Chromatography Forum

Hi guys,
I'm new to the forum and relatively new to GC/MS chromatography. I am currently working on a Shimadzu GC-2010 paired with a GCMS-2010 mass spec. I have several unknowns that I wish to analyze and I am exactly sure of what type of protocol or column to use. The unknown is a wax, very similar to beeswax but slightly lighter in color. I would guess there is beeswax, perhaps crisco, beef tallow, etc in the sample and maybe even molybedneum or graphite. I have the following supelco columns to choose from:

Supel-Q
Nukol
SPB-1 sulfur column
Omegawax 530
Equity-5


Also, i am not sure of exactly what solvent to use. I was thinking perhaps toluene or chloroform as I believe these would dissolve the sample nicely. I have SPME capability as well as liquid injection capability. I would prefer to use the SPME however. Could anyone give me a basic protocol (temp program) to use for the GC/MS to obtain good seperation? I appreciate any help you can give me!
Thanks,
Ruck

What are you looking for in your unknowns? Volatiles, PAHs, etc.?

I think i'm looking for mostly volatiles. I would guess most of them are alkane/alkenes, both saturated and unsaturated but I am not exactly sure of exact content. Thanks for the quick response.
Ruck

Hi, for your solvent, avoid using Chloroform if you can help it because it is not used much in industry now due to its environmental effects.

Regards,

Salma

I realize that chloroform presents several hazardous waste issues however I can dispose of it easily. Any other suggestions on solvent to use other than chloroform?

Hexane and methylene chloride work well when I need to dissolve fats/lipids/waxes. However, I think the hexane may interfere with your analysis.

For a temperature program for volatiles, I would start at 40°C for 3-10 minutes, then ramp at 3-8°C/min to your column's max temp and hold for 5-10 minutes. You can work from there after you identify the peaks you want to focus on.

Any column will work (1, Wax/624, 5). I would go for a narrow bore and thin film because of the MS. Again, once you determine your analytes and selectivity, you can go to a more suitable column to optimize run time and separation. I usually work with older columns, so I don't worry about cost and wreckin' them.

If you are looking for solvent (volatiles) then don't use any solvent at all.

You should be using headspace, with or without SPME. If you have a static headspace analyzer, all the better.

Simply heat and melt the wax like matrix in a headspace vial and you will place any moderate boiling point or low boiling point components into the headspace. Then sample (SPME works well for this) and you can ID these by MS, preferably on an Equity 5 column.

Once you know what volatiles to look for ( probably hexanes/hexenes, possibly methylene chloride or ethyl acetate ) you can prepare suitable methods to measure the amount of residual solvent.

And it won't take much sample to perform the initial screening test, perhaps only 1 - 5 mg of material to see low ppm levels of solvent.

best wishes,

Rod

Hi Ruck,

Can you tell us what the origin of the sample is?

After you done the headspace you can dissolve some sample in toluene (that will take up beeswax) and run it on the same Equity-5 column but be prepared to have a long final time if it is beeswax. Beeswax has a load of easily identifiable characteristic wax esters in it.

Another option is to split the sample into saponifiable and non-saponifiable material. The saps can be further treated to analyse for the fatty acid distribution to help you identify any fats present. The non-saps would contain any waxes and you can determine the amount gravimetrically. If this is the sort of identification that you are after I can post up the procedures.

Regards,

Ralph

The origin of the sample is actually a "lube" applied to bullets. It is melted down and then applied to each individual cast bullet. This in turn softens the fouling in the barrels of rifles. At room temp, the lube is solid and I'm guessing probably doesn't liquidify until about 120*F (roughly 48*C).

That method that you detailed GOM would perhaps help very much. I need to find out what is in this stuff as it is going to quit being made and I am relatively sure that I can match it if I know what's in it. I am positive that all of the stuff in it is relatively easy to come by as it is made by a guy in his garage. I know it sounds rather crude but this is the best stuff around for this type of thing.

I greatly appreciate any help that you can give me. As i mentioned, i'm relatively new at all of this.

