Things you can learn by running “nothing”….
Ran a head space blank (room air) today. It looked almost the same as yesterday’s (minus the methanol I was playing with yesterday).
Yesterday is in red, today in black.
So I went outside for some “fresh” air.
Lo the hydrocarbon peaks went away….
What is the take home message?!?
How many things can be gleaned?
Cancer
Sure: we be huffing solvent. All day, every day.
I only huff solvents M-F. The weekends I work at the gas station and huff gas and diesel fumes.
I’m wondering why your peak expanded from the nm range width outside
?!?
GC FID. Measuring mV
go take a sample in the bathroom… Give me 10 minutes though, I need to drop a sample off in the porcelain “vial.”
This is great, I gotta see if my headspace sampler works properly and give this a go. I think I’m fighting electrical noise from any one of the hydrogen, nitrogen, or zero air generators running alongside the GC. NFI what the peaks may be otherwise on this blank run.
This is the reality of life. As a chemist I was surrounded by all sorts of carcinogens/mutagens/explosive goodies.
Take your safety seriously. Wear PPE and make sure that respirators (if applicable) are properly fitted.
Above all else, pay attention to your lab HVAC in general to assure air quality. OSHA approves this statement.
Id call those peaks column bleed, basically little bits of your column stationary phase blowing out the end as the oven heats up, which is normal. Probably roughly follows your oven ramp temps. If your holding at one temp (like maybe just above room temp) and your still seeing random peaks, that’d be EM interference.
Totally a possibility. I did run the column through the ramps where the peaks come out settling on a bake out at 350c but little to no bleeding occurs AFTER temp is reached leading me to suspect the detector could be picking up interference from the heating element cycling on and off. I purchased a power conditioner to isolate the gc from the everything else, even if not the source of the problem I think it’ll be good to have the gc on it anyway. I read somewhere to isolate the detector heating lines with foil, might try that as well.
Honestly I’m not sure how the baseline should look. This is the cleanest I’ve gotten it on this machine.
I’ll be in the lab today playing with it, maybe something illuminating will come through. I’ve got another column and more detectors to try and isolate the issue
try a run with no injection at all and see what the baseline looks like
Lol that was injection less. Though i think it followed the end of another injection. Running 3 blanks back to back after plugging into the power conditioner, we’ll see shortly!
Noticing on the power conditioner showing the voltage drops from 118 at the start to 113 at the hottest part of the method. Wondering how much of a factor that is as well. I might have to move things around.
Here we go, 3 blank runs back to back. 
Is this manual injection? Sometimes the septums get contaminated.
Auto sampler, those were all blanks though, no injections
Not when you work with solventless 
Septum definitely dirty, replaced it. Now I’m wondering why the auto sampler seems to have inconsistent injections (same 1ul volume each)
The one in the middle is more what I would expect but now I’m getting these large hump and signal response is much higher, despite going down in ppm’s on the standards I’m running. Almost looks like something with the split vent/ratio but its unchanged and pressure based.
9 injections later, 4 were usable, pretty happy with how its turning out.
This seems like a statement in favor of “blanks”.
Would you agree @Cassin?
If you haven’t, y’all should check out the rest of I bought a thing!: Adventures with a 20-year-old GCMS
100%.
Blanks are super important to make sure that your method is solid and you are not getting overflow between samples.
Blanks are also important to make sure your system isn’t gunked up.
And of course - blanks are super good when you run unknowns because that way you know that what you are seeing isn’t overflow from something weird and you started with a blank slate.
A few other things to keep in mind with GC, inside the GC inlet there is usually some kind of glass wool liner. If you are concerned about inconsistent injections or something dirty in the inlet besides the septum, you can take the inlet apart and replace this liner as well.
I was an analytical chemist for most of my career prior to getting into cannabis, feel free to DM me if you want to do some troubleshooting, I’m happy to help.
Edit: Just noticed I said few and just listed one other option. Long day sorry. Here are some other things to look at: Are you doing a needle wash before/after/both for each injection? I assume you’re using high purity air, there’s always the potential of contamination in the air lines.
Your calibration curve looks pretty good for what was usable so the system looks like it’s definitely working well enough, probably just some small cleaning or parameter issues to improve the consistency and repeatability between injections.
