Smith-Hieftje background

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... 

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. 

Figure 7 Schematic representation of how the Smith-Hieftje background correction system works. On the left, the source emits a simple, sharp line at low current, and both atomic and molecular absorption would be measured. On the right, this simple line has effectively been split by a pulse of high lamp current into a pair of lines at either side of the atomic absorption profile, and only molecular absorption or scatter would be detected...

Smith-Hieftje background correction uses a single hollow-cathode lamp pulsed with first a low current and then a high current. The low-current mode obtains the total absorbance, while the background is estimated during the high-current pulse. Read the interview at the beginning of Part V to learn more about Cary Hieftje and his work. 

The Smith-Hieftje background corrector has taken advantage of this self-reversal phenomenon by pulsing the lamp, alternating between high current and low current. At low current, a normal resonance line is emitted and the sample undergoes normal atomic absorption. When the HCL is pulsed to a high current, the center of the emission... 

Smith-Hieftje background correction First commercial ICP-MS instrument... 

Figure 79 The principle of the Smith-Hieftje background correction. The emission profile emitted by a hollow cathode lamp by using (A) low current, and (B) high current. (Adapted S. B. Smith, Jr. and G. M. Hieftje, Appl. Spectrosc., 1983, 37, 419)...

Discuss why background correction is necessary in AA. Distinguish between physical and chemical interferences in AA. Explain what is meant by the term Smith Hieftje background correction and discuss how it differs from the kind of correction employed in the Perkin-Elmer Model 3110 AA. 

Samples with high iron content may give too bw results when applying a deuterium background correction system (Van der Lee et al., 1987). In this case Smith-Hieftje background correction is necesserary. 

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