Question: a. Describe the steps in QuEChERS and explain their purpose. b. Why is an internal standard used in QuEChERS? c. What is displayed in the

a. Describe the steps in QuEChERS and explain their purpose.
b. Why is an internal standard used in QuEChERS?
c. What is displayed in the total ion chromatogram in Figure 28-23?
d. What is displayed in the extracted ion chromatogram in Figure 28-23? What is the difference between an extracted ion chromatogram and a selected ion chromatogram? Which would have greater signal-to-noise ratio?
e. What mass spectrometric method could be used to obtain even greater signal-to-noise ratio from the same QuEChERS extract?

Figure 28-23

Total ion counts (105) 10 8 so 2 1 E Extracted ion

Total ion counts (105) 10 8 so 2 1 E Extracted ion counts 1 170 2 000 1 000 1180 Carfentrazone ethyl m/z 312 extracted ion 1 182 1 188 Wi 1 194 Total ion spectrum 1 190 Time (s) Harris/Lucy, Quantitative Chemical Analysis, 10e, 2020 W. H. Freeman and Company Extracted ion (m/z 312) opootrum 1200 1210 FIGURE 28-23 Partial gas chromatogram-time-of-flight mass spectrum of a pesticide extracted from a dietary supplement by QuECHERS. Column: 30 mx0.25 mm30 m x 0.25 m Restek Rxi-5Sil MS (0.25m thick), (0.25m thick), H:He 1.5 ml/min. 1.5 mL/min, 90-340C90-340C at 8/min./min, 70 ev 70 eV electron ionization, Iul. 1 splitless injection. Main spectrum is total ion count. Inset is m/z 312 m/z 312 extracted ion.

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