Blank Contamination

[rochelle]

We are analyzing TPH-G/BTEX(FID/PID) using Tekmar ALS 2016 (P/T)..and we always had a problem in our blank sample, we've got 30 ppb in toluene. Can you help us how we are going to eliminate the toluene in our blank sample? because when we experience that we always bake the ALS and GC, and sometimes it takes two to three days to eliminate the toluene contamination...Can you tell us the possible sources of this contamination? We have many samples for this analysis and we can't start if we have blank contamination ( Of course subtraction is not allowed .) Thanks... Pls reply...Godbless!

[Peter Apps]

Hi Rochelle

To be able to help we need a lot more detail about what you are doing. What is your sample matrix ?, are you ding direct desorption, or do you use an intemediate adsorbent, if so which one. How do you know that the contaminant is toluene - retention time only ? Do you have at least 30 ppb in all the samples as well. Do all the balnks have the same level of toluene ? etc etc etc

Peter

[AICMM]

Rochelle,

Some comments. One, what trap are you using and what are you desorbing/baking at? Two, do you get a toluene peak if you step past the purge on the 2016? You can do that from the keypad. If you start to purge and step right to desorb ready and let it desorb, do you still get toluene. Three, do you get toluene if you don't load a blank water? Look forward to your reply.

Best regards.

[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!