Other concentration measures

The volume concentration in mol/1 is the typical concentration measure in spectroscopy as well as in kinetics. However, the transition to other measures may happen without problems. For example one finds for the relationship between a, and g,- (g/1)  

In this equation M, is the molecular weight of the compound A,. If one defines the diagonal matrix M with the elements M,., one can rewrite eq. (5.45) in the form 

The vector g is defined in analogy to vector a. Thus, using eqs. (5.42) and (5.46) one obtains for a single reaction time 

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Prepare a stock solution of 5 x 10 M in the complex in water. By dilution, prepare at least three solutions with other concentrations. Measure the absorbance at the wavelength of maximum absorption for the solutions. Plot absorbance against concentration and work out e in m mof. Prepare a saturated solution of the complex in water by sonicating a concentrated solution for 30 minutes after adding more solid until a residue remains undissolved at 25°C. Measure the absorbance of the supernatant at the same wavelength and hence calculate the solubility at 25 C. 

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. 

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. 

A diagnosis of possible damage should be made before beginning repairs with other construction measures [48,49]. There should be a checklist [48] of the important corrosion parameters and the types of corrosion effects to be expected. Of special importance are investigations of the quality of the concrete (strength, type of cement, water/cement ratio, cement content), the depth of carbonization, concentration profile of chloride ions, moisture distribution, and the situation regarding cracks and displacements. The extent of corrosion attack is determined visually. Later the likelihood of corrosion can be assessed using the above data. 

These equations hold if an Ignition Curve test consists of measuring conversion (X) as the unique function of temperature (T). This is done by a series of short, steady-state experiments at various temperature levels. Since this is done in a tubular, isothermal reactor at very low concentration of pollutant, the first order kinetic applies. In this case, results should be listed as pairs of corresponding X and T values. (The first order approximation was not needed in the previous ethylene oxide example, because reaction rates were measured directly as the total function of temperature, whereas all other concentrations changed with the temperature.) The example is from Appendix A, in Berty (1997). In the Ignition Curve measurement a graph is made to plot the temperature needed for the conversion achieved. 

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. ... 

Other O2 Measurement Techniques The oxygen concentration in the emission gases of combustion processes is often measured based on the strong paramagnetic character of oxygen. A sampling line with appropriate sample treatments is required with this method. 

An important principle is that security must be built in depth - otherwise known as defense in depth. In this context, it may be helpful to think of security as a set of concentric rings, where the target is located at the center. Each ring represents a level of physical protection (perimeter fence, building shell, security case) but the number of rings and security resistance will vary relative to the risk. The spaces between the rings may represent other defensive measures such as closed-circuit television (CCTV), security lighting, intruder alarm systems, etc. 

To determine the reaction rate at a given instant in the course of the reaction, we should make our two concentration measurements as close together in time as possible. In other words, to determine the rate at a single instant we determine the slope of the tangent to the plot of concentration against time at the time of interest (Fig. 13.4). This slope is called the instantaneous rate of the reaction. The instantaneous reaction rate changes in the course of the reaction (Fig. 13.5). 

Each concentration measure is convenient for some types of calculations but inconvenient for others. Consequently, a chemist may need to convert a concentration from one measure to another. Example illustrates the conversion from a mass-based concentration, percent by mass, to a mole-based concentration, molality. Mole... 

To convert between molarity and the other mole-based concentration measures, we must relate volume to mass and number of moles. Whereas molar mass lets us convert between mass and moles, we need density to convert... 

C12-0024. Prepare a table of the various solution concentration measures. Describe how to convert from each of them to each of the others. 

For acute symptomatic hypocalcemia, 200 to 300 mg of elemental calcium is administered IV and repeated until symptoms are fully controlled. This is achieved by infusing 1 g of calcium chloride or 2 to 3 grams of calcium at a rate no faster than 30 to 60 mg of elemental calcium per minute. More rapid administration is associated with hypotension, bradycardia, or cardiac asystole. Total calcium concentration is commonly monitored in critically ill patients. Under normal circumstances, about half of calcium is loosely bound to serum proteins while the other half is free. Total calcium concentration measures bound and free calcium. Ionized calcium measures free calcium only. Under usual circumstances, a normal calcium level implies a normal free ionized calcium level. Ionized calcium should be obtained in patients with comorbid conditions that would lead to inconsistency between total calcium and free serum calcium (abnormal albumin, protein, or immunoglobulin concentrations). For chronic asymptomatic hypocalcemia, oral calcium supplements are given at doses of 2 to 4 g/day of elemental calcium. Many patients with calcium deficiency have concurrent vitamin D deficiency that must also be corrected in order to restore calcium homeostasis.2,37,38... 

