Chromatography Forum

As I head out for Easter weekend I will post this question.

Does anyone know of any contract labs that specialize SEC or GPC. We have a difficult task where we need to take a sample composed of white petrolatum, white wax, mineral oil, and paraffin; and figure out what are the relative quantities of these materials.

Of course, this is a very difficult analytical challenge and it has been suggested to me that it may require some kind of multidimensional size exclusion separation.

Does anyone know of any labs that might know how to approach something like this. Or that are pretty sharp when it comes to GPC/SEC techniques.

Much thanks and happy Easter.

You can try Polymer Standards Service. Here's a link to the web site: http://www.polymer.de/services/analytical-services/

The US guy is Michael Gray. The web site is http://www.pssgpcshop.com/service.htm.

I've never used PSS for this sort of work (I have my own lab), but they know their GPC/SEC.

Hi Adam,

I’m not a GC expert, but it’ll be one of my life’s greatest chocks if it turns out to be impossible to do the job by utilizing that great technique.
Try posting your question on the GC “sub – menu/departmentâ€

Hi Danko,

It's unlikely GC will be of much help for most of these separations.

These molecules have very little volatility so, even with direct on-column injection into a short thin-film column ( eg 5m x 0.1mm x0.1um ), only the most volatile and stable compounds will consistently come off. Some may degrade on the column - depending on what else is present.

You will see profile for each material, but they may be very similar - especially the white wax, white petrolatum and white paraffin ( depending whether their boiling ranges overlap, as each of these categories have products that range from liquids to high melting point solids ). If they are greatly different in composition and properties then GC may help, but so too would other techniques - such as DSC, FT-IR, etc.

The mineral oil may either a paraffin type or a lubricant base grade type - which may provide a unique GC profile. Unfortunately, the higher resolution required often inhibits the complete elution of higher boiling material.

My suggestion would be that a mixture of techniques may assist. Certainly GPC/SEC is worth a try, but I'd also suggest talking with the staff of a refinery laboratory that produce these products as to possible alternative techniques that look for unique markers/properties in each.

Hi Bruce,

It’s plain to see that you know more about GC than I. So, you’re probably right in your prediction.
Anyway, it was just an impulsive idea and in order to find out how far from the truth I was, I did a google search and found these 2 links (among several) that might support a potential GC application.

http://lipidbank.jp/cgi-bin/detail.cgi?id=WWA4101

and

http://www.sciencedirect.com/science?_o ... 72d2e2d5a5

Otherwise; respect! I know my place

Best Regards

They demonstrate why I doubt that the different paraffin wax forms will resolve sufficiently to be useful. If results do show major differences in carbon number profile, other properties will also be significantly different.

The first gives the typical n-paraffin profile, but using a special column. If you search Google for GC Simulated Distillation columns, there's a metal coated column ( from Restek? ) that will allow even a small amount of 100 carbon paraffin to pass through at 400C+ oven temperature.

However when you look at such profiles, even with a 400C+ injector temperature, and 350+ oven temperature, the typical "decreased volatility = decreased peak size", tail profile usually starts around C50.

It's pretty common in most high melting-point paraffin waxes ( regardless of type ) that the higher carbon tail following that volatility profile. That means that high melting waxes have the same tail profile - based on instrument conditions, rather than original sample.

The second example appeared to be a formulated lubricant which could have 20% of additives that generate profiles. Lubricant basegrades ( which obviously aren't paraffins - otherwise we would have solid engine oil at room temperature ) have a characteristic "two hump" peak profile.

The peaks represent different structural HC families. but also tend to become similar as higher MW fractions are compared.

One problem is that such high injector temperatures can modify profiles ( eg via thermal cracking ) and minor instrument condition changes can also create significantly-different profiles.

There's no reason why the original poster can't try analysing their samples using GC, and it may be helpful, depending on the specific samples, but I'd try other techniques first

Hi Bruce,

Thanks for comments. You obviously have a great knowledge of GC stuff.

Best Regards

As I head out for Easter weekend I will post this question.

Does anyone know of any contract labs that specialize SEC or GPC. We have a difficult task where we need to take a sample composed of white petrolatum, white wax, mineral oil, and paraffin; and figure out what are the relative quantities of these materials.

Of course, this is a very difficult analytical challenge and it has been suggested to me that it may require some kind of multidimensional size exclusion separation.

Does anyone know of any labs that might know how to approach something like this. Or that are pretty sharp when it comes to GPC/SEC techniques.

Much thanks and happy Easter.

Adam,

As others have suggested PSS is well equipped with 2D-LC or special GPC applications (GPC-FTIR, etc).

Besides 2D-LC you might want to consider LC-MS using APCI or APPI (at least for part of the sample).

Do you have already an idea of the molecular weight of your analytes?

For mineral oil (if the mw is low enough) GC-MS might be a way (depending on the complexity and on your matrix).

Good luck.

I believe we use American Polymer whenever we need a profile done. Not too expensive and fast turn around.

In the US, Jordi Labs might be able to help: http://www.jordilabs.com/

You might like to also consider MALDI-MS. The following compares SEC, SFC, and MALDI-MS of different waxes. They note that degradation is reported to start at 350C, so apparently did not pursue high resolution GC.

Characterization of technical waxes. Comparison of chromatographic techniques and matrix-assisted laser-desorption/ionization mass spectrometry
G. Kuhn, St. Weldner ,U. Just, G. Hohner
Journal of Chromatography A, 732 (1996) 111-117