Waxy sample injection

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OnurM
OnurM's picture
Waxy sample injection

Hi All,
I am trying to run several samples of very heavy petroleum which are waxy on GC. However due to waxy nature of the samples I cannot dissolve them in a solvent such as CS2 or DCM, and they don't get liquid at ambient temperature. Only way I could think of was to place them in a water bath. However it did not work either since as soon as I pull them away from the hot water bath samples got extremely viscous (even solid). Is there anyone who can help me out about this manual injection of those waxy samples problem?
Thanks in advance.

Venugopal Narne
Venugopal Narne's picture
Hi,

Hi,
you are not mentioned the sample quantity and boiling points of the Samples
If the sample quantities are low and boiling points also low you can go with inslating heating tapes
which can maintain a particular temperature for the sampler ((injection) and the sample cannot solidify
Please find sample insulating tape
 

OnurM
OnurM's picture
Thanks for your suggestion

Thanks for your suggestion however my sample size is as small as 0.5ul therefore I am using very small size syringe (5.0ul). I don't think such a heating tape would work on the kind of syringe.
In addition to information above my samples are extremely heavy (they look yellowish color and solid at ambient temperature and according to intial analysis that I could achieved to only analyze once; carbon numbers are as high as n-C60 to n-C70).
Thanks anyways for your suggestion. Any other idea??

Greg Pronger
Greg Pronger's picture
For your injection, what

For your injection, what concentration are you attempting to prepare (how much wax sample into how much solvent)?
 
I was surprised that methylene chloride and carbon disulfide didn't dissolve the wax; for that type of material they tend to be very good solvents. When you attempted these two solvents, did you try sonication to assist getting the material into solution. I've seen instances where the challenge is the initial dissolution of the material, but once done, the material would then stay in solution.
 
Greg P.

Dr. Analytical
Dr. Analytical's picture
What about the simple

What about the simple hydrocarbon solvents like pentane, hexane, heptane?  If this is a waxy material, with high MW components only , then you won't have to worry about interference from the solvent peak.
But I would be more concerned about your possibility of success.  If you really have C60 hydrocarbons, I'm not sure they will easily go through a GC.  A high temperature column will probably be required.  Perhaps Greg has some more experience along these lines, but as a general rule it is difficult to do GC on something with a MW over about 500.
SFC would probably be a much better choice.
 

OnurM
OnurM's picture
Thanks guys for the

Thanks guys for the suggestions, on the other hand, I have already tried all those things before hand. I am already using a High Temperature GC with a column which is capable of temperature raising up to 450oC. CS2 is my regular solvent already to dilute my samples. However for this instance I have tired all types of solvent that may help. I even mix some to get a result. But I haven't tried sonication, I will consider this.
And Greg, thanks again for the suggestions, the concentration I am using is usully 1/2 (w/v) however I tried several degrees up of this ratio such as 1/10 and I actually succeded. But the solvent peak was extremely high and sample peaks were almost invisible. But I will definetly try sonication.

Greg Pronger
Greg Pronger's picture
If you would, pass along your

If you would, pass along your instrument, type of inlet, detector,.column, instrument conditions, (inlet temperature, temperature program, detector temperature), injection volume including whether you're using an integrator or a data system and anything else you may consider important. With what you described, the 1/10 should give you very nice chromatography, and if you're using CS2, you should have almost no solvent peak (assuming this is on an FID). In any case, as heavy as your sample is we should be able to separate it completely from any solvent, and whether we simply have an integrator change attenuation, or some other integration parameter, we should be able to get you what you need.
Greg