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Unformatted text preview: CEM 834 PROBLEM SET 6 Due at the beginning of class on Friday, December 9, 2005. FALL 2005 1. A solute with a partition coefficient of 2.95 is extracted from 10.0 mL of water into ether. a. b. c. d. e. What fraction of solute remains in the water after a single extraction with 20.0 mL of ether? What fraction of solute remains in the water after four equal extractions with a total volume of 20.0 mL ether? What fraction of solute remains in the water after an infinite number of equal extractions having a total volume of 20.0 mL? What volume of ether is needed to extract 99.0% of the solute in a single extraction? What total volume of ether is needed to extract 99.0% of the solute in four equal extractions? 2. Today, hidden explosives are detected in airports using ion-mobility spectrometry (IMS). Describe briefly (3 sentences or less) how IMS works and use your explanation to classify IMS as a separation technique with respect to the chemical potential profile (c, d, cd) and flow properties (S, F(=), F(+)) according to the scheme developed by Giddings. 3. Nitrated explosives can also be separated using capillary liquid chromatography with fluorescence quenching detection, as demonstrated by Goodpaster and McGuffin (Anal. Chem. 73 (2001) 2004-2011) and shown in the attached chromatogram. a. b. c. d. e. Calculate the plate number (N) for RDX, 2-am-4,6-DNT, and tetryl. Calculate the plate height (H) for RDX, 2-am-4,6-DNT, and tetryl. Calculate the retention factor (k) for 1,3-DNB, 1,3,5-TNB, and NB. The nonretained solute is labeled 0. Calculate the separation factor () for 1,3-DNB and 1,3,5-TNB and for 1,3,5TNB and NB. Calculate the resolution (Rs) for 1,3-DNB and 1,3,5-TNB and for 1,3,5-TNB and NB. 4. Detection of hidden explosives depends on the residue that remains on a surface or person after direct contact with an explosive material. Oxley and coworkers (J. Forensic Sci. 48 (2003) 1-9) investigated trends in explosive transfer by swabbing the hands of individuals handling the explosives as well as their workspaces. Given in the table below are masses (g) of residual TNT on swabs of the hands of 9 individuals that participated in the study, as well as swabs of the bench surface where the person had handled the explosives. ND indicates that the amount was too small to be determined accurately. Participant 1 2 3 4 5 6 7 8 9 a. b. c. d. TNT on hand swab ( g) 2.0 0.14 0.10 0.33 1.2 9.8 4.0 6.3 0.24 TNT on bench swab ( g) ND 2.0 5.0 ND 2.0 4.0 6.0 1.0 17 Calculate the mean and standard deviation of TNT recovered from each surface. Test whether the recoveries from the two surfaces have variances that differ at the 95% confidence level. Test whether the mean recoveries from the two surfaces differ at the 95% confidence level. The same study was conducted using RDX, another explosive material, and the data are summarized in the table below. Participant 1 2 3 4 5 6 7 8 9 10 RDX on hand swab ( g) 89 4 36 10 4 29 4 36 80 12 Determine if the mean explosive recoveries for the two explosives are the same at the 95% confidence level. Clearly state your null and alternate hypothesis. 5. The length, width, height, and mass of an unknown piece of metal were measured in order to estimate density. Volume of the metal was also measured by water displacement. The results below were obtained from repeated measurements. Length (cm) 5.98 5.67 6.06 5.80 5.92 5.77 a. b. c. Width (cm) 3.33 3.51 3.17 3.25 3.26 3.40 Height (cm) 4.02 4.11 4.08 4.25 4.15 3.97 Volume (mL) 81.45 79.65 78.90 80.25 80.50 81.05 Mass (g) 2.459 2.502 2.488 2.471 2.510 2.495 Calculate the mean and standard deviation of the length, width, height, volume, and mass of the piece of metal. Determine the volume from the measurements of length, width, and height. Use the propagation of error method to determine the standard deviation of the volume determined in part b. How does this compare to the standard deviation of the direct volume measurement calculate in part a? Explain or justify your conclusions. Using the volume with the least error, calculate the density of the piece of metal. Use the propagation of error method to determine the standard deviation of the density calculated in part d. d. e. Goodpaster and McGuffin (Anal. Chem. 73 (2001) 2004-2011) 0 1 2 6 5 7 8 9 10 11 13 Analytes (1) RDX (2) HMX (3) 1,3-DNB (4) 1,3,5-TNB (5) NB (6) 2-am-4,6-DNT (7) 4-am-2,6-DNT (8) 2,4-DNT (9) 2,6-DNT (10) 2-NT (11) 4-NT (12) 2,4,6-TNT (13) 3-NT (14) tetryl 12 14 4 3 Solution composition: 3.0 mg/mL of each analyte Column: 1.51 m x 200 m i.d. fused-silica capillary Stationary Phase: 5-m Shandon Hypersil C18 Mobile phase: 32.5% acetonitrile/water with 0.2 mM pyrene in acetonitrile added postcolumn Flow Rate: 3.8 L/min Temperature: 28 C Detection: Indirect fluorescence quenching: ex = 325 nm, em = 374 nm 0 60 120 180 240 300 Time (min) 360 420 480 ...
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- Fall '05
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