Oh yeah, before i forget, i would prefer to use SPME for headspace analysis.

Simon

It could be a molybdenum grease with some graphite added. It might even be made from Teflon or Krytox components, or even High Mole Wt PEG.

I would perform size exclusion HPLC to determine the approximate Mole Wt of the grease and do a metal analysis to determine any additives. If it is made in a garage it must be made from commercially available materials.

A short 3 to 5 meter Equity 5 or similar column after dissolving the grease in hexane or toluene might be useful to determine the carbon number if you have standards to run against.

If your supplier is going out of business, have you tried to get the information from him? This would save you a lot of work. Perhaps you can get the receipe?

best wishes,

Rod

Hi Simon,

Yes, you get so tied up with enjoying solving the problem you forget simple things like "just ask him"

The procedure for nonsaponifiables (if I remember correctly) is
1. Weigh out 2 g of sample
2. add 25mls 0.5M KOH in methanol - this saponifies any fat
3. reflux for 60mins
4. cool and transfer to a separating flask
5. add 50mls of water
6. extract with 100mls diethyl ether
7. extract with two further 50ml portions of ether
8. combine the ether extracts and backwash with 50mls water.
9. transfer the ether extract into a weighed flask containing antibumping granules and evaporate off the ether
10 add 2mls acetone, evaporate off to constant dryness
11. reweigh the flask which now contains any waxes
12. If it's 100% then there is no triglyceride material like tallow fat

13. If it's not, then acidify the aqueous portion with 2M sulphuric acid. This converts the potassium soaps to the free fatty acids.
14 extract with the fatty acids with ether and dry.
15. Run as is or convert them to the fatty acid methyl esters. Tallow will be mainly C16/18
16. Alternatively, for steps 13 - 15 use a transesterifcation method - see previous posts. - or just assume that it is tallow fat

Keep an eye out for any fine black solid material in the aqueous layer that may graphite.

If the non-sap is a mixture of pet.jelly, paraffin wax and beeswax it can be very tricky to pull apart. Beeswax has some characteristic wax esters, paraffin wax has a nice alkane distribution but pet.jelly has an awful unresolved hump because it is such a mix of branched and unsats.

Regards,

Ralph

Hi Ruck

You are proposing to throw huge analytical resources at a deformulation / reverse engineering problem. It would be more cost effective by far to buy the recipe from the present manufacturer - if the lube is going out of production the price should not be too high.

Peter

I suspect that equivalent formulations will be available from many shooting enthusiasts, if the current owner doesn't relinquish it..

GC and HPLC usually not the best way to initially characterise formulations. They both suffer from the problem that you only see what reaches the detector.

The normal way is to use TLC or simple column chromatography ( even SPE) along with solvent extractions. Once the extracts have been obtained, then GC or HPLC can be used, along with simple properties such as melting range, density, refractive index, solubility ( aniline point ), etc..

Many commercial waxes are complex mixtures of fossil and natural products, and most of those products unfortunately are complex chemical mixtures, which vary according to season and cultivar. You need to paint with a broad brush and use HPLC and GC to refine the selection.

Good luck,

Bruce Hamilton

Hey guys,

sorry i've been away for the weekend. As far as purchasing the recipie, that is pretty much out of the question because the guy making it is very tight-lipped about it. There is a pretty good possibility that there is molybedneum (sp?) in the lube and perhaps a bit of graphite but other than that, i'd say it's mostly made up of hydrocarbons from various waxes and other "greases". The lube is off-white in color as well. I highly doubt there is any teflon in the mixture however it is possible. This concoction has been around for probably 30 years or so and is unparalleled by any other lube commerically available. To be honest, nothing can hold a candle to this stuff. I don't know what it is about it but hopefully i'll find out soon.

Ralph, i'm going to mess around with the saponification of it soon and see if in fact it has tallow in it or see what else there may be. It seems like this is the right track.

Thanks again guys for all of your help!!! I will keep you posted with my progress!
Ruck