Chromatography Forum

Hi all,

I'm trying to analyze pcymene in wastewater. The current EPA method recommends a purge and trap, but I don't have this technology available. Instead, I was hoping to extract the organic out of the wastewater and analyze via GC, however, I'm not having any luck. There are many other organics in the wastewater and when I attempt to extract with methylene chloride, it appears that an emulsion is created (I only get back about 2-3 mL of solvent for every 10mL, using 100 mL sample.)

Shooting the wastewater sample on the GC doesn't give accurate results, presumably because I can't get a uniform sample due to solubility issues.

Any thoughts?

Thanks in advance.

Since p-cymene is very hydrophobic and water has a low solubility for it I am not surprised at your results. The other hydrocarbons present probably allow a minimal solubility for the p-cymene.

I would suggest you perform multiple (3-5) 10mL extractions of the water sample, saturating the water with hydrocarbons, using perhaps pentane or hexane.

Combine the extracts and CAREFULLY distill the lower hydrocarbons off leaving behind the p-Cymene in a measured volume (2mL?).

I have performed a similar analysis for C6-C20 hydrocarbons in a soap-like matrix and was successful in measuring less than 5ppm.

You can spike the pentane extraction with p-cymene to do recovery studies.

Good luck,

Rodney George

CMES:

Given that your query analyte has methylated/alkyl side-chains bound to an aromatic ring, suggest that you conduct the extraction using Toluene as the extraction solvent, a suitable internal standard e.g., o-cymene, and employ a centrifugation to ameliorate the flocculent middle layer, and finally evaporate to concentrate the, thus:

To 5 mL gross sample, add 1 milligram of int.std., add 5 mL Toluene, shake 10', then centrifuge at 2000rpm for 5', remove supernate, then repeat this process at least twice. Pool the two extracts and evaporate them down to ~ 2 mL in a KudernaDanish flask (or suitable evaporative liquid measuring device). Dilute this extract by 1:10 with Tol.

Inject onto your GC.
Use a non polar column e.g., HP-5, and ramp the temp slowly to determine the elution time/temp for your assay.

Pls report back to us--progress or no?

Chromatographer and Jumpshooter-

Thank you both for the quick replies! We will attempt both methods in the lab tomorrow, and I will post back as soon as we have some results. We currently use toluene for other extractions in the lab and think that will be a good solvent choice if results are positive.

Thanks again,
Christy

Don't be surprised at the amount of water the toluene may carry over. Plus the toluene may have contaminants in the range of p-cymene that may make any measurements difficult after they are concentrated by the evaporation process.

Good luck,

Rodney George

Another trial might use headspace of a 2-5mL volume of the aqueous matrix and use high resolution or multidimensional chromatography to resolve the p-cymene from the other hydrocarbons. Of course, this would be dependent upon the amount and type of interfering hydrocarbons present.

best wishes,

Rodney George

You say that 2-3 ml of methylene chloride can be isolated. If you correct for an internal standard (deuterated cymene) and inject on a GC/MS it might be OK?

cms12,

Have you tried salting out, freezing out, and spinning out your samples? It is still possible to get most of your solvent back from tough matrices with patience. Otherwise, you might look at micro-KD's from someone like Supelco and go down the path of multiple extractions as noted by Rodney.

Best regards.