Chromatography Forum

When I analyse siloxanes such as Octamethylcyclotetrasiloxane, Decamethyltetrasiloxane, Decamethylcyclopentasiloxane and Dodecamethylcyclohexasiloxane in air trapped on charcoal tubes, I use CS2 as desorbing solution and analyse the desorbant using GC-FID. When I analysed this desorbant using GC-MS for confirmation, I found an extra peak after that of Dodecamethylcyclohexasiloxane on MS chromatogram. There is no such peak on GC chromatogram. Mass library search with the quality of 94 shows that the peak is cyclic octaatomic sulphur [10544-50-0].

The first question is that sulphur can be detected by FID? Sulphur powder is easily dissolved in CS2 and my experiment in lab demonstrates FID can’t.

The second question is where sulphur is from? From the sample or as a result of the reaction (CS2 + SILOXANES) in GCMS system?

Jimmy

Hi Jimmy

An FID probbaly can see sulphur, but with such a low sensitivity that it effectively undetectable.

The sulphur is probably an impurity in the CS2, but it just might be coming from the air samples. Try injecting some CS2 on the GC-MS.

Peter