Residual solvents analysis (acetonitrile, ethanol & DMSO)

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

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I'm currently working on my MSc project for residual solvents analysis using GC-FID. As the compound of my interest uses acetonitrile (ACN), ethanol (ETH) and DMSO during the synthesis and labeling, I would need to know the level of impurities.

I have a GC-FID (Shimadzu GC-2010 series) in my lab. I have prepared the solution of 0.1M conc for each (ACN, ETH, DMSO) and proceed to the mixture of solution in accordance with the ratio 1:1:1. The details of chromatography condition are as follows:
Injection: splitless
Sample holding time: 30 sec
Injection port temp: 240 deg C
Column/oven temp: 50 deg C hold for 1 min, then 10 degr C/min to 200 deg C
FDI temp: 250 deg C

air flow : 30
FID gas flow: 40
make up gas flow: 400

I have injected the mixture and able to separate it into 3 peaks; Rt ETH: 3.0 min, Rt ACN: 3.9 min & Rt DMSO: 10.95 min.

I validated it using a single injection for each. The Rt for ETH and ACN were consistent. Interestingly, the Rt for DMSO has shifted and appeared early at about 3.1 min.

I injected the mixture again to observe whether I could get the same separation as the first one. Surprisingly, no peaks appeared. I'm not sure whether this was due to any instrumentation error but the system did not give any error. Kindly advise.

What column and dimensions are you using? Regardless, by my calculation your standards are around 1500 - 2600 ug/mL which is a lot for a splitless injection. I would try running with a split of 1:10. Your retention times for your first mixture injection seem about right; Rt ETH: 3.0 min, Rt ACN: 3.9 min & Rt DMSO: 10.95 min. Not sure what happened after that. Try running again with the split and see what happens.

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