Smith-Hieftje background correction method

With this technique, problems may arise with interference, such as background absorption—the nonspecific attenuation of radiation at the analyte wavelength caused by matrix components. To compensate for background absorption, correction techniques such as a continuous light source (D2-lamp) or the Zeeman or Smith-Hieftje method should be used. Enhanced matrix removal due to matrix modification may reduce background absorption. Nonspectral interference occurs when components of the sample matrix alter the vaporization behavior of the particles that contain the analyte. To compensate for this kind of interference, the method of standard addition can be used. Enhanced matrix removal by matrix modification or the use of a L vov platform can also reduce nonspectral interferences. Hollow cathode lamps are used for As, Cu, Cr, Ni, Pb, and Zn single-element lamps are preferred, but multielement lamps may be used if no spectral interference occurs. 

Background correction using a pulsed HCL (Smith-Hieftje method)... 

Background absorption can be compensated for or minimized by using sample-like standards or matrix modification, or by moving to an interference-free line if possible. However, the actual background correction methods are (i) Two line method (ii) Continuum source method (iii) Smith-Hieftje method (iv) Methods using the Zeeman effect. 

Pulsed lamp background correction A very simple method of background correction has been proposed by Smith and Hieftje [25] and is therefore known as the Smith—Hieftje method. It is based on the self-reversal behaviour of the radiation emitted by hollow cathode lamps when they are operated at high currents. This ef feet is seen when a large number of non-excited atoms are brought into the vapor phase. These atoms absorb the characteristic radiation emitted by the excited species. At the same time, a significant broadening of the emission line is observed. 

Other background correction systems include the Zeeman effect and the Smith-Hieftje background correction. A detailed description of the operational principles of these methods is beyond the scope of this chapter and the required information can be found in the relevant literature.7,13 The advantages of these methods over deuterium lamps are that high background signals (up to 2.0 units) and structured backgrounds can easily be corrected for. 

Smith, S.B. and G.M. Hieftje. 1983. A new background correction method for atomic absorption spectrometry. Appl. Spectrosc. 37 419 -24. 

The occurrence of molecular absorbance and scatter in AAS can be overcome by the use of background correction methods. Various types of correction procedures are common, e.g. continuum source, Smith-Hieftje and the Zeeman effect. In addition, other problems can occur and include those based on chemical, ionization, physical and spectral interferences. 

This self-absorption is the basis of the pulsed lamp technique for correction of the background absorption. Known as the Smith-Hieftje (S-H) method, this application uses a pulsed lamp which enables a comparison of the two measurements. In normal conditions (e.g. 10 mA) and with the sample into the flame, a global measurement representing the sum of the background absorption and the absorption of the element is observed, while under strained lamp conditions (500 mA) only the background absorption is present as the lamp will no longer emit at the wavelength chosen. The comparison of these two absorbance measurements leads, after correction, to the calculation of the absorption due to the sole analyte. 

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