Zeeman background corrector

An alternative procedure for the Zeeman background corrector is to operate the hollow cathode continuously but to expose the sample to an alternating magnetic field. The sample atoms absorb at the resonance line when not exposed to the magnetic field, but develop hyperfine structure and do not absorb the resonance line when the magnet is turned on. With the magnetic field on, absorption of the resonance line is a measure of molecular background. From the combined data, the net atomic absorption can be measured. 

In modem instruments background correction is carried out automatically. This is a dangerous simplification. Frequently the operator has no knowledge of the degree of background correction made which may be more than 90% leading to serious quantitative errors. Unsuspected problems are often concealed. The operator must be alert to detect these problems and correct for them by some other means. 

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Describe the operation of a Zeeman background corrector. Discuss its advantages and disadvantages compared with use of a deuterium lamp for... 

Background corrector Zeeman or deuterium arc. The Zeeman background corrector is recommended... 

Fortunately, methods for background correction are now a part of most modem AAS and the most commonly used background correctors are a deuterium source, the Zeeman effect and the Smith-Hiefte effect. 

Arsenic, selenium, and antimony can be measured at low concentrations with HG-AAS. Digestion with aqua regia in a microwave oven is necessary prior to the determination. Next, hydroxylammonium chloride is added as a neutral solution iodide may be added to accelerate the reaction. For arsenic or antimony a reducing agent such as ascorbic acid has to be added to convert all arsenic or antimony to a single oxidation state. A background correction is required for this purpose apparatus with a deuterium lamp corrector can be used but Zeeman background correction is preferred. 

A significant effort was necessary to obtain accurate results for selenium in blood, plasma, and erythrocytes [27]. Iron causes a spectral interference at the selenium line at 196 nm if a continuum source background corrector is used, causing erroneous results particularly in blood and erythrocytes. Zeeman effect background correction is therefore mandatory for the determination of selenium in clinical samples. In addition, some of the previously recommended chemical modifiers were found to stabilize the different selenium species differently, so that some of them may be lost in the pyrolysis stage. A mixture of palladium and magnesium nitrates was found to solve the problem and prevent any preatomization losses [28]. 

The determinations of gold are made by an atomic absorption spectrophotometer (Zeeman 5000, Perkin-Elmer) equipped with an electrothermal furnace atomizer (HGA-400) and with Zeeman effect background corrector. The operating conditions and the atomizer program for the spectrometer are listed in Table 3. 

M.-S. Chan and S.-D. Huang. Direct determination of cadmium and copper in seawater using a transversely heated graphite furnace atomic absorption spectrometer with Zeeman-effect background corrector. Talanta 51 373-380, 2000. 

Continuum correction often introduces overcorrection errors for particular combinations of matrix and analyte. Dozens of these errors have been summarized in the literature by Slavin and Carnrick (1988). Fig. 9 shows the problem that arises in tissue samples (fish in this case) when Se is determined. There is a large negative signal caused by phosphate absorption bands in the gaseous phase when a continuum corrector is used. The upper line is background. There is no problem when Zeeman correction is used. 

Copper is the only element commonly determined in the graphite furnace that suffers a significant loss of sensitivity (about 50%) when the Zeeman corrector is used. Nevertheless, this loss of sensitivity is more than compensated by the better background correction using the Zeeman effect. The Pd matrix modifier many improve the determination of Cu. 

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