As in normal potentiometry one uses and indicator electrode versus a reference electrode, the electrodes should, especially in pH measurements, be those recommended by the supplier of the pH meter in order to obtain a direct reading of the pH value displayed. In redox or other potential measurements any suitable reference electrode of known potential can be applied. However, a reference electrode is only suitable if a junction potential is excluded, e.g., an Ag-AgCl electrode in a solution of fixed Ag+ concentration or a calomel electrode in a saturated KC1 solution as a junction in many instances a direct contact of Cl" with the solution under test (possibly causing precipitation therein) is not allowed, so that an extra or so-called double junction with KN03 solution is required. Sometimes micro-electrodes or other adaptations of the surface are required. 

Sample preparation is directed to the conversion of test samples in a physically and chemically measurable form. The measuring sample can require a definite state (gaseous, liquid, or solid) or form (aqueous or organic solution, melt-down tests, and pellets). In other cases, measuring samples have to become diluted or enriched to get an optimum concentration range. It may also be necessary to remove interfering matrix constituents which disturb the determination of the analyte. 

The next step in this study is to test this control algorithm on the actual laboratory reactor. The major difficulty is the direct measurement of the state variables in the reactor (T, M, I, W). Proposed strategy is to measure total mols of polymer (T) with visible light absorption and monomer concentration (M) with IR absorption. Initiator concentration (I) can be monitored by titrating the n-butyl lithium with water and detecting the resultant butane gas in a thermal conductivity cell. Finally W can be obtained by refractive index measurements in conjuction with the other three measurements. Preliminary experiments indicate that this strategy will result in fast and accurate measurements of the state vector x. 

In order to assess the accuracy of the present method, we compared it with two other methods. One was the Track Etch detector manufactured by the Terradex Corp. (type SF). Simultaneous measurements with our detectors and the Terradex detectors in 207 locations were made over 10 months. The correlation coefficient between radon concentrations derived from these methods was 0.875, but the mean value by the Terradex method was about twice that by our detectors. The other method used was the passive integrated detector using activated charcoal which is in a canister (Iwata, 1986). After 24 hour exposure, the amount of radon absorbed in the charcoal was measured with Nal (Tl) scintillation counter. The method was calibrated with the grab sampling method using activated charcoal in the coolant and cross-calibrated with other methods. Measurements for comparison with the bare track detector were made in 57 indoor locations. The correlation coefficient between the results by the two methods was 0.323. In the case of comparisons in five locations where frequent measurements with the charcoal method were made or where the radon concentration was approximately constant, the correlation coefficient was 0.996 and mean value by the charcoal method was higher by only 12% than that by the present method. 

B. Fixed level or supply rate Consists of periodic or continuous additions to prevent depletion of the compound. A fixed level can be maintained only when the concentration of the allelochemical can be measured during the course of the experiments. On the other hand, a fixed supply rate does not require concentration measurements. 

The PHSS method of real-time H2S measurement allows for investigating the potentially complex H2S kinetic responses of organs, tissues, cells, and mitochondria as levels of 02 and NO as well as metabolic state are adjusted within physiological limits. Kinetic changes in H2S concentration continuously reported by the PHSS, which are not seen with other H2S measurement techniques, suggest potentially complex interactions of H2S production and consumption mechanisms. H2S may likely exist as a cellular pool of free and labile persulfides able to rapidly respond to redox challenges with production and consumption pathways that operate to maintain the pool. This possible scenario reinforces the need for the PHSS as a valuable tool to provide a continual report of H2S throughout the course of an experimental treatment or to accurately determine H2S levels in situ. 

The Henry s law constant is essentially an air-water partition coefficient which can be determined by measurement of solute concentrations in both phases. This raises the difficulty of accurate analytical determination in two very different media which usually requires different techniques. Accordingly, effort has been devoted to devising techniques in which concentrations are measured in only one phase and the other concentration is deduced from a mass balance. These methods are generally more accurate. The principal difficulty arises with hydrophobic, low-volatility chemicals which can establish only very small concentrations in both phases. 

Maximum concentrations of chlordanes in American oysters (Crassostrea virginica) taken in the Gulf of Mexico in 1976 were near 0.1 pg/kg dry weight (Table 13.2). Chlordane concentrations were substantially lower than concentrations of other organochlorines measured in oysters, such as DDT (28 pg/kg) and polychlorinated biphenyls (90 pg/kg), suggesting a need for additional studies on interaction effects of chlordane residues with those of other environmental chemicals (Rosales et al. 1979). 

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