Specific absorbents

Because of the high rate of emission of alpha particles and the element being specifically absorbed on bone the surface and collected in the liver, plutonium, as well as all of the other transuranium elements except neptunium, are radiological poisons and must be handled with very special equipment and precautions. Plutonium is a very dangerous radiological hazard. Precautions must also be taken to prevent the unintentional formulation of a critical mass. Plutonium in liquid solution is more likely to become critical than solid plutonium. The shape of the mass must also be considered where criticality is concerned. 

Chlorophyll a and chlorophyll b are distinguishable by their typical spectral properties (Figure 6.1.lA). Each one shows a specific absorbance coefficient and E... 

Amotf was the first to develop a set of equations for acetone to simultaneously calculate chlorophyll a and chlorophyll b in 1949. Several authors later proposed different new equations based on more adjusted and accurate extinction coefficients due to the development of higher resolution spectrophotometers adapted to each special condition. Moreover, besides 80% acetone, coefficients for diethyl ether and ethanol were also established and their respective equations developed, as reviewed by Schwartz and Lorenzo and Eder. Solvents chosen should be those for which specific absorbance coefficients have been published to derive equations and updates should be carefully tracked for new values. 

Comparative studies of the widely employed spectrophotometric readings at the Soret and Q bands (405 and 630 nm, respectively) and the elemental analysis of copper and nitrogen showed that the spectrophotometric assay based only on the Soret band can overestimate the purity of a preparation. Erroneous data were attributed to an increase in absorptivity at the Soret band when other colored compounds like metal-free analogs and carotenoids are present. Indeed, copper-free chlorin e6 exhibits a specific absorbance 3.6 times greater than that of its coppered counterpart. Therefore, measurements at the Q band (630 mn) and the establishment of the S Q ratio are preferred. 

Fig. 20. Absorption spectra of CdS sols of different particle sizes Gower part) and the change in specific absorbance As at 300 ps after the pulse (upper part), mean agglomeration number (a) = 266, (b) = 94 2 )...

In reality, the adsorption of gas particles on a real surface can be simultaneously influenced by inhomogeneity of the surface and interaction between absorbed particles. Presumably, it is the nature of a specific absorbate-adsorbent pair that controls the major mechanism in each case. 

Exchangeable ions (EXC), sometimes including ions nonspecifically adsorbed and specifically absorbed on the surface of various soil components, such as carbonate, organic matter, Fe, Mn, Si, and Al oxides, and clay minerals. This part is controlled by adsorption-desorption processes. 

Figure 3.5 Three-dimensional display of the photodiode array absorbance data obtained by HPLC/PDA/MS for a M. truncatula extract. The first dimension is HPLC retention time, second is wavelength, and third is absorbance. The data can be rapidly previewed for specific absorbance regions characteristic of functional groups.

Carbon dioxide is absorbed in most anaesthetic breathing systems by means of a canister that contains a specific absorbing medium. This is often soda lime but may also be baralime in some hospitals. 

The role of ions in the tunneling process has received limited attention. By virtue of the limited size of the tunneling gap during atomically resolved imaging, completely solvated ions are unlikely to exist in the junction. In contrast, ions that are specifically absorbed on either the tip or... 

It is common, however, for liquid-phase systems to include many specific absorbing species. Such species could include isotopic variations, conformational isomers, and solvent-solute interactions resulting in varied-lifetime transient associations between molecules. Distributions resulting from these effects give the Voigt profile utility in studying liquid spectra. We must understand, however, that the functions introduced here are only rough approximations when applied to the spectra of liquids because of the complexities just mentioned and others beyond the scope of this work. 

We are going to reproduce the example studied in (ref. 19), where the term ts has been replaced by a given percentage of A. The mixture consisted of 0,7,5 and . isomers of hexachlorine-cyclohexane, for testing the method in known quantities. The absorption of the mixture was measured at 20 wavelengths, and the . isomer was regarded as the unknown component, responsible for the background absorption. Therefore, only the specific absorbances of the a,7 and 5 isomers were assumed to be known. 

