Chromatography Forum

I am trying to develop a method for 1,4-Dioxane. I am using a 5975 and 7890 GC/MS with a PTV inlet. I was successful at splitting the methylene chloride solvent from dioxane but dioxane is splitting into about six peaks. Our volatiles analysts see this same problem when they analyze using purge and trap. Any thoughts as to why this happens? All literature I've read shows nice neat sharp peaks for dioxane.

Column: Rtx-5Sil MS 30m/0.25mmID/0.25um with 10m integra guard

EDIT: I tried running hot splitless and do see a single peak for dioxane. When I run cryo using solvent vent mode it comes out as a blob just after solvent peak. Hopefully I can come up with the right parameters...

How about your analysis split ratio? The peak splitting problem is seem to be came from some kind of reasons: focusing method; column flow-rate; GC oven temperature program and the last is split ratio. In my case, 1,4-Dioxane could be analyzed well under this condition: cryo-trap focusing(-30deg); inlet split ratio 20:1;column flow 1ml/min; from 40deg to 300deg of programmed oven temperature. Acctually, I didn't develop individual method for 1,4-Dioxane, and this one sometimes was found in some kind of our environmental samples.

Are the various dioxane peaks confirmed by MS as dioxane, or are they something else? I'm wondering if it's degrading/reacting

I think there is no way to degrade or react with something, if it happened, 1,4-Dioxane or anything interested target couldn't be found by MS Library Searching work, because the degrading and reaction always form another compound with higher or lower Molecular Mass or different itself structure.

I don't believe dioxane is reacting or converting, but it's possible. All spectra look nearly identical. If I vary the conditions I can get a single peak, but it is so close to methylene chloride that some could be coming out on top of the solvent. I am limited right now with my inlet, I have a PTV with CO2 cryo using a multibaffled liner which has an internal volume of 150uL. I'm using an RTX-5Sil MS 30m, 0.25mmID, 0.25um. I hope I can get away with using this column and not have to buy a column with a thicker coating, as I'm using this column for other analyses as well. It would be nice to not have to change the column in and out with another. Also I am right at the beginning of developing this method so what I'm trying right now may be totally inappropriate. Curious if -30C would work for inlet temp? Seems way to low to vent methylene chloride away but I can give it a shot. More to come... Thanks...

Ok I think I have come up with a usable method where dioxane does not split! It was suggested by a coworker that perhaps I was injecting it too concentrated and that is why it was splitting. Could be....I was testing at 20ppm now I'm testing 0.1ppm and it seems to be working ok. It continues...

I am still having issues with this. 1,4-Dioxane is wandering in retention times, splits for some runs but not others, total response wanders as well. I think I have to tweak the inlet/cryo conditions in some way. Just don't know how yet.