Chromatography Forum

Hey,
I use a Agilent (HP) 6890 GC FID where I can't measure any aromatic aroma molecules (estragol, benzaldehyde, cinnamaldehyde,...). I use a HP5-MS and I developped a method with my GCMS which works good for detection but my GCFID only detects terpenoids and small alcohols. I even injected a 1000 ppm estragol standard but I saw nothing.

It doesn't seem normal that I can't detect these molecules. I tried even other colums and different methods.

Is this a hint, that I have to change my FID detector? Do anybody knows where I could buy them for a little price ?

Disclaimer: we only used GCMS for the 2000 aroma compounds we looked for in fragranced consumer products.

GC-FID was used for products that had "active" levels of such component, like menthol, d-limonene, etc.

That said: if such aroma molecules are exiting the column and are at high-enough levels, then FID will detect them.

Hey, yes I have very high concentrations of my aroma molecules in the samples so that I definitly should see anything but after half an year of trying I can say that I only can measure terpenoids and small alcohols with this GCFID.

Normally I use the GCMS for identification but due much higher reproducibilties with the GCFID for quantification (GCMS: R^2 for limonen 0.97 GCFID: R^2 for limonen 0.999) I would prefer the GC FID.

But does everything speaks for the necessity of changing the FID detector?

Regards

If the FID detects terpenoids it will detect all the other organics as well. Therefore the problem is not with the detector. Where the problem is nobody can tell you because you do not tell us anything about your methods. If you want help rather than a string of guesses we need to know; all the temperatures and gas flows, column type and dimensions, inlet liner type and when you last did inlet maintenance, what concentration are you samples and what are they dissolved in, what volume are you injecting, split or splitless, split ratio if split.

Peter

If the FID detects terpenoids it will detect all the other organics as well. Therefore the problem is not with the detector. Where the problem is nobody can tell you because you do not tell us anything about your methods. If you want help rather than a string of guesses we need to know; all the temperatures and gas flows, column type and dimensions, inlet liner type and when you last did inlet maintenance, what concentration are you samples and what are they dissolved in, what volume are you injecting, split or splitless, split ratio if split.

Peter

I apologize for gaving not the whole information needed.

Here is the method for the aroma molecules diluted in propylene glycol in a concentration range from 2000(when not even higher) to 1 ppm. This method is also used at the GCMS which separates the desired aroma molecules in a good way.

Used column: HP5-MS (30m, 250µm, 0.25µm)
T(Inject)= 270 °C 1µl splitless, 1ml/min Helium (constant flow)
new splitless inlet liner original part from agilent, new septum
T(start) = 80(3 min) to 150 with 8 °C/min to 300°C(3min) with 15°C/min
T(FID) = 250 °C
flow(H2) = 30 ml/min flow(air)= 300 ml/min flow(N2)= 30 ml/min
(but I tried different flows of H2 and air but the ratio was always 1:10, quoted by Baars B. in a GC troubleshooting book as the best ratio for the FID)

Thank you

Hi,

If the FID detects other molecules then the detector works.
Have you tried to run the same sample with another column?
or maybe other method?
T(start) = 80(3 min) to 150 with 10 °C/min to 300°C(3min) with 2°C/min

I guess the problem is that you run the ramp too fast 15°C/min from 150 to 300, but off course i might be wrong. Please correct me in that case.

Regarding to Agilents flavour and fragrance database the Benzaldehyde have a rT of 28.976 using a different method and this column 50 m x 320 µm x 1.05 µm HP-5, 19091J-215.

More info here: http://www.agilent.com/en-us/support/so ... flavorsrtl

http://www.agilent.com/cs/library/slide ... abases.pdf


Hope it helps!!

Kind regards,
Alvin

Hi,

If the FID detects other molecules then the detector works.
Have you tried to run the same sample with another column?
or maybe other method?
T(start) = 80(3 min) to 150 with 10 °C/min to 300°C(3min) with 2°C/min

I guess the problem is that you run the ramp too fast 15°C/min from 150 to 300, but off course i might be wrong. Please correct me in that case.

Regarding to Agilents flavour and fragrance database the Benzaldehyde have a rT of 28.976 using a different method and this column 50 m x 320 µm x 1.05 µm HP-5, 19091J-215.

More info here: http://www.agilent.com/en-us/support/so ... flavorsrtl

http://www.agilent.com/cs/library/slide ... abases.pdf


Hope it helps!!

