f. Predict how the van Deemter curve in Figure 7 would change if the temperature were raised from 40 °C to 55 °C. Figure 7. van Desmter curves in reduced coordinates for four nitroalkane homologues (nitropropane, black; nitrobutane, red; nitropentane, blue; and nitrohexane, green) separated on the FMS phase. Chromatographic conditions: column dimensions 50 mm × 4.6 mm id, eluent 30/70 ACN/water, flow rates 0.2-5.0 mL/min, injection volume 0.5 and column temperature 40 °C. No corrections to the plate heights have been made to account for extracolumn dispersion. Reduced Plate Height (h) ° 20 40 60 Reduced Velocity (v) 8. (2) A water sample is analyzed for traces of benzene using headspace analysis. The sample and standard are spiked with a fixed amount of toluene as an internal standard. The following data are obtained: Ppb benzene Peak area benzene Peak area toluene 10.0 252 376 Sample 533 368 What is the concentration of benzene in the sample?

When naphthalene, butyric acid, and phenyl acetate are separated using dichloromethane as the developing solvent on a silica gel TLC plate, which compound would have the highest Rf value?  Which would have the lowest?

2. Thin layer chromatography was performed to find the most effective mobile phase needed to separate a mixture containing three compounds (using silica gel as the stationary phase). TLC analyses were performed using five different mobile phases: (A) pure petroleum ether; (B) 25:75 ethyl acetate:petroleum ether; (c) 50:50 ethyl acetate:petroleum ether (D) 75:25 ethyl acetate:petroleum ether; and (E) pure ethyl acetate. Using the TLC results provided, indicate whether an effective separation was achieved for each of the five mobile phases. Be sure to provide a brief explanation for your answer and identify which mobile phase(s) could be used to offer an effective separation of this mixture using column chromatography. A D E

A mixture composed of biphenyl, benzoic acid, and benzyl alcohol is spotted on a silica gel TLC plate and eluted with a 10:1 hexanes:ethyl acetate solvent mixture.  In what order are the Rf values of the 3 compounds (lowest first)?