9) If after drying, the TLC plate showed spot A showed a Rf of 0.20 and spot B showed a Rf of 0.22. This same plate was then placed back into the same developing chamber and allowed to develop a second time. Would you expect the distance between the A and 8 to increase, decrease, or stay the same? Why?

. Select the true statement(s) of the refractive index detector in HPLC? A. It is more sensitive than a UV detector B. It does not respond to many solutes C. It can only be used for isocratic elution D. All above is true

1. Describe the different types of analytes which can be analyzed using the different methods of optical analyses.  2. Why is it that absorbance readings be done at lambda max?

What is the purpose of chemically staining a TLC plate using iodine vapor?     To increase the Rf values of all compounds on the plate     To decrease the Rf values of all compounds on the plate     To visualize colorless compounds that react with iodine on the plate     To spread out the Rf values of all compounds on the plate more

Two compounds A and B from GC on two open tubular columns contains a XY-1 (100% methyl) and a XY-2 (50% methyl, 50% phenyl), with the same diameter, thickness and length under the same experimental conditions. The retention times and peak widths are show in the Table 1.Hint: phenyl groups interact more strongly with polar groups than methyl groups. Which compound is more polar? Explain your answer

With a purple dye combination and acetone as the solvent, a student conducts a TLC experiment on a silica gel plate. She gets a R of 0.89 for the blue spot and a R of 0.45 for the red spot. Describe the relevance of her findings.

Suppose triphenylmethanol and biphenyl have R¢ values of 0.30 and0.60, respectively, in a certain TLC experiment. Sketch the final appearance of a TLC plate, roughly to scale, including the starting line and solvent front a. for a pure triphenylmethanol sample b. for a triphenylmethanol sample contaminated with biphenyl

1. a)( b) ) List three factors that determine the rate at which compounds travel through a GC. In a TLC analysis, a student finds that all his spots have an R value less than 0.1. What should the student do to achieve a better separation?