quantifying water

[WK]

Dear All,
I was wondering if a TCD was suitable detector for determination of water.
How do you get on with it?
The likely interferences will be pigments,ethanol,propylene glycol,isopropanol.
Is there another reliable way?
thanks in advance for any replies
WK

[Don_Hilton]

Depending on your concentration range, you should be able to measure water with a TCD. However, if you have pigments - they are not likely to make it through the GC system. Small quantities can be allowed to collect in an inlet liner with something like a plug of glass wool - but significant quantities will require a different approach. So the next question what are you trying to measure and what is the matrix?

[WK]

Hi Don,
Matrices are natural product extracts - alcohol and CO2 extracted generally.
Regards
WK

[Don_Hilton]

If you are looking at measuring water at about the 85 to 90% level in the mixture and the alcohols at percentages down to about tenths of a percent - you may have a shot with the TCD. This would leave you working with a fairly wide dynamic range.

As I start to type in an idea for a column type, The whole thing depends on the analyte list -- and a bit more information about the matrix. (Plant extracts come in many forms.) And expected concentrations are important.

If you are just measuring water and the other stuff in the mixture makes up more than about 15% of the mixture, I would look at getting a Karl-Fischer titrator. You can use small samples and the alcohols you describe as being present do not interfere with the measurement.

If you are looking at a fermentation broth, take a quick look through the archives on this site. I recall seeing a discussion of measuring water in the past few months.