Amine analysis

[Bangkok34]

Hello,

I am trying to reproduce an old amine analysis method which determines monomethyl amine, dimethyl amine and trimethyl amine (non-derivatised). I have a couple of questions. They might seem trivial to you, but I have little GC experience so need to clarify.

1. I have always used capillary columns. This method uses a packed column which I must prepare myself by mixing two stationary phases such as Carbowax and Chromosorb. Is it still the way to do it or is there a capillary alternative to such analytical method? I would prefer to use a capillary column rather than making a column myself.

2. If I must use a packed column - can I fit it on my injector and detector inlet/ outlet - are they the same size for packed and capillary?

3. The method uses a hot wire thermal conductivity detector. Can I use an FID?

Thank you for your help and sorry for basic questions

B

[Don_Hilton]

The carbowax on chromaosob was a nice way to make a carbowax type column. You may bet getter result with a capillary column - so it is wort a try. FID should work for these compunds.

I woujld suggest taking a look at the catalogs put out by the column manufacturers, There are a number of carbowax type capillary columns and some modified for amine analysis. And a phone call to the applications support at a column manufacturer could lead you directly to the column you want.

In moving a method from a packed column to a capillary column, you will have to be careful of colulmn loading.

[chromatographer1]

Bangkok34

You are about to learn that one size does not fit all. I wish you luck with your attempts. Remember just as you would buy a capillary column from a vendor, you can also order a packed column from a vendor, and usually a lot cheaper.

Good luck,

Rod

[chromatographer1]

Bangkok34

A packed column comes in three sizes (sometimes more), 1/4", 1/8", 1/16" OD and different IDs.

They are not used in capillary inlet or detector configurations. Sometimes a 1/16" OD packed column can be used used with adapters in a capillary GC.

Since you do not know the difference in hardware configurations, I suggest you do not try to modify the capillary GC to work as a packed column GC.

Instead try a very thick film methyl silicone, or a base deactivated Wax column to perform your analysis from scratch. Remember that methylamine in an aqueous solution when heated in an injector or when allowed to stand at room temperature will form dimethylamine. Your analytical results may not be accurate over time it takes to do two injections.

Good luck,

Rodney George

[krickos]

Just to add on to what Rod and Don stated.

Have seen in an agilent catalouge those amines just separated with a 30m*0,53mm*5µm DB-1 column, headspace injection and FID detector at an isothermal temp of 30°C.

Some Wax capillary columns can be operated at 20°C but typically requires some cooling system installed. There are specail amine/wax columns such as the "CAM" column. Wax columns offer more polarity but phase is typically thinner than the methyl silicon options.

Also a question of my own: For very volatile amines can PLOT columns be used or is it impossible to get them inert enough?

[chromatographer1]

PLOT columns require a 'glue' to bind the polymer beads to the column surface. Hmmm, sticky glue, would that possibly be something an amine would 'stick' to? Possibly.

Rod

[Bangkok34]

Thanks a lot, everyone. Very useful info. I'll go through some column catalogues first. There must be a capillary column I can directly use.

Thanks
B

[Bangkok34]

The other question I have is that the old method which uses a packed column recommends a split injection of an aqueous solution of the amines. I know that aqueous injections are not a good thing for a GC but is it acceptable provided the samples are really clear of any salts, non-valatiles? I do not have a head-space set up and I will need to inject from a solution.

Thanks again

B

[chromatographer1]

A packed column using a porous polymer can tolerate hundreds if not thousands of water injections. The use of a splitter was due to the high volume of vapor created when water is heated in the injector port and due to the loss of sample capacity when a porous polymer is coated with the Wax liquid phase.

I have seen capillary columns using silicone phases degrade after only one injection of water. Carbowax phase capillary columns can take more than that, but are still damaged by water injections.

Capillary columns last longer if water is not allowed to remain as a liquid on the column phase. This amine analysis should really be done on a packed column. Do you have any access to a packed column GC?

best wishes,

Rod

[Bangkok34]

A packed column using a porous polymer can tolerate hundreds if not thousands of water injections. The use of a splitter was due to the high volume of vapor created when water is heated in the injector port and due to the loss of sample capacity when a porous polymer is coated with the Wax liquid phase.

I have seen capillary columns using silicone phases degrade after only one injection of water. Carbowax phase capillary columns can take more than that, but are still damaged by water injections.

Capillary columns last longer if water is not allowed to remain as a liquid on the column phase. This amine analysis should really be done on a packed column. Do you have any access to a packed column GC?

best wishes,

Rod

Thanks a lot for your help, Rod. I don't have an access to a packed column GC, but I guess could purchase one if really required.
Nevertheless I just found some application notes from Varian just on the analysis I need, i.e. analysis of MMA and TMA in DMA. The analysis is done in Methanol and the column they use is a capillary one - CP-Volamine with a film thickness of 5 micron. Not sure how sensitive to water this column is but the application notes show a water peak in TCD of 2000 ppm. So some water might be acceptable?

Thanks again

B

[chromatographer1]

If your sample's matrix is primarily water you may be disappointed with the capillary column you mentioned. The water peak will be so broad as to swallow up the methylamine peak. The main liquid in the chromatogram is not shown so it probably elutes later. Water and other peaks are listed as % levels. Due to the thinness of the water peak I can only assume that the amount is not a majority of the liquid.

Perhaps you could buy a micropacked Chromosorb 103 porous polymer SS column fused silica coating on the ID and use FS adapters for the injector and detector ports. You will have to get a 5µL syringe and inject 0.1-0.2µL or so samples, which would be a lot cheaper than a 60m capillary column.

best wishes,

Rod

[Bangkok34]

If your sample's matrix is primarily water you may be disappointed with the capillary column you mentioned. The water peak will be so broad as to swallow up the methylamine peak. The main liquid in the chromatogram is not shown so it probably elutes later. Water and other peaks are listed as % levels. Due to the thinness of the water peak I can only assume that the amount is not a majority of the liquid.

Perhaps you could buy a micropacked Chromosorb 103 porous polymer SS column fused silica coating on the ID and use FS adapters for the injector and detector ports. You will have to get a 5µL syringe and inject 0.1-0.2µL or so samples, which would be a lot cheaper than a 60m capillary column.

best wishes,

Rod

Thanks again Rod,

I will use FID so the water should not be detected as a peak right?

Anyway, my DMA is not in aqueous medium but comes in anhydrous form. I will have to use some kind of gas cylinder to dispense it into a flask containing a solvent. I guess I will have to use methanol or similar.

Thanks again...

B