A thought from my past that I never followed up on: A problem with separation of say two compounds is that they do not travel down the column as disks but as cones, caused by laminar flow constraints. My idea was, can you place a glass rod in the middle of the column and minimize the conization, producing more of a doughnut shaped eluent which would not overlap with other doughnuts as much as cones would overlap with cones. Just speculating...
Thank you for the explanation! It helped me a lot to understand the effect of packing on column chromatography. I'd like to ask a question. Let's say you load dry sample and it's in 20mL silica. (The diameter of the column is about 10 cm.) Then how long silica packing should be? I'm not sure how long silica packing is the best for efficient separation of compound.
several matters to clear up. your adsorbent is shown to be the same size. is this true in practice ? i'd thought silica gel came as a range ex. 60 - 100 mesh. and for a column being dried. does this imply it was once wet , and after some sample ran through it the column was set aside for use again later ? clear up if columns are re-usable. and what does it take to get it ready again . i presume this can be ok for an identical sample as last time. and thus one can save on adsorbent. $300 and up for 500g s. gel at this time.
Hi Bob. To clarify: First, adsorbents do indeed often come in a range of particle sizes. This is a consequence of the manufacturing process. Even those labeled as a single size such as "40 mesh or 60 mesh" obviously are reporting an average particle size. This is generally true but a bit too much detail for an introductory video on column technique, in my opinion. Second, by 'dried' I mean absent of solvent (not necessarily water). Many organic solvents cause stationary phases such as silica gel to swell or contract to a certain degree. When that solvent is suddenly removed, the rapid constriction or swelling of the column can cause irregularities to form. Columns can indeed be reused or even repacked if they become damaged. There are cases in which compounds can become permanently 'stuck' on the stationary phase if their affinity is too high, rendering it compromised, but generally columns can be reused many times over as long as they are washed of residual analyte materials using a mobile phase with strong eluting power before re-use. Thanks for the questions!
A thought from my past that I never followed up on: A problem with separation of say two compounds is that they do not travel down the column as disks but as cones, caused by laminar flow constraints. My idea was, can you place a glass rod in the middle of the column and minimize the conization, producing more of a doughnut shaped eluent which would not overlap with other doughnuts as much as cones would overlap with cones. Just speculating...
Thank you for the explanation! It helped me a lot to understand the effect of packing on column chromatography.
I'd like to ask a question.
Let's say you load dry sample and it's in 20mL silica. (The diameter of the column is about 10 cm.) Then how long silica packing should be?
I'm not sure how long silica packing is the best for efficient separation of compound.
It is a very nice demonstration. Thanks.
very good video.. thanks for the animations..
several matters to clear up. your adsorbent is shown to be the same size. is this true
in practice ? i'd thought silica gel came as a range ex. 60 - 100 mesh.
and for a column being dried. does this imply it was once wet , and after some
sample ran through it the column was set aside for use again later ?
clear up if columns are re-usable. and what does it take to get it ready again .
i presume this can be ok for an identical sample as last time. and thus one can
save on adsorbent. $300 and up for 500g s. gel at this time.
Hi Bob.
To clarify:
First, adsorbents do indeed often come in a range of particle sizes. This is a consequence of the manufacturing process. Even those labeled as a single size such as "40 mesh or 60 mesh" obviously are reporting an average particle size. This is generally true but a bit too much detail for an introductory video on column technique, in my opinion.
Second, by 'dried' I mean absent of solvent (not necessarily water). Many organic solvents cause stationary phases such as silica gel to swell or contract to a certain degree. When that solvent is suddenly removed, the rapid constriction or swelling of the column can cause irregularities to form.
Columns can indeed be reused or even repacked if they become damaged. There are cases in which compounds can become permanently 'stuck' on the stationary phase if their affinity is too high, rendering it compromised, but generally columns can be reused many times over as long as they are washed of residual analyte materials using a mobile phase with strong eluting power before re-use.
Thanks for the questions!
O chem HW brought me here...