Wrong direction of column

[punt]

Hi,

I got some question regarding the the flow direction of Packed Column.
Will Packed Column damage if after we re-install column in a reverse flow direction?

We are trying to analyze Hydrogen using Haysep Q column for back flushed join to a Molsieve 5A column. If the order is reverse, do we see a change in peak profile? like peak broadness and height? Is there any symptons which i can tell the order of the column is wrong?

Thank you

[Consumer Products Guy]

I won't try to be a smart-a$$ and say it will merge your peaks instead of separating them, like stirring backwards will "un-stir" a sample.

If the column is new/good shape, shouldn't matter. Each end has silanized glass wool to hold in the packing. In extremecases where the inlet-end of the packed column is crudded up, it may make a difference.

[chromatographer1]

I assume that you mean reversing each column front to back and not reversing the order of the two columns, putting the sieve column in front of the porous polymer column. That WOULD show a great difference.

Packed columns, especially made by those who are not especially careful and knowledgeable, may not be uniform in the density of the packing. One end of the column may be more tightly packed that the other. This will cause subtle changes in the chromatography if the column is reversed.

With porous polymer columns it is quite easy, in fact, almost mandatory if special techniques are not used, that the density of the packing will be less than optimal. When the column is conditioned, the shrinkage of the beads will cause voids in the packing which may vary in number from head to tail.

The beads also shrink with aging but much less than the initial shrinkage when first conditioned. These voids have great effect on the chromatography and cause tailing and broadening of the peaks. If their number is non-uniform through the column it can change the chromatography quite noticeably if the column is reversed.

Users (and I was one once) tend to assume perfection, especially when one pays good money for a product. Unfortunately, that is not always the case. If you have doubts, have you ever heard of an auto company issuing a recall of their vehicles?

If you are seeing a difference in your chromatography, it very well may be that the column you own does show the variability of head to tail reversal.

best wishes,

Rodney George
consultant and ol' time packed column maker

[punt]

Hi Rodney,

Thanks for your info, what i mean by reversing the column means sample going into Molsieve5A follow by Haysep Q, will it result in a different Hydrogen Peak shape and retention time?

Thank you

[chromatographer1]

Golly, there are a lot of conditional statements I could state, but

Yes, it will for retention time, and it certainly may, but not necessarily so, for peak shape.

It depends upon the condition of the column and the matrix of your sample, and the history of the columns as well.

You can ignore what I said above and accept the short answer:



YES.

Rod

[punt]

Hi Rodney,

Thank for the reply. Because I do not know which way is the correct direction for the inlet and outlet for the GC connection to the column. I try both way and inject pure H2.

On one way, the retention time is longer with broader and shorter hydrogen peak. And the other way shorter retention time with taller and sharper peak but the area remain about the same.

Based on the peak profile, are we able to tell which way is the correct order for the column?

Thank you

[chromatographer1]

I cannot answer any questions about what you can or cannot do, or what the analysis is supposed to do unless you tell me.



however,

I, IMHO, would suppose that if the hydrogen peak is shorter and wider that the sample went through the sieve column first, followed by the polymer bead column.

Now usually, the porous polymer column is meant to separate the H2 through methane from the CO2 and higher hydrocarbon analogs, which may be backflushed or may bypass the sieve column which is in a 'trap', using multidimensional chromatography terminology.

Injecting onto the sieve column would then be very, very wrong.

best wishes,

Rod

ps hint, hint

in the future do not remove the column tags from the column

[AICMM]

punt,

If this is a two column, one valve sequence reversal set-up, then CO2 in room air is the way to determine the column order. Start with a relatively short inject time (z.b. 0.5 min) and you should see atmospheric CO2 (barely, but it should be there.) If not, you probably have the sieve first. Be careful not to mistake a valve upset for a peak....

Best regards.

[punt]

Hi AICMM,

What u mean is if i inject without any samples, and atmospheric CO2 should be detected if the order for the column is Haysep Q first follow by molsieve5A?

Thank you

[chromatographer1]

MM means that if you inject air, and the mole sieve column is reversed to ahead of the HS column qicklky then CO2 in the air will pass through the HS column to the detector. Of course CO2 in air is less than 400 ppm, or 0.04% of the air balance.

air will also give you one peak through the HS column and two peaks throuigh the MS column.

best wishes,

Rod

[punt]

Hi Rodney,

If MolSieve column comes before HaySep column, wont the CO2 get retained on the MS column instead of passing through the HS column to the detector?

Or does MM mean inject air for 0.5 min then backflush so if HS column comes first, CO2 will be flush to the detector instead of going to MS column?

Thank you

[chromatographer1]

Since the timing of the valve operation can affect the results, here is what I suggest.

Save yourself some trouble and just pick one of the two columns and connect it from the injector to the detector, and bypass the valving altogether.

If the column is a MS you will get two peaks, O2 and N2 when you inject air.

If you get one peak then the column is the HS.

Then label the two columns. Troubles are over.

Rod

[punt]

Hi Rod,

Thanks for your help. But since i am using N2 as a carrier gas so if i inject air, can nitrogen still be detected?
I have manage to get other HaysepQ and a Molsieve 13X column to try out by injecting hydrogen. When the peak eluted from haysep Q only, the peak is taller and sharp.
But when join the Haysep Q to Molsieve, the peak eluted from Molsieve is broader and shorter but area remain about the same.
What could be the reason?

Thank you

[chromatographer1]

The pores on the Hayesep Q are 10 times larger than the pores on the Mole sieve 13X. The smaller pores allow the H2 to reside longer than bigger pores, thus more diffusion, thus a wider peak.

So the H2 is sharper on the HS column, assuming the MS is about the same length.

Rod