separation of acid, alcohols, alde with water

[nishasks]

we r analysing mix of acid, alcohol (etoh, buoh) with some quantity of water and aldehydes using Porapak Q column. Resolution of alcohols water is ok but acid (acetic acid n butyric acid) was not good.
we r having TCD
TCD 175C
Column 200C
Injector 150C
i tried many conditions also but not found the better one.
plz help me........................

Regards
N

[chromatographer1]

You did not state how you were injecting the sample and the type of column, whether capillary, packed, packed in glass, or in steel.

Free acids are not easy to chromatgraph by GC. And Porapak Q is not the best packing for free acids in any case.

If you have steel columns you should see a solution elsewhere.

If you are injecting on column, a glass column, then if the column is new and clean you may be able to get reasonable chromatography. If not, then you should try a column more suitable for free acid analysis, preferably with a carbon based packing or with a capillary column.

with so little info there is little more I can say.

best wishes,

Rod

[nishasks]

we r analysing mix of acid, alcohol (etoh, buoh) with some quantity of water and aldehydes using Porapak Q column. Resolution of alcohols water is ok but acid (acetic acid n butyric acid) was not good.
we r having TCD
TCD 175C
Column 200C
Injector 150C
i tried many conditions also but not found the better one.
plz help me........................

Regards
N

Thanx for Reply
I m using Porapak Q Steel Column
And injection volume is 0.2 microlit
Acid might be acetic n butyric acid
..................

[chromatographer1]

Use glass or fused silica columns.

Higher oven temperatures with steel columns will help but not solve your problems.

Good luck,

Rod

[Karen01]

I need to do a similar separation of EtOH, Acetone, isopropanol , n-propanol, butanol, acetic and butyric acids from aqueous solution... and i need to do all of that quickly (be able to inject every 10 minutes or less - which i think limits me to isothermal).

Any suggestions for a column to try?

Thanks,
- karen

[chromatographer1]

Column must be glass or fused silica lined SS, 80/100 Carbopack C/0.1% SP-1000 3 meters 80°C, maybe higher.

Or

80/100 Carbopack B/5% SP-1000 2 meters, maybe longer 90°C-110°C range, pick one.

If you were to pick a capillary, the of course, SPB-1000 would be the column of choice, megabore as thick a film as is available, but IPA and EtOH separation would be minimal or none.

If you delete the acids, then Porapak Q, 2m in fused silica SS tubing with screens, but only buy from Supelco unless you want voids in the packing that will ruin the separations. ( I no longer work for Supelco)

Isothermal at 190°C, less than 5 minutes. Getting acids as reasonable peaks is a problem if you want to separate them WITH the alcohols at the same time, isothermal and under 10 minutes SINGLE DIMENSIONALLY.

Multi-dimensionally is another horse of a different color.

best wishes,

Rod

[Karen01]

Thanks for the reply.

Column must be glass or fused silica lined SS, 80/100 Carbopack C/0.1% SP-1000 3 meters 80°C, maybe higher.

Or

80/100 Carbopack B/5% SP-1000 2 meters, maybe longer 90°C-110°C range, pick one.

And either of those will separate all those at once isothermally? I don't have a packed inlet, but maybe it's worth seeing if I can get one.

If you were to pick a capillary, the of course, SPB-1000 would be the column of choice, megabore as thick a film as is available, but IPA and EtOH separation would be minimal or none.

That lets that column out.

If you delete the acids, then Porapak Q, 2m in fused silica SS tubing with screens, but only buy from Supelco unless you want voids in the packing that will ruin the separations. ( I no longer work for Supelco)

In the past I've used a PoraPlot-Q capillary ... seemed to shed a lot of particles (FID spikes)... in any case i can't delete the acids.

Getting acids as reasonable peaks is a problem if you want to separate them WITH the alcohols at the same time, isothermal and under 10 minutes SINGLE DIMENSIONALLY.

That's what would be best if it's possible.

If I don't care about peak shape, as long as i can get a good calibration curve from the areas, is there a capillary column you think might work?

Thanks,
- Karen

[chromatographer1]

Your best bet is the reliable OV1301 phase capillary (aka DB-624 SPB-624) as the issue of ethanol, acetone, and IPA are well separated on a few columns but tail on many, and the water degrades the capillary.

How long, how many samples, etc will you be expecting to do this analysis?

Free acids DO NOT do well on most columns, and add water to the mix, well, it can get VERY expensive.

A micropacked column FS coated with screens (Supelco) won't require you to change your hardware.

PLOT columns lose particles and are NOT recommended.

A 1mm ID 1/16" OD column attached to a silcosteel 1/8" SS 2.1mm ID tube you should be able to inject 0.25µL without flash problems. Even more if you can attach it to a 1/4" tube.

Or you could use a short piece of megabore FSOT tubing in your capillary injector and attach it in the oven to a deactivated union and to the micropacked column using 5-10 cc/min flow rates, perhaps even more.

Good luck, but as I have said before, if it were easy.................................

Rod

[Karen01]

Your best bet is the reliable OV1301 phase capillary (aka DB-624 SPB-624) as the issue of ethanol, acetone, and IPA are well separated on a few columns but tail on many, and the water degrades the capillary.

I've used a DB-624 as well as DB-Wax for the alcohols, but from that experience i doubt the acids would elute isothermally in any reasonable timeframe on those columns.

How long, how many samples, etc will you be expecting to do this analysis?

For the foreseeable future probably between 60 - 100/day.... Which is why sample prep also has to be fast/simple.

Free acids DO NOT do well on most columns, and add water to the mix, well, it can get VERY expensive.

I was thinking of using headspace...I know from a different assay in a different life, from a much longer temperature programed run, I can get reasonable results for acids (R=0.998+ and RSDs < about 3%) using HS at these concentration levels, if I control pH. Running the HS oven at 60-70C would not put that much water on the column. The main issue is finding a column that will let me do all the analytes isothermally in 10 minutes or less.

Good luck, but as I have said before, if it were easy.................................

Thanks. Sounds like if I figure it out, it would be publishable.

[chromatographer1]

I find your comments quite believable. (not that I or anyone else would) It all depends upon the concentration (which you did not mention, probably with good cause.)

with a PE unit or a well deactived Agilent or Tekmar unit it may be possible.

I would really prefer to do a dual injection with dual column analysis with backflush.

Any chance at multidimensional?

I think it would be worthy of publication. BWDIK ?

best wishes,

Rod

[chromatographer1]

A Caveat

I anticipate that unless your adjustment of pH is done with a strong and non-volatile acid acid your recoveries of the acids will be non-linear. Do your validation carefully, with an emphasis on FULLY.

And I do wish you the best of luck,

Rod

[Karen01]

A Caveat

I anticipate that unless your adjustment of pH is done with a strong and non-volatile acid acid your recoveries of the acids will be non-linear.

In the past they were linear doing that.

And I do wish you the best of luck,

Thanks... It all hinges on finding the right column... and I do have an idea on something to try.

- Karen