Analytical Chem istry - DePauw University

Chapter 7 Collecting and Preparing Samples341analysis. The following table shows results for a paint sample and for astandard reference material. Both samples and standards were digestedwith HNO 3 on a hot plate.Replicate% w/w Pbin Sample% w/w Pbin Standard1 5.09 11.482 6.29 11.623 6.64 11.474 4.63 11.86(a) Determine the overall variance, the variance due to the method andthe variance due to sampling. (b) What percentage of the overall varianceis due to sampling? (c) How might you decrease the variance dueto sampling?2. To analyze a shipment of 100 barrels of an organic solvent, you plan tocollect and analyze single samples from ten barrels using a random sampling.From which barrels should you collect samples if the first barrelis given by the 12th entry in the random number table in Appendix 14,with subsequent barrels given by every third entry? Assume that entriesin the random number table are arranged by rows.3. The concentration of dissolved O 2 in a lake shows a daily cycle fromthe effect of photosynthesis, and a yearly cycle due to seasonal changesin temperature. Suggest an appropriate systematic sampling plan formonitoring the daily change in dissolved O 2 . Suggest an appropriatesystematic sampling plan for monitoring the yearly change in dissolvedO 2 .4. The data in the following table were collected during a preliminarystudy of the pH of an industrial wastewater stream.Time (h) pH Time (h) pH0.5 4.4 9.0 5.71.0 4.8 9.5 5.51.5 5.2 10.0 6.52.0 5.2 10.5 6.02.5 5.6 11.0 5.83.0 5.4 11.5 6.03.5 5.4 12.0 5.64.0 4.4 12.5 5.64.5 4.8 13.0 5.45.0 4.8 13.5 4.9