I am carrying out reaction with Organophosphorus compound which when dissolved in methanol shows peak at 5.77. But when the compound is passed in vapour state mixed with zero grade air and again passed through methanol, the retention time is lowered to 4.11. What might be the reason for this?
Old column (previously used for other methods)
Method not validated (not robust)
Poor GC maintenance (leaks+)
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Are both being injected on the column in methanol diluent? What is the stationary phase of the column?
Yes the diluent is methanol. RT of methanol is around 2.4. its is standardised procedure. Coloumn is new only. No problem with it. Actually when I am making stock solution and injecting it, the RT is arnd 5.77. But when same stock solution is bubbled and the vapours generated are carried with zero grade air as diluent and passed in collection point where it is collection in methanol only. When that is injected in GC the peak is shifting towards lower RT of 4.11.
Typically that significant of a retention time shift wouldn't be due to column to column variations. It could be due to one of three things: A change in matrix causing a retention shift (but since you said everything is in methanol that shouldn't be the case), a change in some instrument condition, such as flow rate (but since this is a standard procedure that shouldn't be the case either), or somehow the compound is being transformed to something else during collection (or the compound is being lost and you are seeing something else. Point three could be verified by mass spec; not sure if this is an MS based method. This seems like a relatively complex procedure so I can't really suggest anything else with the limited information provided.
Thank you sir for the information. Yes I think due to some reaction only there is peak shift. I will try to work with MS for this. Thank you all:)
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