chromatography homework

Q1 why the concentration of analytes has no potential effect on the retention time in GC and LC ?

Q2 Explain how the “B/u” term of the van Deemter equation contributes to band broadening? Why is it inversely proportional to mobile phase flow rate?

Q3 Gas chromatography was used to separate two similar compounds, methylcyclohexane and methylcyclohexene. A 40.0 cm packed column with OV-1 stationary phase (commercial liquid phase) generated the following results:

Base width (min.) Retention time (min.)

1.9 air (unretained

0.76 10.0 methylcyclohexane

0.82 10.9 methylcyclohexene

Calculate the relative retention (selectivity) factor for the two compounds.

Q4 Explain why high pressure liquid chromatography (HPLC) separations are generally characterized as having a higher efficiency than gas chromatography (GC) separations?

Q5 . Explain electroosmotic effect necessary for flow and separation in Capillary Electrophoresis (CE). What are the migration time trends for cations, anions, and neutral species?

Q6. How would the addition of an anionic surfactant above the critical micelle concentration affect the elution order of species in CE?

Q7 What is the electro-osmotic effect in capillary electrophoresis? Why do all species migrate to one electrode? Do they migrate to the cathode or the anode? What is the general order of migration time for cations, anions, and neutrals? Why are neutrals poorly resolved? (read the chapter related to this topic)