Chromatography Forum

Hi all,
I am looking running analysis of limonene from recycled plastic pellets using HS-GC-MS.

Does anyone have experience of this? I am having trouble getting full recovery of the limonene in the first injection.

Any recommendations would be appreciated.

Please give more details on the goal of your analysis and how you are performing it.

If you are looking for quantitative (exhaustive) extraction of limonene from the plastic using headspace techniques, you're not going to have great success. If you are just trying to determine the amount of limonene in the plastic, headspace sampling will get it for you.

Hi,
I am currently trying to determine the level of limonene in the plastic for quality control purposes (must be under 20ppm).
Method is simply weighing 0.1g of pellet into a HS vial and using static headspace analysing the limonene. I am using standard addition for the calibration samples.

Issue is trying to extract all of the limonene from the pellet, after 2/3 injections of the same sample the limonene is still being detected at about 70% of the original injection.

We used encapsulated limonene in some consumer products decades ago. We pulverized the samples in methanol to extract the limonene.

I'm not surprised you don't see much change in the limonene concentration in the vapor space. The gas/solid partition coefficient is much in favor of the limonene staying in the plastic.

Your quantitative number is likely correct - if your analysis is well behaved and you've verified that the response is linear with changing concentration.

The only ways I know to exhaustively extract the limonene from the plastic is to 1) heat the sample and flow an inert gas in and out of the tube (collect the effluent if you want to trap the limonene) until it's gone OR 2) extract the plastic (serial extractions) with a solvent until you get it all out.

Could you consider extracting the limonene using a solvent as mentioned above, cleanup/concentrating the sample, and using a liquid injection instead of headspace?

Hi guys,

I have set up a series of solvent extractions to see which has the best extraction efficiency and will continue method development from there.

thanks for all the help and recommendations!

Do you really need to get it all out or do you merely have to know how much is there? In your original post, it's not clear. On the one hand, you mention that you need to know how much limonene is in the plastic but on the other hand you mention that you're alarmed that subsequent injections of the same sample shows a lot of limonene in the vapor.

Static headspace relies on an equilibrium (dictated by the partition coefficient, a thermodynamic parameter that is constant for a given set of sampling conditions):

Kd = Cg/Cs

of the analyte between the condensed phase and the vapor phase. Cg = conc analyte in the vapor phase, Cs = conc analyte in the condensed phase. It doesn't mean that all of the material leaves the condensed phase and moves into the vapor phase.

You don't need to have it all out of there to know how much is in there.

Hi,
for quality control purposes i just need to know that the amount of limonene is below 20ppm in the plastic pellets.

The exhaustive extraction is a waste of time - provided the headspace method is a good one.

Limonene should be easy. It is very stable, not very high boiling, inert should not have issues on even the most poorly deactivated system. Just crank the temperature to maximum 150deg C or whatever. Or dissolve it in acteone and do FET. Acetone melts many plastics and has a low boiling point so it should not interfere with limonene.

Excellent!

Thanks again for your help guys!