Analytical Chem istry - DePauw University

342 Analytical Chemistry 2.0Time (h) pH Time (h) pH5.5 4.2 14.0 5.26.0 4.2 14.5 4.46.5 3.8 15.0 4.07.0 4.0 15.5 4.57.5 4.0 16.0 4.08.0 3.9 16.5 5.08.5 4.7 17.0 5.0Construct a graph of pH as a function of time and suggest an appropriatesampling frequency for a long-term monitoring program.5. You have been asked to monitor the daily fluctuations in atmosphericozone in the downtown area of a city to determine if there is relationshipbetween daily traffic patterns and ozone levels. (a) Which of thefollowing sampling plan will you use: random, systematic, judgmental,systematic–judgmental, or stratified? (b) Do you plan to collect andanalyze a series of grab samples, or will you form a single compositesample? (c) Will your answers to these questions change if your goal isto determine if the average daily ozone level exceeds a threshold value?If your answer is yes, then what is your new sampling strategy?6. The distinction between a homogeneous population and a heterogeneouspopulation is important when you are developing a samplingplan. (a) Define homogeneous and heterogeneous. (b) If you collectand analyze a single sample, can you determine if the population ishomogeneous or heterogeneous?7. The sampling of a heterogeneous population is particularly challenging.Explain why you can minimize the sampling variance for a heterogeneouspopulation by increasing the number of samples, but not byincreasing the mass of individual samples.8. Beginning with equation 7.4, derive equation 7.5. Assume that theparticles are spherical with a radius of r and a density of d.9. The sampling constant for the radioisotope 24 Na in homogenized humanliver has been reported as approximately 35 g. 23 (a) What is theexpected relative standard deviation for sampling if you analyze 1.0-gsamples? (b) How many 1.0-g samples must you analyze to obtain amaximum sampling error of ±5% at the 95% confidence level?23 Kratochvil, B.; Taylor, J. K. Anal. Chem. 1981, 53, 924A–938A.