Ch. 10 Flashcards
(17 cards)
What is flash chromatography?
Flash chromatography is a method that uses pressure of air or nitrogen to force the mobile phase through the column
What spectroscopy method is used in this experiment to analyze the pigments?
UV/Vis
Out of lycopene and beta carotene, which will elute from the column first? Why?
Beta carotene will elute from the column first because it is more non-polar. It has less double bonds that will interact with the stationary polar phase. Lycopene has more double bonds that can interact with the stationary phase so it will remain in the column longer
What technique is typically combined with column chromatography to monitor the progress of purification?
TLC is typically combined with column chromatography to monitor purification progress. It helps identify which compounds are coming out of the column when comparing the sample to known standards.
What type of packing method will be used in this experiment? Why?
Dry packing will be used because slurry packing is typically used for macroscale operations.
What are some advantages and disadvantages to column chromatography compared to other purification techniques?
A: solids/liquids, large/small scale, collection/separation
D: most expensive, time consuming
What is the mobile and stationary phase used?
Mobile: non-polar - hexanes
Stationary: polar - alumina
What is the trend between polarity and elution time?
The more polar sample will be retained on the stationary phase longer so its elution time will be longest
What happens if the polarity of the solvent is changed too quickly?
The column can crack which will lead to poor separation
Why are methanol and water normally not used?
Water and methanol can destroy the integrity of the stationary phase by partially dissolving the silica gel
Which method achieves the best results? (dry/slurry)
Slurry
What are the two methods of dry packing?
- Fill the column with solvent first
2. Fill the column with stationary phase first (alumina only - silica expands)
Why should the column be packed as evenly as possible?
If the column is not packed evenly cracks, air bubbles, and channels will form which will lead to poor separation
Which method is used for macroscale separations?
Slurrry
What does it mean to let the column run dry?
If the solvent goes below the stationary phase it will run dry. This isn’t a good things because it allows air bubbles and channels to form - poor separation
Which type of chromatography is usually reverse phase?
HPLC - high performance liquid chromatography
How are enantiomers separated?
Chiral stationary phases can be used - only one enantiomer will be retained on the column - this is expensive and very specific
