GC-FID lower levels
Posted: Tue Jul 11, 2023 6:57 am
So I hope someone can help me, I work in a lab where I’m trying to develop a new method everything has worked great except when we started analysing our samples that we sent away as well we got some major differences in the results, specifically when it came to the later peaks in my chromatogram that read much lower for example my result should be round about 40 ppm but I get 5ppm. I opened up a new mix and now get for 350 ppm round about 100ppm and for a 500ppm round about 300ppm. These values are only relevant to my last two peaks in the mix, the rest of the peaks I get round about 485ppm to 498 ppm.
At first I thought it could be the initial mix, but why would the other components in the mix be fine except for the last two components.
My run is about 17 min, and I’m working at a split of 10:1. I tried a split of 30:1 as well but the results remained similar.
Update edit:
I am trying to analyse Terpenes for Cannabis specifically, I tried with a HeavyWax column and have now tried with a MS 5 column as suggested by someone else. The problem now is that I am getting double peaks at the start of the run and nice sharp peaks start forming half way through.
As for the question of if I’m testing it as unknown or as calibration I did both but just comparing the areas was also a solid indication that somewhere I’m losing the last components.
Its a brand new opened mix from Spex that I had used the first time, I posted my dilemma
Let me know if you need any other information that might help you understand things better.
Is it possible that I’m getting bad double peaks because my oven temperatures at the start is not right?
For the MS-5 column my parameters are as follow:
-Inlet Temp : 230C
-Split @ 1:10
-flow 2,5ml/min
-Oven ramp:
start @ 50C hold for 0.75min
increase to 240C at a rate of 30C and hold for 5min
-Detector temp: 300C
When I used the heavyWax my parameters where:
-Inlet Temp : 200C
-Split @ 1:10
-flow 1,3ml/min
-Oven ramp:
start @ 50C hold for 0.75min
increase to 240C at a rate of 30C and hold for 5min
-Detector temp: 300C
The components I specifically had trouble with when it came to the HeavyWax column was cis- and trans-nerolidol, alpha-bisabolol and guaiol
Now it the ms column the double peaks is basically the first 13 components out 23 components that I’m trying to analyse.
Another edit:
My solvent is ethanol and I inject only 1ul. I usually try more than one way of applying the calibration curve I’ve seen different things definitely need a different way of being processed than others.
I’ve changed my oven temperatures using a method based on a MS column that is similar to the one I currently have. It looks a lot better so far but I will post the link to the method and my full findings of if it really is better or not.
At first I thought it could be the initial mix, but why would the other components in the mix be fine except for the last two components.
My run is about 17 min, and I’m working at a split of 10:1. I tried a split of 30:1 as well but the results remained similar.
Update edit:
I am trying to analyse Terpenes for Cannabis specifically, I tried with a HeavyWax column and have now tried with a MS 5 column as suggested by someone else. The problem now is that I am getting double peaks at the start of the run and nice sharp peaks start forming half way through.
As for the question of if I’m testing it as unknown or as calibration I did both but just comparing the areas was also a solid indication that somewhere I’m losing the last components.
Its a brand new opened mix from Spex that I had used the first time, I posted my dilemma
Let me know if you need any other information that might help you understand things better.
Is it possible that I’m getting bad double peaks because my oven temperatures at the start is not right?
For the MS-5 column my parameters are as follow:
-Inlet Temp : 230C
-Split @ 1:10
-flow 2,5ml/min
-Oven ramp:
start @ 50C hold for 0.75min
increase to 240C at a rate of 30C and hold for 5min
-Detector temp: 300C
When I used the heavyWax my parameters where:
-Inlet Temp : 200C
-Split @ 1:10
-flow 1,3ml/min
-Oven ramp:
start @ 50C hold for 0.75min
increase to 240C at a rate of 30C and hold for 5min
-Detector temp: 300C
The components I specifically had trouble with when it came to the HeavyWax column was cis- and trans-nerolidol, alpha-bisabolol and guaiol
Now it the ms column the double peaks is basically the first 13 components out 23 components that I’m trying to analyse.
Another edit:
My solvent is ethanol and I inject only 1ul. I usually try more than one way of applying the calibration curve I’ve seen different things definitely need a different way of being processed than others.
I’ve changed my oven temperatures using a method based on a MS column that is similar to the one I currently have. It looks a lot better so far but I will post the link to the method and my full findings of if it really is better or not.