Absorption terminology

A variety of constants have been used to express absorption. All of these constants are based on the following general equation 

The ratio / // is obtained directly from a spectrophotometric measurement, and the value of a is then calculated from eq. (3.5) to yield the desired absorption constant. The numerous absorption constants found in the literature arise from the choice of quantities incorporated in the constant b. Some of the terms most commonly used to express absorption in minerals are summarized in table 3.2. Note that optical densities (O.D.), representing the direct output from many spectrophotometers, lack specificity about sample thickness and element concentrations. Absorption coefficients (a) indicate that sample thicknesses have been measured or estimated. Molar extinction coefficients (e) require chemical analytical data as well as knowledge of sample thicknesses. 

The assumption is made that absorption bands have Gaussian shapes, that is, they fit an expression of the form 

A fundamental relationship used in electronic absorption spectroscopy is the Beer-Lambert law which states that the amount of light absorbed is proportional to the number of absorbing molecules or ions through which the light passes. The Beer-Lambert law is formulated as 

The concentration, C, of a transition metal ion in solid-solution in a silicate mineral may be calculated from the mole fraction, X, and the molar volume, V, of the silicate phase by the equation 

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Several methods [17, 18, 29, 40, 62, 67, 223] for handling this design have been offered and each has introduced a concept to improve some feature. An approximation method combination of Kremser-Brown [40, 67] and a more complete method of Edmister [18] will be summarized. Figure 8-57 summarizes the system and terminology. The accepted nomenclature for absorption and stripping is located on page 121. 

Increase in mass-transfer rate per unit area. As stated above, agitated gas-liquid contactors are used, in general, when it is necessary to deal with sparingly soluble gases. According to the terminology of the film theory, absorption is then controlled by the liquid resistance, and agitation of the liquid phase could increase the mass-transfer rate per unit area. As will be... 

Modern terminology defines A as the absorbance, a as the absorptivity, b as the optical path length and c as the concentration. In the second equation s represents the molar absorptivity. Table 5.4 compares these terms. 

An introductory manual that explains the basic concepts of chemistry behind scientific analytical techniques and that reviews their application to archaeology. It explains key terminology, outlines the procedures to be followed in order to produce good data, and describes the function of the basic instrumentation required to carry out those procedures. The manual contains chapters on the basic chemistry and physics necessary to understand the techniques used in analytical chemistry, with more detailed chapters on atomic absorption, inductively coupled plasma emission spectroscopy, neutron activation analysis, X-ray fluorescence, electron microscopy, infrared and Raman spectroscopy, and mass spectrometry. Each chapter describes the operation of the instruments, some hints on the practicalities, and a review of the application of the technique to archaeology, including some case studies. With guides to further reading on the topic, it is an essential tool for practitioners, researchers, and advanced students alike. 

Chiou WL (2001) The rate and extent of oral bioavailability versus the rate and extent of oral absorption Clarification and recommendation of terminology. J Pharmacokinet Biopharm 28 3-6. 

The second law is the Stark—Einstein law. whose re-statement in current terminology is that the primary photochemical act involves absorption of just one photon by a molecule. This holds true for the vast majority of processes exceptions to it arise largely when very intense light sources, such as lasers, are employed, and the probability of concurrent or subsequent absorption of two or more photons is no longer negligible. 

In X-ray terminology, the term fluorescence may be used in the mure specific sense (than given in the general definition above) to denote the characteristic X-rays emitted as a result of Ihe absorption of X-rays of higher frequency. 

Functional property terminology is not well defined and is not universally agreed upon. Often, the same term is used to describe a variety of methods measuring different properties. For example, terms such as water hydration capacity, water absorption, water binding, and waterholding capacity are all used interchangeably to describe water bound or retained by a protein. It is therefore necessary to carefully define the terms under study and make sure the methods selected measure the desired parameters. 

Often instead of using state designations molecular orbital terminology is used to describe a transition (vide infra). To be consistent with the accepted convention for state symbols the higher MO should be written first (15). Thus the absorption of molecular hydrogen at 1100 A., -... 

Most Phase I oxidations are performed by cytochrome P-450. "Cytochrome," derived from Greek, literally means "colored substance in the cell." The color is derived from the properties of the outer electrons of the transition element iron. "P-450" denotes a reddish pigment with the unusual property of having its major optical absorption peak (Soret maximum) at about 450 nm, when it has been reduced and combined with carbon monoxide.330 Although the name "P-450" was intended to be temporary (until more was known about the substance), the terminology has persisted for 18 yr because of the increasing complexity of this enzyme system and because of the lack of agreement on new nomenclature. 

As an example, for styrene at 0°C. the following data are typical (30) rate of polymerization = 14.5%/hour, dose rate = 2.2 X 103 rads/hour, average DP 103. Since 1 rad corresponds to the absorption of 100 ergs/gram of material, it can be demonstrated, on the basis of the above values, that approximately 6 X 105 monomer units are incorporated into polymer for each 100 e.v. of energy absorbed. In conventional radiation chemistry terminology this would be expressed as G(.m0nomer)... 

The absorption-isotherm method provides a very useful approach to the study of a gas-solid system. Inflection points in the isotherms locate phase boundaries, and a plot of log P vs. 1/T (Arrhenius plot) permits calculation of heats of solution and estimation of the eutectoid temperature. The shape of the isotherms depends only on those phases which affect the hydrogen absorption, rather than all phases present. The actual phases present were identified by high-temperature x-ray diffraction. The designation of the phases follows terminology commonly used in U. S. Atomic Energy Commission studies ... 

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