Looking for a way to selectively detect toluene in an assay

[rycar88]

We are soon going to need to detect low levels of toluene in an assay we are performing. Toluene currently coelutes with the large peak of the compound we are assaying. This compound is nitrogenous based.

Some colleagues want to try a new column that will separate toluene from our compound, but we will have to change all of our methods and procedure along with that. I want to see if we can choose a detector that will selectively detect only toluene at that RT.

I have used PIDs in the past to detect aromatic VOCs against petroleum hydrocarbon samples (EPA 8021). I was hoping that would work here, but the ionization potential of nitrogenous compounds look like they are as low as or lower than aromatics, especially toluene.

Is there another detector we can use for toluene that ignores this other giant peak?

[BMU_VMW]

(triple quad) ms ?

[rycar88]

Yeah, triple quad MS might be the best option for this. It is maybe excessive for detecting this one compound but if it can serve as justification to get a MS that would be nice haha

[rb6banjo]

Are you using GCMS in the analysis of your compound? Toluene gives a fantastic m/z=91. If you sort your TIC by m/z=91, it's likely that everything else will disappear. I do this all of the time - sort TIC's by the mass of interest before I integrate the peaks. Works well. It's rather like using the detector as another "mode of separation" in your chromatography.

What is "your compound"? Does it have a significant m/z=91 in its mass spectrum?

The triple quad would be nice to have but there's likely a way around what you're trying to get.

[James_Ball]

Agree, unless the other compound has 91 in its spectra MS would be the way to go, even if just single quad. Triple may not have that much sensitivity for Toluene since the secondary ions are relatively low abundance.

[rycar88]

Thanks for the replies. This assay is for hydrazine, which doesn't even have a mass as large as 91 so I think that would work. (Looks like its primary m/z peak is 32)

I've never done assay work with MS before but in the past I do remember that they can dirty easily. Is there a risk running a direct injection assay of hydrazine onto a mass spec, either by damaging or dirtying it? Our assay method has a 1uL injection with a split ratio of 4:1.

[Simon Wicks]

Toluene is a pretty easy molecule to detect. You can use most detectors, though MSD is favoured as you get better LOD/LOQ and the selectivity is far better.

I'd suggest using something like a DB-624 or equivalent. The only thing that tends to co-elute with toluene using that column is nonane. That can be tweaked to separate. If you have access to a GCxGC FID, you can use that aswell. You get great separation by that technique. However, your LOD wont be great.