THIN LAYER CHROMATOGRAPHY
Q: Should I draw a line all the way across the plate at the origin?
A: No. Just make a pencil mark at one edge and use the line on an index card or piece of lined paper below the plate to align the spots. The reason is that any but the lightest of pencil marks will make a groove in the adsorbent layer, and can change the flow rate of solvent - this would be a real problem is it caused solvent to move faster in one area of the plate than the other.
Q: Do we keep the jar closed while developing the plate?
A: Yes - we want the atmosphere in the jar to be saturated with solvent vapor.
Q: My solvent front is uneven - what could this be due to?
A: Either you dropped the plate in rather than placing it slowly in the jar (causing solvent to splash on the plate) or you moved the jar. The jar should be left undisturbed during development and the solvent front should be a horizontal line. If not, the plate should be redone.
Q: I got a long smear on the plate, rather than a discrete spot. Why?
A: It sounds as if you overloaded the plate - try diluting your sample by about fivefold and running another plate.
Q: Do we develop all the way to the top of the plate?
A: No, stop a centimeter or two from the top. Don't forget to mark the solvent front before solvent evaporates.
Q: Can I develop the plate immediately after spotting?
A: You should wait about 5 minutes to let the spotting solvent dry. With some solvents (such as ethyl acetate) you can tell when this is by smell.
©2001,2002 Daniel A. Straus