PCB in Transformer Oil using ASTM D4059

Discussions about GC and other "gas phase" separation techniques.

5 posts Page 1 of 1
We are in the process of replacing our Agilent 5890 with an Agilent 7890. This GC is used exclusively for analyzing PCBs in transformer oil, water, soils and wipes. We set up the 7890 with the same packed column that we used in the 5890 and the same temperature settings. The only difference is the 7890 has a micro-ecd while the 5890 has an older ecd (non-micro).

Here's the problem, whenever we run a new pcb-free transformer oil on the 7890 we get several peaks that appear in the first 5 minutes of the run. These peaks are significant and reproducible, no matter what transformer oil we run. These peaks do not appear on the 5890 for the same oils. Also, none of these peaks appear when we anlayze a hexane blank or when we analyze pure mineral oil.

For sample prep we dilute 0.4 grams of oil with 19.6 mL of hexane and treat every sample with fluorisil and have even tried acid treating the pcb free oils.

Do we need to change our sample prep procedure or do we need to install a cleanup column? Help please.

Do they appear in blank injections of pure solvents, or blank injection of a clean transformer oil extract solvent?. I'd focus on any switching valves in the sampling sequence.

I would also check that you are not seeing dissolved gases by ultrasonicating or vacuum degassing the solvent extracts. I assume you have tried a different supplier of hexane - and are using a pesticide residue analysis grade, which has low ECD response.

A more remote possibility is that the Molesieve purifiers in your carrier gas lines are contaminated, especially if new lines were installed for the instrument, there could be traces of halogenated cleaning solvent from new lines.

You have to be systematic, and define what has changed, and also ask Agilent to contact others who are using the instrument for the same method to get any hints. You should not have to cahnge your procedure.

Please keep having fun,

Bruce Hamilton

Do they appear in blank injections of pure solvents, or blank injection of a clean transformer oil extract solvent?. I'd focus on any switching valves in the sampling sequence.

I would also check that you are not seeing dissolved gases by ultrasonicating or vacuum degassing the solvent extracts. I assume you have tried a different supplier of hexane - and are using a pesticide residue analysis grade, which has low ECD response.

A more remote possibility is that the Molesieve purifiers in your carrier gas lines are contaminated, especially if new lines were installed for the instrument, there could be traces of halogenated cleaning solvent from new lines.

You have to be systematic, and define what has changed, and also ask Agilent to contact others who are using the instrument for the same method to get any hints. You should not have to cahnge your procedure.

Please keep having fun,

Bruce Hamilton

We do not see these peaks when we inject blank solutions of pure solvent (hexane), only when we inject a pcb free transformer oil that has been dissolved in hexane.

I've considered changing the traps on the carrier gas, but since the only time we see these peaks is when we analyze transformer oil, I'm assuming that these peaks are due to something in the oil. Something that is being detected by the micro ECD which is supposed to be more sensitive than the old ECD on the 5890.

I've already contacted Agilent and asked them to query other users to see if they are seeing the same peaks, but have not heard back from them.

OK - thanks for that.. sorry for the duplicate post, not sure how I did that...

Does the peak size change with the transformer oil dilution, keeping the injection volume the same?. Also, if you change the oil dilution and the injection volume ( halve the concentration, double the injection volume ), do the peak shapes and areas stay the same? Are the peak shape very sharp, or tailing?.

Given that you see the peaks only when transformer oil is present, does their size/shape matter whether it's used or unused transformer oil?. I assume you've looked for correlations of the peak size with the oil, and haven't found any...

I assume you have treated the solvent and pure mineral oil exactly the same as the used oil samples, ie , same containers, diluent dispenser, Florisil treatment, injection system, etc. - that's what I meant by a "blank injection".

I would definitely keep on Agilent's case, because if it's related to samples, other users should also have seen the early peaks when they switched to the more sensitive detector..

Please keep having fun,
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