Quality assurance. Tin is leached (dissolved) into canned foods from the tin-plated

Chapter 20, Problem 20-24

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Quality assurance. Tin is leached (dissolved) into canned foods from the tin-plated steel can.33 For analysis by inductively coupled plasmaatomic emission, food is digested by microwave heating in a Teflon bomb (Figure 27-7) in three steps with HNO3, H2O2, and HCl. (a) CsCl is added to the final solution at a concentration of 1 g/L. What is the purpose of the CsCl? (b) Calibration data are shown in the table. Find the slope and intercept and their standard deviations and R2 , which is a measure of the goodness of fit of the data to a line. Draw the calibration curve. Emission Emission Sn (g/L) at 189.927 nm Sn (g/L) at 189.927 nm 0 4.0 40.0 31.1 10.0 8.5 60.0 41.7 20.0 19.6 100.0 78.8 30.0 23.6 200.0 159.1 (c) Interference by high concentrations of other elements was assessed at different emission lines of Sn. Foods containing little tin were digested and spiked with Sn at 100.0 g/L. Then other elements were deliberately added. The table shows selected results. Which elements interfere at each of the two wavelengths? Which wavelength is preferred for the analysis? Sn found (g/L) Sn found (g/L) Element added with 189.927-nm with 235.485-nm at 50 mg/L emission line emission line None 100.0 100.0 Ca 96.4 104.2 Mg 98.9 92.6 P 106.7 104.6 Si 105.7 102.9 Cu 100.9 116.2 Fe 103.3 intense emission Mn 99.5 126.3 Zn 105.3 112.8 Cr 102.8 76.4 (d) Limits of detection and quantitation. The slope of the calibration curve in part (b) is 0.782 units per (g/L) of Sn. Food containing little Sn gave a mean signal of 5.1 units for seven replicates. Food spiked with 30.0 g Sn/L gave a mean signal of 29.3 units with a standard deviation of 2.4 units for seven replicates. Use Equations 5-5 and 5-6 to estimate the limits of detection and quantitation. (e) A 2.0-g food sample was digested and eventually diluted to 50 mL for analysis. Express the limit of quantitation from part (d) in terms of mg Sn/kg food. 20-25.