10.7.1 First Column Chromatography experiment

When packed into a column and solutions are passed through them, various media changes the rates that the different constituents in the solution reach the end of the column through adsorption. 

Adsorption differs from absorption, in that instead of the absorbent being drawn into the body of the absorbent, it sticks to the outside of an adsorbent.

The different constituents in the solution washed through the column have different affinities for the adsorbents, so they reach the end of the column at different rates.

That allows us to separate those constituents into discrete samples, if we have a way to identify when the different changes occur, and a GC or HPLC to determine what is each sample.

Here is (Pharmer) Joe’s Oakes’ first simple 2013 DIY chromatography experiment using a column based on a 1 ½” X 36 sanitary tube.  It’s goal was simply to determine where the cannabinoids started and ended.

Joes first column

Joe's column chromatography test sled

Joe used flash grade silica for his media and Hexane to suspend it in (mobile).  He subsequently flushed the system using acetone, to prepare it for the next load.

To full the column, he mixed the silica into a slurry with Hexane and poured it into the column.  Once the slurry had drained so that there was room in the sight glass, Joe poured in his sample mixed at a 2:1 ratio with n-Hexane.

95% HPLC grade n-Hexane

Joe then replaced the top reducer/funnel with a cross, that had an in and out port, as well as one for a pressure gauge and one for a bleed valve.  The inlet was attached by tubing to the dip tube of a pressure tank of n-Hexane. 

Once N2 pressure was applied to the pressure tank, the bleed valve permitted the entrapped air in the hose and cross to be bled off, so only the Hexane and the sample are passing though the packed column.

 

Column with top cross mounted with ancillary pressure tank of Hexane

As the column separated the different constituents, and they reached the end of the column in their respective sequences, he determined when to separate the samples by observing the color bands form in the lower sight glass under UV light.

He ended up with 14 discrete samples, the first two of practically devoid of cannabinoids despite the purdy color and the last two, were devoid of cannabinoids.

14 Discrete samples from chromatography column

This preliminary experiment was not designed to identify the subtle differences in each of the samples, only to identify where the cannabinoids started and ended. 

The mono and sesqui terpenes were separated into the first two samples, with the cannabinoids starting with the third sample and continuing through sample 12 where the color dropped off and none detected in sample 13 and 14 which were flushed through with Acetone to clean the column for the next sample..

We used our SRI GC to analyze each sample, and below are pictures of the 1st discrete sample, the 3rd, 14th, and 13th.  Notice than the last two samples are so close that they got inadvertently reversed based on color.

1st, 3rd, 14th, & 13th Discrete samples


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