DMA or NMP as diluent for HS-GC

Discussions about GC and other "gas phase" separation techniques.

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Hi all,

In our pharma lab, we need to select the best sample diluent for some HS-GC methods. We have a lot of residual solvents to control.

Could you please give your feedback about the pros and cons of using DMA or NMP? Specially considering:

- availability and cost of pure HS grades
- possible residual impurities (e.g. DMF in DMA) or stabilizers
- "cleanliness" of baseline (e.g. critical interfering peaks)
- solubilizing power for apolar and polar substances
- boiling point and its impact on HS-GC performance (implications on HS oven temperature)
- impact on the extraction of multiple residual solvents
- any other relevant parameter

We have initially rejected DMSO and DMI due to the common degradation/purity/high cost issues.

Thanks in advance
I have used the headspace-tested grade DMA previously (Sigma-Aldrich) and found it perfectly acceptable for routine residual solvent use. However if I recall correctly, I was only analysing for 2 or 3 residual solvents of fairly low polarity, so it's hard to say how it would fit your method.

Regarding the DMF impurity in DMA, I don't think DMF is very amenable to headspace analysis so even if it is in there, it's unlikely you'd transfer it to your column, unless you have a very high equilibration temperature and high agitation in your headspace sampler.
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