Background correction, in atomic absorption

The Zeeman effect arises from the interaction of an external magnetic field ivith the magnetic moment of the emitting (direct Zeeman effect) or absorbing (inverse Zeeman effect) atom, resulting in split emission lines. This phenomenon has made a significant contribution to nonatomic background correction in atomic absorption spectrometry, especially in electrothermal AAS ivhere more serious nonatomic, nonspecific absorptions occur. 

Fernandez, F.J., Myers, S.A. and Slavin, W. (1980). Background correction in atomic absorption utilizing the Zeeman effect. Anal. Chem., 52, 741-746. 

Background corrections in atomic absorption are made similarly that is, by assuming the background absorption to be constant over several bandpasses. A nonresonance line emitted by the test hollow-cathode lamp or by another lamp is selected. This line (often an emission line of the filler gas) must be at least two band-passes from the resonance line of the test element. After checking to make certain that the test element does not absorb the chosen line, the absorbance of this line by the sample is measured and subtracted from the total absorbance at the resonance wavelength. 

Tl. Tarasevich, N, I., and Tsalev, D. L., Selection of nonabsorbing lines for background correction in atomic absorption analysis. Vestn. Mosk. Univ., Khim. 13, 242-244 (1972). 

Figure 20-15 Principle of Zeeman background correction for atomic absorption spectroscopy. (0) In the absence of a magnetic field, we observe the sum of the absorbances of analyte and background, (b) In the presence of a magnetic field, the analyte absorbance Is split away from the hollow cathode wavelength and the absorbance is due to background only, (c) The desired signal is the difference between those observed without and with the magnetic field.

Interferences in atomic absorption measurements can arise from spectral, chemical and physical sources. Spectral interference resulting from the overlap of absorption lines is rare because of the simplicity of the absorption spectrum and the sharpness of the lines. However, broad band absorption by molecular species can lead to significant background interference. Correction for this may be made by matrix matching of samples and standards, or by use of a standard addition method (p. 30 et seq.). 

CONTENTS Preface, Joseph Sneddon. Analyte Excitation Mechanisms in the Inductively Coupled Plasma, Kuang-Pang Li and J.D. Winefordner. Laser-Induced Ionization Spectrometry, Robert B. Green and Michael D. Seltzer. Sample Introduction in Atomic Spectroscopy, Joseph Sneddon. Background Correction Techniques in Atomic Absorption Spectrometry, G. Delude. Flow Injection Techniques for Atomic Spectrometry, Julian F. Tyson. 

Tens of elements can be measured in a single analysis. When a microcomputer is used, the results can be obtained automatically. It is possible to correct for background signals by simultaneously measuring several lines of one element. The linearity of the measurements covers a wider range than in atomic absorption. The optical part of these instruments is mounted on an ultra-stable metallic base. 

S. R. Koirtyohann, E. E. Pickett, Background correction in long path atomic absorption spectrometry, Anal. Chem., 37 (1965), 601. 

One new instrument is worthy of note. This is the Hitachi Zeeman effect atomic absorption spectrometer, model 170-70. It provides background correction for nonatomic absorption at all wavelengths through use of the Zeeman effect. It is presently offered only in a carbon furnace conflguration. The cost of the instrument is considerably higher than conventional instruments. 

In a single analysis, close to 20 elements can be measured rapidly. Correction of background noise is also possible by the simultaneous determination of several lines belonging to the same element. The linearity of the measurements extends over a broader range than in atomic absorption. 

All of the flicker noises can be effectively eliminated by the use of double-beam optics in conjunction with a background correction system such as Zeeman splitting or a well-aligned (or wavelength-modulated) continuum source. Thus the ultimate limiting noise in atomic absorption is source shot noise, which can be reduced (relative to total source intensity or I, ) by increasing the source intensity, up to the point of optical saturation. 

Dulude G (1992) Background correction techniques in atomic absorption spectrometry. In Joseph S (ed.) Advances in Atomic Spectroscopy, vol. 1. Amsterdam Elsevier. 

D. How is background correction accomplished in atomic absorption and atomic emission spectroscopy ... 

Other methods of background correction have been developed, including Zee-man effect background correction and Smith-Iiieffje background correction, both of which are included in some commercially available atomic absorption spectrophotometers. Further details about these methods can be found in several of the suggested readings listed at the end of the chapter. 

M HNO3. The concentration of Cu and Zn in the diluted supernatant is determined by atomic absorption spectroscopy using an air-acetylene flame and external standards. Copper is analyzed at a wavelength of 324.8 nm with a slit width of 0.5 nm, and zinc is analyzed at 213.9 nm with a slit width of 1.0 nm. Background correction is used for zinc. Results are reported as micrograms of Cu or Zn per gram of FFDT. 

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