relative response factor agilent micro gc

I change the septum and bakeout the system every week, so I don't think that's the problem. (Although, as you said that could be due to a loss of sensitivity.) The signal response has actually been decreasing over time. In fact, I've been running the same sample over a period of days to see what happens. But according to literature, that doesn't occur until temperatures around ~400C, and even then you need a catalyst.

I wondered about the possibility of MeOH oxidizing to form HCHO, as well. Thanks to both of you for your responses. If you don't want to tune/recalibrate so often, maybe you could use some ISTD to compensate for sensitivity change (but with molecular weight close to that of your compound). We do have some problems with our MS (LC-MS/MS system), with sensitivity slowly drifting (decreasing), so we tend to use freshly tuned instrument, and *always* recalibrate after the tune. However, I wouldn't expect 5x increased signal, unless your instrument was previously really out-of-tune (no pun intended!). Yes, tuning can change the response, due to changes in electron multiplier voltage, mass axis assignments, and, I guess, other ion optics' settings will also affect the amount of ions reaching the detector. Generally, your blank signal shouldn't be more than 10 % of sample.ģ. 'The blanks were slightly lower than the spiked samples, so I figured I could just subtract the blank off'. Is it possible that your MeOH contains traces of HCHO (maybe try running parallel reaction with MeOH of some other manufacturer)? Or, maybe, some oxidation occurs (MeOH -> HCHO)?Ģ. OK, I never run the HCHO-PFPH reaction myself, but I'll try to give some suggestions. My question: is this change in day to day response factor due to the autotuning of my GC/MS or is it something else? I'm totally at a loss as to why I can't get the same results from one day to the next. This is roughly 5 times bigger than yesterday's response. I autotuned the machine, and ran a 50 nanomole sample. Today I came in hoping to replicate my results from yesterday. The blanks were slightly lower than the spiked samples, so I figured I could just subtract the blank off. Second of all, last night I ran 4 samples, two of them were blanks and 2 of them were 50 nanomoles of HCHO. I put the diluted HCHO/methanol (5 microliters in total) into a glass bulb which evaporates the solution, and then passes it onto my PFPH soaked desorption tube.įirst of all, the methanol reacts with the PFPH for some reason, giving a large blank size. I'm using methanol as a dilution solvent for the HCHO because I want to look at nanomolar concentrations. Put briefly, I'm using PFPH to derivatize formaldhyde and thermally desorbing it into a 450 gc 200 ms. I've been trying to calibrate this method for 2 years.

Relative response factor agilent micro gc