Peaks not coming in FID run.

[premrrs@gmail.com]

Hi dear all,

This is my first post in this forum. We are using Agilent CG 7890A series. Recently there was problem of front inlet pressure drop (FID). The problem was resolved after we have changed Electronic Pressure Controller (front EPC). Now another problem what we currently facing is of Peaks not coming while we run our product. Our product is Extra Neutral Alcohol (ENA/Ethanol). Our standard sample contains following compounds - Acetaldehyde, Ethyl Acetate, Acetal, Methanol, N-Propanol, Iso-butanol, and Iso-Pentanol. While we run our standard sample, none of the peaks for these compounds are coming except the solvent peak. We are using CP-WAX 57 CB column and the temperature ramp is as follows:
Initial-45C-hold time 1 min, then 70C at 5 C/min, then 100C at 10C/min, then 180C at 15C/min for 1 minute.

Inlet temp- 200C
Detector Tem-220C
Flow rate-2.5 ml/Min.

We have tried all possible solutions to resolve this issue but not able to resolve. Your valuable suggestions and advise will help us to resolve this issue. Waiting for your suggestions.

Regards

Prem

[tkubowicz]

Hi

It would be easier if you could:
-paste chromatogram
-sample/std details (concentration, solvent etc)
-injection technique (S/SL?)

Otherwise there will be questions "ping pong" between you and forum users.

Regards

Tomasz Kubowicz

[premrrs@gmail.com]

Hi,

Sample is Extra Neutral Alcohol (96% ethanol)
injection technique: Split
Split Ratio: 1:50
Internal Std used: n-Pentanol.

Unable to paste chromatogram image. If you know how to uplaod image here please let me know.

Regards

Prem

[tkubowicz]

Hi

To attach image see link below:

viewtopic.php?f=1&t=2617

Regards

Tom

[Peter Apps]

"Our standard sample contains following compounds - Acetaldehyde, Ethyl Acetate, Acetal, Methanol, N-Propanol, Iso-butanol, and Iso-Pentanol."

To repeat Tomasz's request; what are the concentrations ?

We operate under Rod's law; the more you don't tell us, the more we can't help you.

Peter

[dlbenach]

In case you haven't already, as a quick check, make sure your syringe plunger is attached correctly in the autosampler (assuming you are using an autosampler). I've had a similar problem in the past. Looking at the chromatogram everything looks OK except for the missing analytes because the software scaled the screen to the solvent peak. Looking closer, the solvent peak was a lot less in area than normal. Only a very small amount of sample that stuck to the syringe was all that was injected. Hopefully your problem is something simple like that.

[premrrs@gmail.com]

hi

This is the normal chromatogram of our standard.


and this is the current chromatogram of same standard.

[premrrs@gmail.com]

Hi

We have checked in auto samplers too, there is no issue with the sample volume. Our solvent peak (ethanol peak) is coming but not other standard compounds. I have attached both the chromatogram of same standard. please have a look and give me a solution. Its very urgent for me.


Regards

Prem

[Rndirk]

See the comments of Peter and dlbenach.

We need the concentration of the compounds and the injection volume.

It's possible that the system is not injecting the right amount, the concentration is too low/split ratio too high or most of your sample is not reaching the detector (a leak).

Note that you can rule out issues with the autosampler by performing a manual injection.

[premrrs@gmail.com]

Hi,

Thanks for all your replies, below are the concentrations of our standards
1. Acetaldehyde: 30.89 ppm
2. Ethyl Acetate: 18.00 ppm
3. Acetal: 16.45 ppm
4. Methanol: 31.56 ppm
5. n-Propanol: 80.16 ppm
6. Iso-butanol: 15.94 ppm
7. Iso-Pentanol: 16.04 ppm
8. n-Pentanol: 16.12 ppm (Internal Standard)

I have tried by manual injection too. Same problem persists. I compared the area of solvent peak (ethanol peak) in normal & the current chromatogram, both are similar. I am unable to understand why there is no separation of peaks. Are there any chances of contamination in carrier gas? We use Nitrogen as carrier.

[premrrs@gmail.com]

Hi dear members,

Please advise me a solution. I am waiting for your advises. Hope you all will give me a viable solution for the problem i have mentioned.

[tkubowicz]

Hello

I'd recommend to check inlet:

1.Replace liner, septa, check gold seal, check (replace) split vent trap.
2.Check inlet for leaks - run leak test
3.I would cut 20-25 cm of column from inlet side before reinstallation.
4.Check autosampler syringe (or/and one you used for manual injection) - perhaps is leaking
5.Make sure your flows in inlet are correct

Regards

Tomasz Kubowicz

[Peter Apps]

Hi dear members,

Please advise me a solution. I am waiting for your advises. Hope you all will give me a viable solution for the problem i have mentioned.

If you were paying us to do this work it would be appropriate for you to be chasing us for answers, since you are not, it is not.

I need you to take the trouble to post chromatograms that have the same vertical and horizontal scales - not screen shots of the bottom of the solvent peak.

At a split ratio of 50:1 you are putting less than a nanogram of each component onto the column, so the signal:noise in the chromatogram with the peaks looks reasonable. Was that chromatogram run before or after you had the EFC fixed ?

Have you verified that the split is actually 50:1 by measuring actual flows i.e. not using the flow readouts of the GC ?.

When did you last do inlet maintenance ?

Peter