Volatile fatty Acid analysis

[ziarehman]

Hello Everybody,

I am new to this forum and also to the world of chromatography. i have started working on a method to analyze wastewater for Volatile fatty acid analysis using headspace chromatography. In the lab we have a GC-MS from the company Thermo Scientific with Thermal conductivity detector (TCD). I would like to ask if somebody could refer me good literature or book, so that i could atleast start in this regard. As i said i just started this work and there is not much available on internet. VFA analysis using FID detector are very common and easily available but not the TCD.

Hope to hear some good advice from the experts on this forum.

Regards!

[CE Instruments]

You have a GC with TCD. Packed column? No MS ??
TCD is designed for permanent gases, and is not very sensitive. It is very unlikely that the system will be of any use. What model Thermo GC? Does it have a base body that you could add an FID to?

[Peter Apps]

If you really do have a GC-MS ( a gas chromatograph connected to a mass spectrometer) with a TCD as well, then your easiest option might be to use only the MS and apply any of the FID methods. With the the MS you have the advantage that you can detect formic acid, which is almost invisible by FID.

If (as I suspect) you do not have an MS, then you will probably have to try to find some packed column methods, since a TCD is not as sensitive as an FID and unless you have high concentrations of the acids it will probably not be sensitive enough to use with a capillary column.

Peter

[ziarehman]

Hi,

Thanks for the reply. Sorry for this little confusion. We have a GC MS module in the lab. not just GC.
That means i take any method available in literatur using FID and apply that in my case??

Thanks for your quick response.
Regards!

[Peter Apps]

Hi,

Thanks for the reply. Sorry for this little confusion. We have a GC MS module in the lab. not just GC.
That means i take any method available in literatur using FID and apply that in my case??

Thanks for your quick response.
Regards!

Let me elaborate slightly. If the GC and MS are properly set up, maintained and operated then methods that work with an FID detector will be very likely to work with the GC-MS with only minor changes in conditions. If it is at all possible you should get some training on how to operate and maintain the instruments.

You mention headspace sampling - how do you plan to do that ? Do you have a headspace sampler coupled to the GC ?

Peter

[ziarehman]

Yes that's the next big problem. We dont have the auto sampler at the moment. That means we are going to inject the samples with the help of syringe. As of things stand today i haven't touched the instrument till now. But gonna play with it in some days. And hopefully then i will be able to ask more technical and specific questions. Thanks once again for the reply.

[MSCHemist]

Yes that's the next big problem. We dont have the auto sampler at the moment. That means we are going to inject the samples with the help of syringe. As of things stand today i haven't touched the instrument till now. But gonna play with it in some days. And hopefully then i will be able to ask more technical and specific questions. Thanks once again for the reply.

That shouldn't be a big deal as long as you use an internal standard and have a good injection technique. For sample prep you could probably use an anion exchange SPE column to clean and concentrate. Spme is also another possibility. I see acids doing manual SPME using a 2cm carb/dvb/pdms column all the way up to stearic acid though sensitivty decreases as the carbon length increases. It also depends on how quantitative you want to be.

Another interesting sample prep is to derivitze with ethyl or methyl chloroformate to form the esters then extract with hexanes. That results in a simple procedure with an easy aqueous derivitization with cleanup via extraction.
http://alexandria.tue.nl/repository/fre ... 619857.pdf
http://www.ogeochem.jp/pdf/ROG_BN/vol27/v27_pp91_95.pdf