-
- Posts: 24
- Joined: Fri Apr 30, 2021 1:10 pm
- Location: Italy
I have been using this tecnique for many years, but now I have recently introduced the internal standard for VOC analysis in air with ISO 16000-6. The method require the use of tolueneD8 internal standard.
I can use both VOC standards and TolueneD8 standard only as liquid solution, because I do not have the possibility to introduce them gaseous directly in the thermal desorber. Liquid addition of these standards is allowed by ISO 16000-6 but it is not specified if I have to add Internal standard solution to the tubes for samples, before air sampling of after air sampling.
Actually, I add internal standard solution after air sampling and then I put the tube in the desorber and I performe GCMS analysis. In the last months I saw that in some samples the peak of IS falls down. The Area decreases about 5-10-20 times respect to the Area of IS in the standard samples. Surely there is some trouble with sampling, but it is not my fault because sampling is performed by external people different from my company. We just perfom analysis.
I am asking you, If you have the same problem and when do you add internal standard solution to the tube. Do you add it before or after sampling?
NB: I add liquid standards to the tubes by using a Supelco flowmetere with inert gas. I always add 1uL of methanolic solution of multistandard as request by the standard ISO 16000.
Thank you very much.
Please write my also If you need suggestions for TD-GCMS.