Atomic absorption spectroscopy enhancement

Zinc in atomic absorption spectroscopy is remarkably free from interferences as contrasted to the difiiculties encountered in polarography or with colorimetric methods (M4). Gidley and Jones (G4, G5) studied the influence of 27 elements and the only effect seen was a depression with silicon. The absorption enhancement encountered by these authors with haloid acids could be traced back to the attack of the brass burner by the samples and to the use of a brass hollow cathode tube as zinc line source. Methods for the determination of zinc in various metals and alloys are described by these authors. 

Figure 6. This figure shows the depth distribution of Pb, Mo, and As in whole rock and insoluble-residue samples of rocks from borehole S-35 in the Ozark region. See Fig. 3 for the location of core S-35. The Pb (insols). Mo (insols), and As (insols) data are from emission spectroscopy analyses of insoluble-residues from the core. The Pb and Mo data are shown because these elements often correlate with As in midcontinent region rocks. The As (whole rock) column is data from whole rock analyses of the same depth intervals by Atomic Absorption Spectroscopy. The overall core interval spans the upper Cambrian and lower Ordo vician eras. The purpose of this plot is to show that insoluble residue data reflect, and even provide an enhanced distribution of As in rock column. The enhancement is because As is localized in the sulfide fraction that is concentrated in the insoluble residues.

Oscilloscope traces obtained from a 10 3M Ph2C-0 solution are displayed in Fig. 7.4. In catalyst-free solution, the 550-nm absorption of the ketyl decays as expected according to a second-order rate law. The rate constant obtained from the kinetic analysis if 8.5 x 10sM-1s 1 in agreement with published literature values. At the low laser intensity applied, this decay is barely visible on the 10-/is/division time scale in Fig. 7.4 a. Addition of catalyst, 8 mg of Pt/100 ml of solution as determined by atomic absorption spectroscopy, sharply enhances the absorption decay. This process follows approximately first-order kinetics, the half-life time being 40 /is. The decay is attributed to the reaction... 

Although the analyst may be unaware of its existence in the sample, signal suppression serves to decrease system sensitivity and raises the working detection limit. Spectral enhancement, on the other hand, increases the system sensitivity and lowers the working detection limit. "Enhancement is a well known problem in atomic absorption spectroscopy ( 12). A variety of approaches, such as Zeeman effect correction have been proposed for its elimination (11). To avoid artificially high results, calibration standards must contain concentrations of the enhancing species equivalent to those in the sample. Ordinary standard solutions are not representative of the analytical situation."... 

AAS = Atomic absorption spectroscopy. AFS = Atomic fluorescence spectroscopy. LEI = Laser-enhanced ionization. 

Early in the development of atomic absorption spectroscopy it was recognized that enhanced absorbances could be obtained if the solutions contained low-molecular-weight alcohols, esters, or ketones. The effect of organic solvents is largely attributable to increased nebulizer efficiency the lower surface tension of sueh solutions results in smaller drop sizes and a resulting increase in the amount of sample that reaches the flame. In addition, more rapid solvent evaporation may also contribute to the effect. Leaner fuel-oxidant ratios must be used with organic solvents to offset the presence of the added organic material. Unfortunately, however, the leaner mixture produces lower flame temperatures and an increased potential for chemical interferences. 

The mechanism of C02 reduction to methane at Cu electrodes has been proposed by various groups [72-74], most of which involved the splitting of adsorbed CO followed by the hydrogenation of surface C atoms. When DeWulf et al. used X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy to study the reaction [72], they observed surface-bound carbenes (Cu CH2) as an intermediate in the system. Likewise, others used both in situ infrared (IR) reflection absorption spectroscopy and surface-enhanced Raman spectroscopy to observe the initial product of C02 reduction on Cu [74]. Typically, two different linearly bound CO species were identified and attributed to adsorption on either surface defect sites or terraces. 

The photodissociation of bromobenzene in solution has been investigated with ultrafast transient absorption spectroscopy, following excitation at 266 nm. The main kinetic feature in acetonitrile was a 9 ps decay that was assigned to predissociation similar decays were observed in hexane, dichloromethane and tetrachloromethane. Laser-aligned iodobenzene have been photodissociated into phenyl radicals and iodine atoms with a 1.5 ps laser pulse at 266 nm, and the yield of iodine photoproducts detected by resonant multiphoton ionization." Significant yield enhancements were observed when the dissociation laser was polarized parallel instead of perpendicular to the alignment laser polarization. 

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