TLC

Steps 4-7

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Steps 4-7 General Instructions
Step 4 Samples of the five known ketone-DNP derivatives dissolved in ethyl acetate are supplied.  We have only one set for the entire lab so:
  • Be sure not to contaminate the samples - use the capillary provided with each sample for that one only.
  • Don't leave the caps off;  keep them in the trays to avoid spills.
  • Leave them in the hood for all to use.
Step 5 Unlike mp capillaries, these microcapillaries are open at both ends.  Dip bottom in the solution to fill, and place a finger over the top end to hold sample in by vacuum (see below).
Step 6

The sample is applied as a small spot by touching the tip of the capillary to the plate.  Align the origin mark with one of the lines on the card, and use that as a guide.  

While gloves may appear to be a good idea, they are not advisable here. The latex makes an all-or-nothing seal at the top of the capillary - you will tend to get no spot or a large one.  The ridges of your fingertips make for a seal which is easier to adjust - it's much easier to spot precisely without gloves.
Step 7

©2001,2002 Daniel A. Straus

This shows a pretty good job of spotting a TLC plate.

The origin mark at the left and the spots are on the line which shows through the card.

Before developing, allow the plate to stand for at least 5 minutes so the spotting solvent fully evaporates.

NOTE:  You should practice spotting beforehand - the instructor should provide a few plates for this purpose......

Go forward to Steps 8-11