How to determine amount of methanol in an aqueous solution?

[madroc]

For a synthesis of methanol I'm doing, I need to find the concentration of methanol in an aqueous solution. The magnitude of methanol is in a few micromoles/L range. I've seen plenty of ways to do it with gas chromatography but my college doesn't have one that supports that magnitute of methanol. Are there any other ways to do it?

Thanks.

[chromatographer1]

Here are generalized ranges for the determination of methanol.

direct injection 1000ppm to 100% GC-FID

headspace 1ppm - 1000 ppm GC-FID

SPME 1 ppb - 1 ppm GC-FID

GC-MS 1ppt - 1ppb

I hope this answers your questions.

Rod

[madroc]

Thanks for the reply. Actually I was wondering if there are any ways of determining methanol concentration in the umol/L range without the use of a gas chromatograph, such as titration, or anything else really.

[JTM]

so you want stuff other than chromatography? heh.

[chromatographer1]

I would suppose if the mixture was PURE methanol and PURE water ONLY, then you could perform a refractive index or density to determine the amount of methanol, but your measurements would have to be extremely accurate.

Even the amount of dissolved air might have enough influence to vary your measurements in these cases.

A simple titration would be great but I don't know of any method to tritrate an alcohol in the presence of water.

Good luck,

Rod

[madroc]

Admittedly this isn't chromatography but I've been looking in papers for hours and wasn't sure where else to look.

Thank you Chromatographer. Unfortunately, there will be several other components in addition to methanol, so that won't work as you said.

[JTM]

can you measure the vapor pressure of the solution? that might lead to a way to do it.

[HW Mueller]

Spectrometry?

[lmh]

I can't remember if methanol is a good substrate for alcohol dehydrogenase. If it is, then you could do an enzyme coupled assay looking at reduction of NAD to NADH. I've done it for ethanol, where it's very easy and very sensitive (if you have a good UV spec at 340nm).

[GeorgeKirke]

I suspect that different concentrations of MeOH would change the surface tension of the mixture so you could try that. No idea whether the effect would be measurable with these concentrations though (or if you have the apparatus).

G

[zokitano]

I can't remember if methanol is a good substrate for alcohol dehydrogenase. If it is, then you could do an enzyme coupled assay looking at reduction of NAD to NADH. I've done it for ethanol, where it's very easy and very sensitive (if you have a good UV spec at 340nm).

Imh you're right. Methanol is a substrate for alcohol dehydrogenaze enzyme. The problem is that this enzyme tends to bind ethanol stronger than methanol. So if you have ethanol in the sample definitely will interfere with methanol analysis. It is well known in toxicology that, the effects of poisoning with methanol can be reduced by ingesting higher amount of strong alcohol (ethanol) drinks. Ethanol instead of methanol will bind the dehydrogenaze, and will prevent transformation of methanol to toxic formaldehyde. During that time, methanol could be excreted from the body in unchanged form.