Calibration curve for SCFA

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

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I'm quite new to GCMS and on my first use I had a strange problem (strange for me).
I injected SCFA's standarts with water as a solvent. I also used formic acid in order to lowered the pH.
This protocol has been used once before at our lab few month ago and it had good results (very nice peeks) when the acetic acid was the first to be out of the column then: propionic acid, isobutyric acid, butyric acid, 2methylbutyric acid, isovaleric and valeric acid. Actually, I guess the formic acid was the first to go out but they didn't see it because the "solvent delay" option.
last week I tried to do it again and I got another picture when the acetic acid went out first, then formic acid (which masked the propionic, isobutyric and the isobutyric acid) and then I saw the peeks of the rest (2methylbutyric acid, isovaleric and valeric acid)
It's reasonable to think that formic acid will go out first from the column and it doesn't happen, I spent a whole day trying change the settings.
Any idea's
I'm interested in the answer you get. I'm currently investigating SCFA, but using Diethyl Ether as a solvent.
You're not seeing formic acid; you're scanning through water. Your scan low mass is too low; set it above water. Typically you wouldn't scan below 33; that way you avoid water and air.
Mark Krause
Laboratory Director
Krause Analytical
Austin, TX USA
godiet.rafi wrote:
I injected SCFA

4 decades in the industry and I had to look up SCFA on Google....
I use headspace insitu esterfication for short chain fatty acids. 5ul sample 5ul H2SO4 10ul alcohol of choice usually methanol and 120deg for 60 minutes and inject headspace with esters. I use an internal standard (4-me pentanoic).

I've looked at free fatty acid columns but have always been fanatically against injecting water especially since my samples are typically loaded with salts, carbohydrates, and protein. How do you avoid fouling the GC?
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