Self-absorption, atomic spectroscopy

Because the atomic fluorescence is measured at a right angle to the source, spectral interferences are minimal and a simple cutoff filter may often be used to isolate the emission line. The intensity of the fluorescence is directly proportional to the analyte concentration. As the analyte concentration within the flame becomes large, self-absorption of resonance fluorescence becomes significant, as it does in flame emission spectroscopy. Under these conditions, the linearity of the instrumental response breaks down and a calibration curve must be used or the analyte solutions diluted accordingly. 

In flame emission spectroscopy, the concentration of electronically excited atoms in the cooler, outer part of the flame is lower than in the warmer, central part of the flame. Emission from the central region is absorbed in the outer region. This selfabsorption increases with increasing concentration of analyte and gives nonlinear calibration curves. In a plasma, the temperature is more uniform, and self-absorption is not nearly so important. Table 20-4 states that plasma emission calibration curves are linear over five orders of magnitude compared with just two orders of magnitude for flames and furnaces. 

It is now fairly well established that atomic and few-atom cluster arrays can be generated and trapped in weakly interacting matrices 91), and subsequently scrutinized by various forms of spectroscopy. Up to this time, IR-Raman-UV-visible absorption and emission-esr-MCD-EXAFS-Mossbauer methods have been successfully applied to matrix-cluster samples. It is self-evident that an understanding of the methods of generating and identifying these species is a prerequisite for... 

D. Wienke, T. Vijn and L. Buydens, Quality self-monitoring of intelligent analyzers and sensor based on an extended Kalman filter an application to graphite furnace atomic absorption spectroscopy. Anal. Chem., 66 (1994) 841-849. 

Zsila, F., Z. Bikadi, Z. Keresztes, J. Deli, and M. Simonyi. 2001b. Investigation of the self-organization of lutein diacetate by electronic absorption, circular dichroism spectroscopy, and atomic force microscopy. J. Phys. Chem. B 105 9413-9421. 

Tncreasing national concern over the ecological and environmental effects of coal combustion coupled with the desire to become more self sufficient in mineral production led the Coal Research Bureau at West Virginia University to examine the major and minor constituents in coal ash. Because of the need for accurate results at the low trace element concentrations, it was felt that atomic absorption spectroscopy could provide a rapid and routine method for analytical determinations. 

It has been found, however, in practice that a perfectly straight analytical working curve (— log T plotted against concentration) is seldom obtained in atomic absorption spectroscopy. The reasons for this are usually a combination of instrumental problems broadening of the emission line of the light source due to self-reversal, Doppler and pressure broadening of the absorption lines of the atoms in the flame, failure to exclude flame emission entirely, use of a focused instead of a parallel... 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

In further studies, the self-doping mechanism of these polymers was verified by cyclic voltammetry, pH measurements and atomic absorption spectroscopy [17,20]. The cyclic voltammograms of the sodium salt and acid forms of poly(3-thiophene butanesulfonate) cast films are shown in... 

Preliminary investigations of self-doped polythiophenes did not specify whether the cation species associated with the sulfonate group was expelled or whether an additional anion was incorporated during electrochemical oxidation of the polymer. Using cyclic voltammetry, pH measurements, and atomic absorption spectroscopy, it was established that the hydrogen ion associated with poly(cu-(3-thienyl)alkanesulfonic acids... 

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