SCD Response

We use gas std of 18 compounds from C1 Mercaptan to C7 mercaptan, CS2, H2S, Dimethyl Sulfide, diethyl sulfide (10 ppm each). Does SCD provide same response for all the compounds? Disulfides give double response? Is it required to heat the std before injecting?

I read in some article that if disulfides are present in the std, it will deteriorate the std. In that case is it preferred to have 2 different stds having monosulfur compounds in one std and disulfides in another std?

Kindly advise

  • The SCD response is equimolar, so the response factors should be approximately equal when concentrations are noted on a molar basis.  The response factor of a disulfide will be double because two sulfur atoms are present on the molecule.  With the sulfur concentrations only 10 ppm each, I don't think heating the standard would be required.  Look at the response factors of the early eluting components compared to the later eluting components.  If there is a drop in response on the later eluting components, heating the standard may be necessary.

    I have not heard about the disulfides causing deterioration of the standard.  However, the sulfur compounds are quite reactive, with the mercaptans reacting more than components with alkyl groups bonded to the sulfur atom, such as dimethyl sulfide or diethyl sulfide.  I've seen standards that had only H2S, COS, C1 and C2 mercaptan start to show disulfide peaks (dimethyl disulfide, diethyl disulfide, ethyl methyl disulfide) from the mercaptans reacting with each other.  

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