Analytical Chem istry - DePauw University

634 Analytical Chemistry 2.0See Section 5C.3 in Chapter 5 to reviewthe method of standard additions.Example 10.12To evaluate the method described in Representative Method 10.4, a seriesof standard additions is prepared using a 10.0077-g sample of a salt substitute.The results of a flame atomic emission analysis of the standards isshown here. 19 added Na (mg/mL) I e (arb. units)emission intensity (arbitrary units)76543210-2 -1 0 1 2 3 4μg Na/mL0.000 1.790.420 2.631.051 3.542.102 4.943.153 6.18What is the concentration of sodium, in mg/g, in the salt substitute.So l u t i o nLinear regression of emission intensity versus the concentration of addedNa gives a standard additions calibration curve with the following equation.I e= 197 . + 1.37×µgNamLThe concentration of sodium in the sample is equal to the absolute valueof the calibration curve’s x-intercept. Substituting zero for the emission intensityand solving for sodium’s concentration gives a result of 1.44 mg Na/mL. The concentration of sodium in the salt substitute is144 . µ gNa 50.00 mL× × 250.0 mLmL 25.00 mL= 71. 9 µ gNa/g10.0077 gsample10G.4 Evaluation of Atomic Emission SpectroscopySc a l e o f Op e r a t i o nSee Figure 3.5 to review the meaning ofmacro and meso for describing samples,and the meaning of major, minor, and ultratracefor describing analytes.The scale of operations for atomic emission is ideal for the direct analysisof trace and ultratrace analytes in macro and meso samples. With appropriatedilutions, atomic emission also can be applied to major and minoranalytes.Ac c u r a c yWhen spectral and chemical interferences are insignificant, atomic emissionis capable of producing quantitative results with accuracies of between19 Goodney, D. E. J. Chem. Educ. 1982, 59, 875–876