Blank Contamination part 2

[rochelle]

Hi Peter and AICMM,

Good Day! Here's my reply in your questions:

1. We are analyzing soil and water samples.
2. We are doing direct desorption
3. We know that it is toluene because when I look at the chromatogram I can see the toluene peak based also from the retention time. When we quantify the blank and the sample we've got 30ppb. And another thing, when we running our ccv, the theoretical concentration of the toluene is 30 ppb and now it is 60ppb. What we do to eliminate the toluene peak is we bake the Tekmar LCS 2000( sorry for the wrong info we bake the Tekmar LCS 2000
not the ALS 2016) at 290degrees and increase the oven temp to 200 degrees.
4.We are using J-trap, we desorb the sample for 2 min at 250degrees.
5.We haven't tried starting to PURGE then DESORB the sample. What we do is purge the sample for 11 minutes then DRY PURGE then desorb. But does it have aby interference in water? bec. we DRY PURGE so that the gas flows only to the trap to removed the water in the trap.

Thanks really. I've been doing GC analysis this for almost a year, and I do have many questions.. Hope that you can help me with that because I am really praying for it... Thanks and Godbless!

[AICMM]

Rochelle,

My first guess was that it was in your trap (especially if it was Tenax.) Now, not so sure since the J can typically take some pretty high temps. How old is your trap?

Think of your system in thirds. ALS 2016 vs LSC2000 vs. GC. Run a blank run of the GC (start button only, no desorb from the LSC2000.) Should eliminate the GC. Then, if clean, run a concentration cycle with no water to make sure you don't have toluene in your water. Next, run a concentrator cycle and step out of purge as soon as it starts. LSC 2000 should go to desorb by itself at that point. If you don't see toluene, look at contamination in your 2016. If you do see toluene, focus on your 2000.
I think you get the idea...

I'd be interested to hear what you find out...

Best regards.

[EnvironLab]

Just thought I'd mention that we've received batches of vials that were contaminated with toluene in the past.

[chromatographer1]

The J trap contains graphitized carbon. This does not contain toluene or decompose into toluene. Toluene must then be coming from somewhere else in your system. Check seals, solvents, vials, atmosphere in your lab etc. and try to find the source of the toluene.

The carbon will adsorb toluene from the air readily.

Tenax can decompose into toluene but your trap should not contain it.

Good luck !

Rod