To alleviate the burden of trying to prepare a potassium dichromate solution of exact concentration, the specific absorbance value cm can be used to compare the measured and standard values. The specific absorbance value normalizes the absorbance value obtained from using a solution of approximate 0.006% w/v to the equivalence of 1% concentration and a 1-cm path length measurement ... 

Acceptance. Typical accuracy 0.01 AU, or the specific absorbance value falls with the limit outlined in Table 10.9. Six replicate measurements of the 0.006% w/v potassium dichromate solution at 235, 257, 313, and 350 nm should be less than 0.5% RSD. 

The caseins may be quantified by densitometrically scanning polyacrylamide gel electrophoretograms (section 4.4.1) but more quantitative results are obtained by ion-exchange chromatography using urea-containing buffers. However, it should be realized that the specific absorbance of the individual caseins differs greatly (Table 4.2). 

The absorbance of 1% solutions of asl-, as2-, / - and /c-caseins at 280 nm in a 1 cm light path is 10.1, 14.0, 4.4 and 10.5, respectively. Since the protein concentration in eluates from chromatography columns is usually monitored by absorbance at 280 nm, cognisance should be taken of the differences in specific absorbance when calculating the concentrations of individual caseins in samples. 

Elimination of coextracted materials and concentration of tetracyclines have also been accomplished using mixed-phase extraction membranes with both re-versed-phase and cation-exchange properties (294,295), or solid-phase extraction columns packed with cation-exchange materials such as CM-Sephadex C-25 (301), aromatic sulfonic acid (310), and carboxylic acid (283, 300). For the same purpose, metal chelate affinity chromatography has also been employed. In this technique, the tetracyclines are specifically absorbed on the column sorbent by chelation with copper ions bound to small chelating Sepharose fast flow column (278-281, 294-296). 

In the pharmaceutical industry, medicines are standardized to a particular weight of active pharmaceutical per unit (for example, mg of substance per tablet), so the weight of a substance in a tablet, or volume of medicine, is of more interest than the number of moles. For most pharmaceutical preparations, then, we use the specific absorbance, A(l%, 1 cm), which is the absorbance (logio fo/f) of a 1% w/v solution (i.e. 1 g of substance in 100 cm solvent) in a 1 cm path length cell, in place of the molar absorptivity, e. This is the absolute method of substance identification, and the absorbance. A, can be related to T(l%, 1 cm) by equation (2.4) ... 

The electric field which actually affects the charge transfer kinetics is that between the electrode and the plane of closest approach of the solvated electroactive species ( outer Helmholtz plane ), as shown in Fig. 2.2. While the potential drop across this region generally corresponds to the major component of the polarization voltage, a further potential fall occurs in the diffuse double layer which extends from the outer Hemlholtz plane into the bulk of the solution. In addition, when ions are specifically absorbed at the electrode surface (Fig. 2.2c), the potential distribution in the inner part of the double layer is no longer a simple function of the polarization voltage. Under these circumstances, serious deviations from Tafel-like behaviour are common. 

Table F4.3.1 Wavelength Maxima (Amax) and Specific Absorbance Coefficients (a)a of Chi a and bfor Extracts in Different Organic Solvents...

The relationship between the molar absorbance coefficient (e) and the specific absorbance coefficient A %cm) is... 

In the case of enzymes involved in biochemical pathways, the isolation is often based on activity assays. The nature of the activity assay depends on the enzymatic reaction and can involve, for example, the detection of a product on a thin-layer chromatography (TLC) plate (see Chapter 4, Section 1.2.1), the appearance or disappearance of a specific absorbance in a spectrophotometric assay, or a coupled assay involving the oxidation or reduction of a co-factor such as nicotinamide dinucleotide (NAD(H)), which can be measured by changes in fluorescence. 

Campbell, D.H. (1 938a) The specific absorbability of protective antibodies against Cysticercus crassicollis in rats and C. pisiformis in rabbits from infected and artificially immunized animals, journal of Immunology 35, 205-216. 

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