I am currently attempting to discover a clean-up method that would work to strip hazardous waste fuel samples of Freon, while preserving any PCB Aroclors that might be present. We use Varian 3400 & 3800 GC's with ECD. The fuel has up to 32000 PPM Freon, and our burn limit on the PCB's is only 50 PPM. The Freon is totally obscuring elution points of the 1016, 1232, and 1242 Aroclors. Any assistance would be appreciated.

Is it possible to evaporate the FREON adding a solvent such as isooctane to keep the PCBs? In my experience FREON is much much more volatile than PCBs. Maybe I am missing something in your method.

I am a little puzzled by the statement that the Freon is interfering with the PCB peaks. As noted in the above posting, Freons are much more volatile than the PCBs, and I would expect that the Freon would be long gone before the PCBs eluted. Try the suggestion above, and I would take a measured volume of sample and evaporate to near dryness, then redissolve in a hydrocarbon solvent.

try sulphuric acid cleanup on your samples (.5ml acid in 1mL sample and shake), acid mays help to get rid of the interferents. If sulphuric acid cleanup does not work, try florisil (spe) clean up on the extract. good luck

Our current cleanup is as follows:
0.1 to 0.15g of sample is placed in 5ml Hexane & mixed. Then 1ml of this is added to 5 ml of Hexane spiked with 0.005ul/ml of DCB (internal std). 1gm of florisil is added and shaken. Hexane is poured off into a vial with 2ml of Sulfuric Acid and "a pinch" of copper & shaken. This is centrifuged and the Hexane is drawn off into another vial & mixed with 1gm of florisil & shaken. 1ml of this is transferred to a vial and boiled off, then reconstituted with 1ml of Hexane and shot. That gives us a 200:1 dilution.

The concentration of Freon in this sample is approx. 32000 PPM. Our upper limit on PCB's is 50 ppm. It is possible that the Freon is saturating the column. Regardless, the congeners are not visible through this interference, and we have no alternative but to reject the load, since we cannot tell whether the PCB's are present or not.

How do you know the interference is Freon? I you are evaporating the samples to dryness, then redissolving, I have trouble believing that there is that much Freon left. Also, Freon should have distinct peaks, and it is hard to believe that the residual Freon left after evaporation to dryness would obscure 3 Arochlors.

My guess would be that you are seeing either the "hump" from hydrocarbons or sulfur containing compounds in the fuel interfering with the PCB analysis. Remember, ECDs will respond to any compound present in high enough concentration, not just halogenated compounds.

A mass spectrometer run to identify the identity of the interference or at least the chemical class would go a long way towards providing information to help solve the problem.

I have to agree with Anon. above. The interference you are seeing is probably sulfur. In my experience copper is slow to clean up sulfur. I would try doing the copper cleanup seperately from the sulfuric acid cleanup and letting the sample sit in contact with the copper overnight, or even longer. Also, try using more copper.
Another suggestion would be to change your oven program. I would think a low enough starting temp. could be found to resolve freon from the early Aroclor peaks. Also, you could try the process with a "blank" matrix to ensure that you aren't introducing the interferent along the line.

Hi Dennis,

The addition 1gram of florisil in the sulfuric acid cleanup did not do any good to your extract. All you are doing there is reinducing hydrocarbons into the sample. From experience, Sepak (Florisil cartrige from Waters Corporation-1grm size) should be able to separate hydrocarbons from Arochlors. My recommendation for the procedure as follows;

-take 1mL of your sample and performed sulfuric acid cleanup, dilute the sample if necessary.
-transfer 1ml of the extract into a preconditioned Sepak (SPE)column. Elute the column with 5mL hexane and collect the eluant. Perform the neccessary blow down to get rid of freon or take 1mL of the sample and run on your GC/ecd. Hydrocarbons (humps-cutting oil,Halolube, grease may cause interferent) should be retained in the florisil column. If you are not seeing arochlors, the sample size may be too small. Perform blank and spikes to ensure the proper separations.

good luck