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

Transcribed Image Text:

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 (0.25µm thick), (0.25μm thick), H:He 1.5 ml/min. 1.5 mL/min, 90-340°C90°-340°C 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.