Concentration, direct measurement

In this simple case, the measured concentration directly measures the generation rate, provided the flow rate is either precisely held constant, or is also measured with high time resolution and accuracy. 

Paul J B, Collier C P, Saykally R J, Scherer J J and O Keefe A 1997 Direct measurement of water cluster concentrations by infrared cavity ringdown laser absorption spectroscopy J. Phys. Chem. A 101 5211-14... 

A similar circumstance is detectable for nitrations in organic solvents, and has been established for sulpholan, nitromethane, 7-5 % aqueous sulpholan, and 15 % aqueous nitromethane. Nitrations in the two organic solvents are, in some instances, zeroth order in the concentration of the aromatic compound (table 3.2). In these circumstances comparisons with benzene can only be made by the competitive method. In the aqueous organic solvents the reactions are first order in the concentration of the aromatic ( 3.2.3) and comparisons could be made either competitively or by directly measuring the second-order rate constants. Data are given in table 3.6, and compared there with data for nitration in perchloric and sulphuric acids (see table 2.6). Nitration at the encounter rate has been demonstrated in carbon tetrachloride, but less fully explored. ... 

Radiochemical methods of analysis take advantage of the decay of radioactive isotopes. A direct measurement of the rate at which a radioactive isotope decays may be used to determine its concentration in a sample. For analytes that are not naturally radioactive, neutron activation often can be used to induce radioactivity. Isotope dilution, in which a radioactively labeled form of an analyte is spiked into the sample, can be used as an internal standard for quantitative work. 

We saw in Section 9.3.8 that spectroscopy, in the form of LIDAR, is a very important tool for measuring ozone concentration directly in the atmosphere. A useful indirect method involves the measurement of the concentration of oxygen which is formed from ozone by photolysis ... 

Fat Content of Milk. Raw milk as well as many dairy products are routinely analyzed for their fat content. The Babcock test, or one of its modifications, has been a standard direct measure for many years and is being replaced by indirect means, particularly for production operations. The Babcock test employs a bottle with an extended and caHbrated neck, milk plus sulfuric acid [7664-93-9] to digest the protein, and a centrifuge to concentrate the fat into the caHbrated neck. The percentage of fat in the milk is read direcflv from the neck of the bottle with a divider or caHper, rea ding to... 

In principle, the two-angle interval method can produce all CBC parameters within a single measurement channel, uniquely providing ceU-by-ceU hemoglobin concentration. The mean of the concentrations provides an alternative (and direct) measurement of MCHC. The method also provides an alternative HGB measurement, because HGB may be set equal to (RBC x MCV x MCHC)/1000. This method, like the basic light-scattering method, uses the same flow cell to measure platelets and ted cells with the result that the method is capable of providing the CBC parameters RBC, HGB, HCT, MCV, MCHC, MCH, and PLT. The method can also count a sample s white blood cells if the sample s red blood cells have been lysed. 

A solvent free, fast and environmentally friendly near infrared-based methodology was developed for the determination and quality control of 11 pesticides in commercially available formulations. This methodology was based on the direct measurement of the diffuse reflectance spectra of solid samples inside glass vials and a multivariate calibration model to determine the active principle concentration in agrochemicals. The proposed PLS model was made using 11 known commercial and 22 doped samples (11 under and 11 over dosed) for calibration and 22 different formulations as the validation set. For Buprofezin, Chlorsulfuron, Cyromazine, Daminozide, Diuron and Iprodione determination, the information in the spectral range between 1618 and 2630 nm of the reflectance spectra was employed. On the other hand, for Bensulfuron, Fenoxycarb, Metalaxyl, Procymidone and Tricyclazole determination, the first order derivative spectra in the range between 1618 and 2630 nm was used. In both cases, a linear remove correction was applied. Mean accuracy errors between 0.5 and 3.1% were obtained for the validation set. 

The initial direction of transport of pollutants from their source is determined by the wind direction at the source. Air pollutant concentrations from point sources are probably more sensitive to wind direction than any other parameter. If the wind is blowing directly toward a receptor (a location receiving transported pollutants), a shift in direction of as little as 5° (the approximate accuracy of a wind direction measurement) causes concentrations at the receptor to drop about 10% under unstable conditions, about 50% under neutral conditions, and about 90% under stable conditions. The direction of plume transport is very important in source impact assessment where there are sensitive receptors or two or more sources and in trying to assess the performance of a model through comparison of measured air quality with model estimates. 

