K absorption

Use of glow-discharge and the related, but geometrically distinct, hoUow-cathode sources involves plasma-induced sputtering and excitation (93). Such sources are commonly employed as sources of resonance-line emission in atomic absorption spectroscopy. The analyte is vaporized in a flame at 2000—3400 K. Absorption of the plasma source light in the flame indicates the presence and amount of specific elements (86). 

Only k absorption bands reported as very strong are included (accuracy 10 cm ) (5,6). 

Sherwood, T. K., Absorption and Extraction, McGraw-Hill Book Co., Inc, New York (1937). 

IC = Clearance of impeller off tank bottom, in., Figure 5-34, equal to impeller (turbine) diameter, or 1C = D sometimes IC = % D is suggested K = Absorption coefficient... 

Wavelength shift of K absorption edge of sulfur, 37, 38 Weight-fraction , use, 164, 171 Window absorption, 45 Windowless counter tube, 55, 222 Windows, for electron beam, 177 for proportional counter, 55... 

Herman Pines and Luke A. Schaap The Use of X-Ray K-Absorption Edges in the Study of Catalytically Active Solids Robert A. Van Nordstrand The Electron Theory of Catalysis on Semiconductors Th. Wolkenstein... 

Figure 1. X-ray absorption spectrum of a silica supported ruthenium-copper catalyst at 100 K In the vicinity of the K absorption edge of ruthenium. Reproduced with permission from Ref. 8. Copyright 1980, American Institute of Physics.

Another limitation to the studies in Table 1 is the small number of plant species tested. Primarily monocotyledonous plants have been studied, although McClure et al. (26) found ferulic acid inhibitory in soybean. The restriction of studies to monocots is probably because the mechanism of mineral absorption has been more fully elucidated with monocots. Harper and Balke (32) reported some minor differences in the inhibition of K+ absorption by salicylic acid among oats (Avena sativa L.), wheat (Triticum aestlvum L.), barley, and maize roots. 

The short time periods (10 min to 4 hr) over which absorption was measured (Table 1) helps support the hypothesis that certain allelochemicals inhibit mineral absorption directly. Under acidic conditions (pH 4.0) salicylic acid inhibited K+ absorption within 1 min (32). The degree of inhibition remained constant over time when salicylic acid inhibited 1C " absorption (32) and when vanillic acid inhibited P0 absorption (28). Thus, at least phenolic acids appear to inhibit absorption rapidly and consistently. 

Two additional characteristics of the inhibition of mineral absorption by phenolic acids were observed. The inhibition of both P0 absorption (27) and K+ absorption (31, 32) was reversed when the phenolic acid was removed from the absorption solution. Harper Balke (32) found this reversibility to be dependent upon pH the lower the pH, the less the reversal. Also, kinetic plots of the inhibition of mineral absorption showed that the phenolic acids did not competitively inhibit either P0 (26, 28) or K+ (31) absorption. Rather, ferulic acid inhibited PO -absorption in a noncompetitive (26) or uncompetitive (28) manner and jr-hydroxybenzoic acid inhibited K+ absorption in an uncompetitive manner (31). 

Salicylic acid depolarized PD In epidermal cells of oat roots also. At pH 4.5, 500 pM salicylic acid caused a transient hyperpolarization followed by a dramatic depolarization to about -45 mV (Figure 2). Removal of salicylic acid produced a transient, partial repolarization. At pH 6.5, salicylic acid did not affect PD. These results with different pH s are consistent with the Influence of salicylic acid on K+ absorption in oat roots (32). 

It remains to be determined if one or both of these hypotheses are correct for plant roots. One feature of the inhibition of absorption by salicylic acid (and probably other phenolic acids) that may be relevant to this point is whether the neutral acid or the anion is responsible for the inhibition. In oat roots, the amount of neutral acid present when salicylic acid caused 50% Inhibition of K+ absorption was constant regardless of pH (Figure 6). However, the concentration of anion present changed several orders of magnitude. This result suggests the neutral acid is the species... 

Fig. 7. Electronic absorption spectra, d—d region, of Pt(II)Cl and Pt(IV)Cl in aqueous solution (from Jorgensen, C. K.. Absorption Spectra and Chemical Bonding in Complexes. London Pergamon 1962)...

Jorgensen, C. K. Absorption Spectra and Chemical Bonding in Complexes. Oxford Pergamon 1962. 

Position of the K-Absorption Limits of Vanadium in Its Compounds, Hendricks... 

K Absorption Edges of Potassium and Chlorine in Various Compounds, ... 

Jergensen, C. K. Absorption spectra and chemical bonding in complexes. London Pergamon Press 1962. 

Electronic Structure Determination, Cox and Beaumont have studied the polarized x-ray absorption edge of a single crystal of Zn 2 (23), in which the Zn has tetragonal (D ) site symmetry. The observed anisotropic K-absorption edges were explained in terms of a ls+4p and a ls-K4p, 4p ) transition. 

Figure 5.4 X-ray tube output spectrum, showing continuous emission and line spectra of the target material (in this case gold). The K absorption edges for major elements in silicate glasses are shown below the diagram, indicating that the gold M lines are particularly effective for the analysis of the light elements Na to P.

K-absorption edges in study of, 12 149 structure of, and magnetism, 3 27 Catalytic behaviors, metallic oxides, 29 240 Catalytic converter automotive, 24 71, 72 single-bed, 24 72, 74 design of, 24 75-77, 83-86 dual-bed, 24 73... 

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