What to use as internal standards

[Roxanne42]

All right, I'm aware this must have been discussed before but I couldn't find anything relevant through the search function within the first 200 hits.

I'm not an analytical chemist and basically, I'm wondering what sort of compounds to use as internal standards in GC analysis... Some people here have been using tetralin, chlorobenzene or 1,4-dioxane...

What are common compounds you use as internal standards? I'm looking for examples of standards you use in organic medium, and some that you use in aqueous mediums...

Thanks,

Roxanne.

[zokitano]

It depends. For which analytes are you planning to find suitable internal standards?

[Ron]

As a general rule, you want something similar in chemical properies to the analytes of interest. For example, in nlood alcohol analysis n-propanol is used as an internal standard for ethanol. n-Propanol is similar in polarity and boiling point, and does not naturally occur in the samples. In many cases an isotopically labeled compound is used as the internal standard.

[Consumer Products Guy]

As a general rule, you want something similar in chemical properies to the analytes of interest. For example, in blood alcohol analysis n-propanol is used as an internal standard for ethanol. n-Propanol is similar in polarity and boiling point, and does not naturally occur in the samples. In many cases an isotopically labeled compound is used as the internal standard.

Yes, n-propyl alcohol is an excellent internal standard for ethanol assays, even detailed in AOAC. So of course USP611 utilizes acetonitrile, completely different polarity, in its ethanol assay.

We've used butanediol as internal standard for glycerin and propylene glycol. Like poster stated: best is similar solubility, size, polarity to analyte of interest, but NOT present in your matrix.

[Roxanne42]

Thanks for the replies.

It's hard to say what since I manage a high-throughput lab and I have many different people coming in with different types of chemistry. This particular student is doing reactions with ethyl-4-chloro-3-hydroxybutyrate (http://www.chemblink.com/products/90866-33-4.htm) in water.

Another ongoing project concerns the formation and quantitation of hydrazones in organic solvents.


Again, thank you for the input.

[karthic]

Yes, Propanol is a good internal standard for ethanol but since my fermentation microbes produced propanol I had to use methanol.

Another criteria of selection could be to make sure it elutes close to your compound of interest (Which will occur if they have similar chemical properties).

Karthic

[shan820]

If you can't find the appropriate internal standards in a literature search of published papers for you analytes of interest, I would consider calling tech support at some standard manufacturers like Restek and Accustandard, or Cambridge Isotopes (if you are doing mass spec) and get their advice.