Background correction in AAS

Physical Interferences Chemical Interferences The Literature Interpolation Problem Ionization Interferences Spectral Interferences Spectral Interferences in Flame AAS Background Correction in AAS Spectral Interferences in Flame AFS Spectral Interferences in Flame AES Conclusions about Interferences... 

The use of the Zeeman effect for background correction in AAS was initially proposed in 1969 [23]. Six years later, the first commercial instruments became available [24]. Zeeman background correction is nowadays widely used in ET-AAS instruments. It is capable of reliably handling even high nonspecific absorption. In particular the more volatile elements Pb and Cd are preferably measured by ET-AAS with Zeeman background correction, since the relative volatility of the elements does not allow high temperatures to be used in the pyrolysis step to remove interferences. 

Cabon and Le Bihan [711] studied the effects of transverse heated AAS and longitudinal Zeeman effect background correction in sub xg/l determination of chromium, copper, and manganese in seawater samples. 

Zinc. AAS analysis of zinc by P CAM 173 is a standard application of the method as seen in NIOSH PAT. Zinc in the divalent state has been analyzed by dithiozonate (13). This colorimetric method suffers interferences from many other dithi-zone complexing metals. Zinc is easily determined after nitric acid wet ashing with an oxidizing air-acetylene flame using the 213.9 nm analytical line and background correction. The AAS analysis for Zn is as sensitive as more complex activation or plasma techniques. 

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. 

The last two decades have seen improvements of about four orders of magnitude in the sensitivity of atomic absorption techniques, due first to substantial improvements in graphite furnace atomization techniques and then to the introduction of Zeeman background correction. Flame AAS (F-AAS) methods are mainly of historical interest for all but the highest concentrations of Ni in biological solids. Furthermore, the pre-concentration and extraction procedures formerly required for determination of Ni in fluids can now... 

In addition, undissodated molecules, which may be oxides arising from the dissociation of ternary salts (MgO, ZnO, etc.), but also radicals and molecular species arising from solvent residues, such as OH, PO, SO2, etc., may cause non-element-specific absorption. In addition, Rayleigh scattering of primary radiation by non-evaporated solid particles may occur, which also leads to radiation losses. Both phenomena necessitate the application of suitable techniques for background correction in most analyses of real samples by furnace AAS (see Section 4.6). Furthermore, emission by the furnace itself may give rise to continuum radiation, which can lead to systematic errors. 

It should be stressed that background correction methods should always be used in furnace AAS. The background effect in this case may be as high as 85 per cent of the total absorption signal. 

The influence of matrix concomitants often cannot be recognised or quantified. Progress in background correction techniques (e.g. direct Zeeman-AAS [218]), furnace techniques, microweighing, and electronic signal processing have gradually made possible the elimination... 

Maximum power heating, the L vov platform, gas stop, the smallest possible temperature step between thermal pretreatment and atomisation, peak area integration, and matrix modification have been applied in order to eliminate or at least reduce interferences in graphite furnace AAS. With Zeeman effect background correction, much better correction is achieved, making method development and trace metal determinations in samples containing high salt concentrations much simpler or even possible at all. 

Knowles M (1987) Varian atomic absorption no AA 71 methods for the determination of cadmium in seawater with Zeeman background correction... 

Q. What are the advantages in AAS of (i) modulation, (ii) double-beam systems and (ill) background correction ... 

In a standard official method [50], the plant material is prepared for analysis by either digestion with 60% wlw perchloric acid, 70% wlw nitric acid, 1 3 mlv, and digestion of the residue with 2 M hydrochloric acid, or by dry combustion at 500 °C followed by extraction of the residue with 6 M hydrochloric acid. The concentration of nickel in these extracts is determined by AAS at 232.0 nm employing either background correction, or by an AA spectrophotometric procedure involving formation of the nickel ammonium pyrrolidiniedithio-carbamate followed by chloroform extraction. 

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