Critoph and Turner [15] carried out similar direct measurements for ammonia and 208C (coconut shell based) carbon manufactured by Sutcliffe Speakman Carbons. The bed conductivity was found to be around 0.165 W/mK at concentrations less than 20% and to rise to 0.19 W/mK at 25% concentration. The corresponding grain conductivities rose from 0.85 to 1.25 W/mK respectively. The higher grain conductivity than that found by Gurgel and Grenier may reflect the different structures present within the extmded and nut shell carbons. 

Kinetic data provide information only about the rate-determining step and steps preceding it. In the hypothetical reaction under consideration, the final step follows the rate-determining step, and because its rate will not affect the rate of the overall reaction, will not appear in the overall rate expression. The rate of the overall reaction is governed by the second step, which is the bottleneck in the process. The rate of this step is equal to A2 multiplied by the molar concentration of intermediate C, which may not be directly measurable. It is therefore necessary to express the rate in terms of the concentrations of reactants. In the case under consideration, this can be done by recognizing that [C] is related to [A] and [B] by an equilibrium constant ... 

The overall rate being measured is that of step 2, but there may be no means of directly measuring [ROH2+]. The concentration of the protonated intermediate ROH2+ can be expressed in terms of the concentration of the starting material by taking into consideration the equilibrium constant, which relates [ROH], [Br ], and [H+] ... 

Mass balance (C) should only be indicated it it is directly used to calculate the mass (weight) of chemical released. Monitoring data should be indicated as the basis of estimate only if the chemical concentration is measured in the wastestream being released into the environment. Monitoring data should flfll be indicated, for example, if the monitoring data relates to a concentration of the toxic chemical in other process streams within the facility. 

This gives a direct measure of the benefits obtained by the hood. In practice, the best way to determine the occupational hygiene efficiency is to measure the actual concentrations in the operator s breathing zone for those two cases. A tracer can also be used with the limitations described above. 

Direct measurement of conductivity is potentially a very sensitive procedure for measuring ionic concentrations, but it must be used with caution since any charged species present in a solution will contribute to the total conductance. 

Sherman compares calculated and observed intensities for a number of known samples in some of which the enhancement components predominate over the intensities by direct excitation. The agreement obtained is usually within a few per cent, and this would be satisfactory even for considerably simpler problems. To be sure, the calculations do not give concentrations from measured intensities. But the fact that intensities can be satisfactorily calculated from known concentrations means that absorption and enhancement effects are thoroughly understood, and that x-ray emission spectrography is on a firm foundation. 

EPR methods that allow a more direct determination of kv have been developed. These enable absolute radical concentrations to be determined as a function of conversion. With especially sensitive instrumentation, this can be done by direct measurement/57 160 An alternative method, applicable at high conversions, involves trapping the propagating species in a frozen matrix361 362 by rapid cooling of the sample to liquid nitrogen temperatures. 

In the absence of a direct measurement of the in-line concentration of solids ey. it is necessary to make an estimate of its value in order that the hydrostatic pressure gradient in the pipe may be calculated. This can be done for a given mixture velocity u and delivered concentration C, provided that the velocity of the particles relative to the liquid UR is known. 

Bonder, E.M., Fishkind, D.J., Mooseker, M.S. (1983). Direct measurement of critical concentrations and assembly rate constants at the two ends of an actin filament. Cell 34,491-501. 

Direct Measurement of HO, in the Troposphere. Techniques to measure tropospheric concentrations of HO have been reviewed (O Brien Hard, submitted to Advances in Chemistry, 1991) so only a summary will be given here. The most extensively researched technique for [HO ] measurement in the troposphere is based on laser-induced fluorescence (LIF) of HO. This approach has been developed in many configurations directing the laser into the free atmosphere and collecting fluorescence back scatter (LIDAR) (105,106,107) LIF of air sampled at atmospheric pressure... 

---