ghost peak gc-ecd organopesticide analysis

[krickos]

yes, we use all solvents from a plastic squeeze bottle but it only seems to affect my machine, there are older 5890 gc's so maybe they are not as sensitive

well, might be related in some part, depends which ECD the 5890s are hooked up with (older?) compared to your 6890 (guessing newer µECD?!)

[Peter Apps]

yes, we use all solvents from a plastic squeeze bottle but it only seems to affect my machine, there are older 5890 gc's so maybe they are not as sensitive

So you take clean methanol from the glass bottle that it comes in, and put it into a plastic bottle that leaches contaminants into it and has crud accumulated from how many cycles of filling and long=term exposure to dirty lab air ? Bad idea.

Peter

[dalarie]

I have tried using new solvents directly from the glass bottle, run overnight and still the same result so I don't think it is the solvents

[Peter Apps]

I have tried using new solvents directly from the glass bottle, run overnight and still the same result so I don't think it is the solvents

What grade of solvents are you using ? Anything other than pesticide grade is risky - the ECD's sensitivity is great for finding analytes, but a curse for picking up contaminants that are invisble to other detectors.

Peter

[Ryklys]

I have tried using new solvents directly from the glass bottle, run overnight and still the same result so I don't think it is the solvents

Funny question, but... Have You tried to concentre 100-200 ml to 1-2 ml of the solvent? Cos I noticed, that even bad grade solvent show no or next to no contamination when analysed ''raw'', but when you concentrate (and that usually happens during sample preparation) the same solvent, you get very different result.

[dalarie]

No I haven't tried that but I don't believe it is the solvent now. I ran 10 injections with no syringe and the peak was still there, did not decrease.

Here is where it gets fun. I received a brand new HP7890 GC dual ECD. I started running it today and bam contamination peak. Now, I am using hydrogen instead of helium for the carrier gas, 2 totally different column from Restek. The only thing that is the same is the make up gas which is nitrogen. I really cannot figure this out.


Another thing, I performed maintenence on my other instrument today and used Dichloromethane as the cleaning solvent instead of methanol. I rinsed the inlet and scrubbed the entry to where the carrier gas line goes. The peak almost completely disappeared even using the same solvents?? What gives? I used dichloromethane on the last maintenence (did not rinse the inlet) and the peak was there.

[Peter Apps]

Using a chlorinated solvent to clean a system with a detector that is selective for halogenated compounds might not the best idea.

Peter