ERSC-2230H • Environmental Sampling and Analysis
Assignment 03: Problem Questions (10%)
Answer all questions; remember to show your work. Submission deadline is Monday 22 March at 11:59 pm. It is recommended that you submit your assignment as a PDF rather than Microsoft Word to Blackboard (details and deadlines are also posted on Blackboard).
1. A wet sample of lake sediment contains 67% moisture. What is the dry weight of a 5 g wet sample?
2. The concentration of cadmium (Cd) in lake sediment digestate is 3 µg/L. If 5 g of dry sediment was used, and the total digestate volume is 25 mL, what is the Cd concentration in sediment?
3. A 0.5 g sample of moss was digested in 10 mL of nitric acid, and then diluted by a factor of 25. The solution was analysed by ICP-MS and found to have a lead concentration of 25.9 µg/L. What was the concentration of lead in the moss sample?
4. Sediment from Little lake, with a 70% moisture content, was digested with nitric acid and analysed for copper (Cu) by ICP-MS. The concentration of Cu in the sediment digestate was 652.0 µg/L. If 0.5 g of wet sediment was used, and the total digestate volume was 50 mL, (a) what is the Cu concentration in dry sediment in Little lake? and (b) does the concentration exceed the Canadian Sediment Quality Guidelines for Cu, which is 197 mg/kg dry weight?
5. A 25 mL lake sediment digestate is spiked with 0.525 µg of Cd. The measured Cd concentration in the sediment is 0.04 mg/L. The measured concentration in the spiked sample is 0.06 mg/L. What is the recovery?
6. A 0.5 g sub-sample of lake sediment was digested in 10 mL of nitric acid, and then diluted by a factor of 25. The solution was analysed by ICP-MS and found to have an Arsenic concentration of 9.365 µg/L. A second 0.5 g sub-sample of lake sediment was spiked with 10 µg of Arsenic and digested in 10 mL of nitric acid and diluted by a factor of 25. The spiked solution was analysed by ICP-MS and found to have an Arsenic concentration of 37.46 µg/L. (a) What is the recovery (%) of the spike? (b) What is the apparent and true concentration of Arsenic in the lake sediment in mg/kg? (c) If the sediment had a moisture content of 40% what would be the apparent and true concentration?
7. Using an Ion Chromatograph, you measure a chloride peak area of 96 mS*min, what is the concentration (mg/L) of chloride based on the following chloride calibration analysis? Remember to blank correct the standards (STD)! Calibration Standard Concentration (mg/L) Peak Area (mS*min) STD 0 0 2.8 STD 1 0.5 73.8 STD 2 1 147.6 STD 3 5 652.8 STD 4 10 1366.9
8. Using an Ion Chromatograph, you measure the chloride peak area in one sample three times (triplicate analysis), the measurements are: 582.6, 549.3 and 598.1 mS*min. Using the calibration equation from question 11, estimate the average chloride concentration (mg/L) in the three replicates and the precision of the analysis.