Using an Internal Standard

[july]

Where can I find information on using an internal standard?

We are introducing air samples containing VOC contaminants to the GC/MS to analyze the VOC concentrations. Samples are prepared in a 1L glass, gas sampling tube. Samples are withdrawn with a syringe and injected directly.

Someone suggested we use deuterated toluene for our internal standard, but I know nothing.

If we have a gas standard, should this be made in the gas standard cylinder that we purchase or is it normally purchased in it's own cylinder and added to each sample?

I saw that Supelco sells a syringe that allows you to add the internal standard directly to the sample in the syringe...but I'm sure there are other ways of doing this? I am curious to learn. Any information is greatly appreciated.

Thanks for your time.

[jimmyhu]

Toluene-d8 is a good option if a group of aromatic hydrocarbons is in your VOCs. Also 1,2-Dichloroethane-d4 is good for chlorinated hydrocarbons. For aliphatic hydrocarbons, nonane-d20 may be used.

Jimmy

[Peter Apps]

From your other posts you are working with simple mixtures spiked into clean air. So for an internal standard you can use pretty well anything that you have not spiked into the sample already and save the costs of isotope labelled materials. The problem with internal standards in MS is that the response factors will be different for every analyte and the i.s., but, again from your other posts, this will be the least of your problems.

Peter