimat SHC 502 Gravimetric Du.st Concentration Measuring System. Operating instructions. SICK ACi Waldkirch, Germany Erwin Sick Optic Electronic Lrd. 

In spite of careful analysis of the products with the various sophisticated probes, differences in the composition are reported. All measurements indicate a zinc-deficient zinc ferrite, but the indicated zinc concentration varies from 0.2 to 0.9. The EDS measurements are based on direct zinc concentration measurements. Determinations based on magnetization and Mdssbauer spectra are obtained on zinc ferrite synthesized in more conventional processes. 

I lere, too, computer based predictions about the nature of these flames require information about the chemicals and science of diffusion flames for the predictions to be accurate. The predictions are made accurate by comparison with measured chemical species concentrations, measured temperatures, and flow characteristics. 

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