Can we use N2 carrier gas for ethylene detection

[ismawanto]

Hi, I want to measure ethylene level produced by my plant (I grow my plant in a jar and draw the air sample from the jar). We have Agilent HP PLOT-U column and Agilent 7890A GC system. This GC system uses N2 as a carrier gas. And this is the only carrier gas available in my Lab. Can I use N2 as a carrier gas for ethylene analysis? Anyone has experience in ethylene analysis with GC and N2 as carrier gas? Thank you in advance.

Regards,

Isma

[kchat79]

What detector do you have? If your GC has flame ionization detector (FID), you can certainly detect almost any hydrocarbon with nitrogen as carrier gas.

[ismawanto]

FID detector

[ismawanto]

Since I am a newb and all of my reference methods use He as carrier gas, so I really don't have any idea how to set the method (such as flow rate, oven temperatur etc.) if I use N2 as carrier gas.

[chromatographer1]

Using an appropriate carrier gas flow for a capillary column, just set the FID flows according to the manual and you will be fine. If you flow more than 50mL per min through the plot column (10 times the expected flow) might cause the flame to be hard to light. Otherwise, you should be fine.

best wishes,

Rod

[ismawanto]

Dear Rod,

First, the manual of HP PLOT-U column for hydrocarbon gas analysis only mention about:
Oven : 60°C for 7 min
60-180°C at 10°C/min
Inlet : 180°C, Split ratio 30:1
Detector : FID 200°C
Sample : 5 μL HC
There is no information about carrier gas and the flow rate.

Second, I use different type of sample. In this method I think the sample is liquid (5 μL HC), but for my case the sample is gas (1 mL air sample). Do you think I can use the same split ratio or use splitless?
Thank you in advance.

Regards,

Isma

[chromatographer1]

either

[ismawanto]

Dear Rod,

This morning I run my standard gas (consist of acetylene, ethane, ethylene, methane, carbon dioxide, and carbon monoxide, balanced with nitrogen) with a HP PLOT U column, but I got only 4 peaks. The peak appear between 1 minute to 4 minute retention time. I use the following method:
Oven : 60°C for 7 min
60-180°C at 10°C/min
Inlet : 180°C, Split ratio 12:1
Detector : FID 200°C
Sample : 1 ml air sample

Do you know which standard gas were missing? Are they CO and CO2? Why are they missing? Is it because of the column can not detected those two gas by using this method.
Thank you in advance.

Best regards,

Isma

[chromatographer1]

CO will VERY weakly respond but probably is not separated from the first peak, methane. If you are seeing an air 'peak' (disruption in the flat baseline) then that is where the CO would be if it were detected.

The other 3 peaks are ethylene, ethane, and acetylene.

CO2 does not respond to a FID. You will see it using a TCD. It elutes between methane and ethylene.

best wishes,

Rod

[ismawanto]

Dear Rod,

Thank you for your fast reply.
This morning I tried to measure ethylene concentration from my plant sample. When I injected 1 ml of 1000 ppm and 500 ppm ethylene standard gas I got the peak, but when I injected my samples, there was no ethylene peak. Is it because of the ethylene concentration in my sample very low? Do you have any suggestion?
Should I increase the sample volume?
Someone told me that she use 5 ml to 10 ml air sample for ethylene analysis.

Best regards,

Isma

[chromatographer1]

"Is it because of the ethylene concentration in my sample very low? "

YES

"Do you have any suggestion? "

Your sample is too small or the ethylene concentration is too low.

"Should I increase the sample volume? "

Yes You can try that.

You may have to use packed columns, or use a heartcut multidimensonal chromatography setup to measure the single digit ppm levels. You can also change your split ratio, or try to inject splitless to see the C2= (ethylene) peak.

best wishes,

Rod

[ismawanto]

Dear Rod,

I have tried different split ratio and also splitless injection, but still could not detect ethylene from my samples.
Is it because of my HP PLOT U column not suitable to detect low ethylene concentration?
Should I change my column? Do you know what kind of column suitable to detect ethylene lower than 1 ppm?
I can not find information about the minimum concentration of ethylene that can be detected by certain column.
Thank you.


Best regards,

Ismawanto

[Johnny Rod]

What are the column dimensions? Do you know if Plot U can separate ethylene from all other components? In terms of sesnitivity, we use a 530um PLOT column (different phase) and can see much less than 1ppm when using 1ml injection and 10:1 split.

[chromatographer1]

Sounds like a column problem.

You should have a multidimensional GC if you intend to use packed columns. A good capillary will give you the sensitivity you require according to others on this site.

Good luck,

Rod

[AICMM]

ismawanto,

The fact that you can see 500 or 1000 means the column and detector appear to be working at least marginally. At 1 mL and 500 ppm you should have a very large peak (one that may even be distorted due to loading.) If this is not the case then something else may be going on.

Regarding splitless and split injections with syringes and large volumes. It is advisable to stay with split when shooting large volumes since you can easily over pressure the inlet and force your components places that it should not be. Perhaps something as low as 2:! or 3:1 split is possible? Also, shoot slowly or, better yet, use a valve injector.

It would be nice to see a chromatogram of the 500 if you have one available. Johnny Rod, I think it would be instructive to see the chromatogram you mention as well if you have one available.

Best regards,

AICMM