Kind regards,
Alvin

Hey Alvin,

thank you.

In fact I use the same method on the GCMS and it works there very fine. In additon i used at the beginning a very slow gradient 80 to 300 with 2 °C/min and even then I didn't saw anything. I ramp with 15 °C/min at the end knowing that there is no molecule which elutes at these temperatures

Your solvent might be a problem, what happens if you use something volatile like hexane or dichloromethane ?

Some basic trouble-shooting is in order. Check for leaks with a leak seeker, especially from the inlet. Check that your split purge and septum flows are what they should be using a flow meter. Inject some methane or cigarette lighter gas and measure the retention time. Check that the column is inserted to the correct depth into the inlet and detector.

Peter

Your solvent might be a problem, what happens if you use something volatile like hexane or dichloromethane ?

Some basic trouble-shooting is in order. Check for leaks with a leak seeker, especially from the inlet. Check that your split purge and septum flows are what they should be using a flow meter. Inject some methane or cigarette lighter gas and measure the retention time. Check that the column is inserted to the correct depth into the inlet and detector.

Peter

So my GC is totally reproducible for terpenes which speaks for a working system. But as soon that I use estragol diluted in different solvents (hexane, dichlormethane, methanol, acetonitril) I don't get any peak no matter how high the concnetration of my estragol is.

Your solvent might be a problem, what happens if you use something volatile like hexane or dichloromethane ?

Some basic trouble-shooting is in order. Check for leaks with a leak seeker, especially from the inlet. Check that your split purge and septum flows are what they should be using a flow meter. Inject some methane or cigarette lighter gas and measure the retention time. Check that the column is inserted to the correct depth into the inlet and detector.

Peter

So my GC is totally reproducible for terpenes which speaks for a working system. But as soon that I use estragol diluted in different solvents (hexane, dichlormethane, methanol, acetonitril) I don't get any peak no matter how high the concnetration of my estragol is.

Does this mean that you can now see the other aromatic compounds that you had a problem with according to your first post ? Can you detect e.g. toluene or naphthalene ?

Peter

Your solvent might be a problem, what happens if you use something volatile like hexane or dichloromethane ?

Some basic trouble-shooting is in order. Check for leaks with a leak seeker, especially from the inlet. Check that your split purge and septum flows are what they should be using a flow meter. Inject some methane or cigarette lighter gas and measure the retention time. Check that the column is inserted to the correct depth into the inlet and detector.

Peter

So my GC is totally reproducible for terpenes which speaks for a working system. But as soon that I use estragol diluted in different solvents (hexane, dichlormethane, methanol, acetonitril) I don't get any peak no matter how high the concnetration of my estragol is.

Does this mean that you can now see the other aromatic compounds that you had a problem with according to your first post ? Can you detect e.g. toluene or naphthalene ?

Peter

No it's the same problem as in the first post. I only see terpenes down to 1 ppm but no aromatic aroma molecules (which have one or two oxygen) are detectable no matter which concnetration I inject.

So my GC is totally reproducible for terpenes which speaks for a working system. But as soon that I use estragol diluted in different solvents (hexane, dichlormethane, methanol, acetonitril) I don't get any peak no matter how high the concnetration of my estragol is.

Does this mean that you can now see the other aromatic compounds that you had a problem with according to your first post ? Can you detect e.g. toluene or naphthalene ?

Peter

No it's the same problem as in the first post. I only see terpenes down to 1 ppm but no aromatic aroma molecules (which have one or two oxygen) are detectable no matter which concnetration I inject.

Is it the oxygen or the benzene ring that causes the problem - can you see oxygenates with no ring, or rings with no oxygen (e.g. naththalene, touene) ?

Peter

Does this mean that you can now see the other aromatic compounds that you had a problem with according to your first post ? Can you detect e.g. toluene or naphthalene ?

Peter

No it's the same problem as in the first post. I only see terpenes down to 1 ppm but no aromatic aroma molecules (which have one or two oxygen) are detectable no matter which concnetration I inject.

Is it the oxygen or the benzene ring that causes the problem - can you see oxygenates with no ring, or rings with no oxygen (e.g. naththalene, touene) ?

Peter

Yes I think the aromatic oxygen is the problem but i just repaired my MS so that I can quantitate with her so that I don't need the GC-FID anymore but thanks for your advise.

Jean