The Smith-Hieftje technique

Similar to Zeeman AAS, the Smith-Hieftje technique can be used for lines over the entire spectral range, and uses only one primary radiation source, so that alignment and stability are optimum. The technique is simple and much cheaper than Zeeman AAS. It does not suffer from limitations due to Zeeman splitting of molecular bands. However, as self-reversal is not complete, the technique can be used only for rather low background absorbance, sensitivity is decreased as the... 

Maia et al. [332] eliminated interferences in the direct determination of Hg in powdered coal samples by means of analyte transfer during the pyrolysis step from the platform to a graphite tube wall. This graphite tube was permanently modified with Pd, and detection limits in the range of 0.025-0.05 pg/g were obtained. In simultaneous multi-element determinations of Cu, Cr, Al, and Mn in urine, Pd was also very successfully used as a matrix modifier [333]. The use of Pd as a modifier, and also in combination with dynamic background correction techniques such as the Smith-Hieftje technique (see Section 4.6.3), enables a considerable enhancement of the analytical accuracy of AAS, as shown in the case of As determinations [334]. 

In the previous section it has been shown that the measured sample absorbance may be higher than the true absorbance signal of the analyte to be determined. This elevated absorbance value can occur by molecular absorption or by light scattering. There are three techniques that can be used for background correction the deuterium arc the Zeeman effect and the Smith-Hieftje system. 

Another type of background correction system that has found some use is that developed by Smith and Hieftje. The Smith-Hieftje background correction technique is of especial use when there is strong molecular interference, such as that observed by phosphate on selenium or arsenic determinations. If the hollow-cathode lamp is run at its normal operating... 

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. 

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. 

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