The description here is based on Goodney, D. Although each method is unique, the following description of the determination of sodium in salt substitutes provides an instructive example of a typical procedure. The best way to appreciate the theoretical and the practical details discussed in this section is to carefully examine a typical analytical method. Representative Method 10.7.1: Determination of Sodium in a Salt Substitute To accurately correct for these errors the analyte and internal standard emission lines are monitored simultaneously. In addition, the internal standard should be subject to the same chemical interferences to compensate for changes in atomization efficiency. To compensate for changes in the temperature of the excitation source, the internal standard is selected so that its emission line is close to the analyte’s emission line. The method of internal standards is used when the variations in source parameters are difficult to control. An increase in temperature of 10 K, for example, produces a 4% increase in the fraction of Na atoms in the 3 p excited state, an uncertainty in the signal that may limit the use of external standards. When using a plasma, which suffers from fewer chemical interferences, the calibration curve often is linear over four to five orders of magnitude and is not affected significantly by changes in the matrix of the standards.Įmission intensity is affected significantly by many parameters, including the temperature of the excitation source and the efficiency of atomization. \( \newcommand).Ī calibration curve for flame emission usually is linear over two to three orders of magnitude, with ionization limiting linearity when the analyte’s concentrations is small and self-absorption limiting linearity at higher concentrations of analyte.
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