Chromatography Forum

Dear friends,
I am working on Varian 450 GC having Galaxy software with PFPD (Pulsed flame photometric detector).
I am working on sulfur mode and i am trying to analyze Ethyl mercaptane in the LPG ( normally it is added in LPG near about 20 ppm).
I am collecting the LPG from cylinder to a 2 Ltr. taddler bag and analysing it through sample loop.
I am getting four peaks of sulfur ( after Ethyl mercaptan retention time i am getting three more peaks)
When i am injecting blank of helium from the same poly bag i am not getting sulfur peaks.
I just need help to understand why i am getting the four peaks of sulfur in LPG.

There are a large number of sulfur compounds after ethyl mercaptan. Any number of possibilities. The list is narrower in front but after....

I assume (risky business that) that they are smaller than the ethyl?

Best regards,

AICMM

These are likely disulfides and possibly one sulfide. Purchase DMS, DMDS, EMDS, and DEDS; spike them in a tedlar bag filled with nitrogen (or helium) and match up the retention times of this "standard" with the sample.

I am not clear about these impurities. These are generated with time in poly bag or they are present in the Ethyl mercaptan and when we add in LPG cylinder they are accumulating with time or they are generated with reaction by LPG

My feeling is that your impurities are already present in the ethyl mercaptan (added to the LPG to enable detection of a leak by odour )

Can you obtain and run a sample of the ethyl mercaptan used diluted in something like nitrogen to confirm?

Do you have a control of LPG only without addition of ethyl mercaptan to check?

Can you post a chromatogram showing the impurities relative to the ethyl mercaptan?

Unless already present in the LPG it is extremely unlikely that LPG itself will interact to form impurities

It is not clear about these qualities and purity. These are generate with point in poly bag or they are present in the Ethyl mercaptan and when we add in LPG cylinder they are gather with time or they are generate with response by LPG. Like Custom Essays provide full guarantee of quality work and time duration also no compromising for customer

I believe that those suggesting the presence of disulfides are correct. A mixture of ethyl mercaptan will ultimately produce some diethyl disulfide and even lesser amounts of tri, tetra sulfides...

Throw in methyl mercaptan and you can form methyl ethyl disulfide, giving at least 5 sulfur compounds from those 2. It helps to avoid the presence of oxygen.

In any case, I wanted to say that it's generally best to sample the LPG as a liquid, either into a liquid sample valve or through a vaporizer in order to minimize headspace effects.

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Hi,
I am the analytical chemist for SCION Instruments (formerly Varian). Please visit our application website where you will find a specialised application note on sulfurs in LPG, using Varian/Scion GC and software. If you need any more information please feel free to contact me on ashleighm@scioninstruments.com

https://scioninstruments.com/resources/