MS or TCD

[loic2810]

Hi,

I ve to set up Ethylene analysis and i can choice the system GC in order to do it.

I thought taht GC /TCD should be suitable to do this but i ask me some questions:

Is GCMS would be more interesting to do it? suitable to ethylene analysis with the same sensitivity of TCD?

Is TCD need special gaz as mobile phase?

Thanks a lot for your response.

[chromatographer1]

Very few use a MS for ethylene analysis. The COST of a MS gains you little except lower detection limits. Do you really need to spend tens of thousands of dollars initially and similar amounts for service every year for no good purpose?

The TCD will adequately measure down to the 0.01 % level.

Do you need lower levels than that?

best wishes,

Rod

[loic2810]

HI thanks for your response.

You re right , if tcd can do it no need to spend a lot of money in MS. But of course, the new GC will have other applications that could need sensibility and identification by MS.

It why i ask me this question.

But firstable, i need a GC TCD AND FID (both detector) wich have quite the same price as GCMS.

[chromatographer1]

Most ethylene analysts want CO and CO2 amounts in less than 100 ppm amounts, often less than 1ppm. FID with a methanizer is recommended.

Acetylene is measured at levels below 1 ppm. FID is recommended.

MS might do CO2 but CO has a difficult mass range to measure.

CO at less than 1 ppm means spectroscopy is recommended.

If this is not a plant process analyzer then you can always add a MS later as needs become known.

You could omit the Tcd and FID and get a helium ionization detector instead.

Lots of possibilities, it depends upon the entire extent of your needs. Only you know the answer.

best wishes,

Rod

[willnatalie]

"but firstable, i need a GC TCD AND FID (both detector) wich have quite the same price as GCMS." - look into the SRI instruments if all you need to do is simple work. They have one already configured and pretty good. I have two.

http://www.srigc.com/2005catalog/cat03.htm

Multiple Gas Analyzer #1 GC is a good choice.


good luck.

[AICMM]

loic2810,

If looking at impurities in ethylene, you are probably looking at fairly light components (CO, CO2, acetaldehyde, acetylene, etc...) which is not where MS particularly shines over GC. If you are looking at trace impurities, TCD is not really the detector that shines for that kind of work since it usually sensitive down to 10's or 100's of ppm and I suspect you want to go lower than that.

Therefore, I would suggest GC with an FID keeping in mind Rod's comments about a methanizer if it will get you low enough detection limits for CO/CO2. If not, HID will certainly get you down low enough for CO/CO2 but the chromatography has to be clearly defined since the HID will also see everything else you might inject. This is not a simple system so getting professional advice (and probably a professional build) is good advice.

Best regards,

AICMM

[loic2810]

Hi AICMM

Thanks a lot for your response.

My goal is to analyse and quantify ethylene from fruits or vegetables.

So i need a GC able to detect and analyse only ethyle for this application. But it's just for one study, otherwise this future GC will have to be able to analyse other various components that probably won't need TCD detection.

So i m trying to find a GC able to do this 2 sorts of applications.

I m probably not very clear lol

Thanks

[chromatographer1]

I would suggest you get the tools (cheap by the way) to perform manual SPME. (See Supelco technical service)

Add any std GC with an FID and use a 3-6ft Porapak Q column, packed not capillary.

That is all you need to do very low to moderate levels of ethylene which is what you need.

best wishes,

Rod

[loic2810]

Hi
chromatographer1


Thanks a lot, i will see Supelco, great idea.

[AICMM]

loic2810,

Keep in mind that ethylene is mass 28 and nitrogen is mass 28 so that presents a challenge when using MS. Also, ethylene is very light so a column that will be able to hold it may be a column that does not match well with typical MS systems. At first appearance, it still seems like a GC/FID might be your best bet.

Best regards,

AICMM

[loic2810]

Hi AICMM,

Thanks again for your response.

FID so will be probably the best choice with a specific gas column.

Best regards.