Maybe you can perform a classical (look for the SOP) Chemical Oxygen Demand (COD) method if no other organic compound is in the water. Purge N2 through the boiling solution and collect the formed CO2 from your methanol in 100 mL exactly 100 µM KOH. After complete oxidation titrate back with a 100µM H2SO4 standard-solution. From the amount neutralized KOH calculate the amount of methanol.

Alcohols are transparent above 200nm, however λmax for methanol is 177 nm. Could you use a UV spectrophotometer at 177nm?

I also have a relatively high concentration of DMSO (0.1M) which has a broad absorption in the UV.

Have you thought on alcohol oxidase which will produce formaldehyde and H2O2 if oxygen is present in the solution? Either product can be measured photometrically with known reagents.

Thanks for your response Karl. I know very well the method for determining formaldehyde ("Hantzsch reaction") and used it successfully in the past. But how do you ensure oxidation of methanol to formaldehyde and not going also to CO or formic acid ? How can you control the reaction?

It might be that the Hantzsch reaction prevents a further oxidation of the formaldehyde.

But what about an alcohol detection with ceric nitrate? “Alcohols react with ceric nitrate reagent to produce a color change (yellow to red) whereas carbonyl compounds do not react. Note that changing the groups attached to certain inorganic ions such as Ce 4+ results in a change to the electronic structure, which results in a color change. Production of a magenta color therefore indicates the presence of an alcohol group.” Due to the low concentration it would need a long optical pathway cuvette (> 5cm) if it will work at all.

Thanks for your help Karl. I would love to have an article or patent about colorimetric alchol detection using ceric nitrate (I hope that DMSO will not interfere with the analysis..) . My e-mail address: [email protected]

Please read the attachment; DMSO when activated is a weak oxidation reagent.

I'll read it. It looks pretty good. By the way, I found a simpler method, quite new, which was published in Chinese journal. See Attachment.

You could consider this approach when you have access to a GC/MS system with headspace sampling unit:

Hu et al. j. Ind.Eng. Chem (2012) http://dx.doi.org/10.1016/j.jiec.2012.11.12

Depending on your sample size, I could suggest you several analytial procedures: distillation, thermogravimetry (differencial thermal analysis), GC (several detectors, not only MS) or indirect UV-VIS valoration taking the opportunity of the reaction between EtOH and Cr2O7-- (440nm) and the Cr(III) resulting (605nm)

If you have a GC wth FID or MS facility and if you also aware of SPME (solid phase microextraction) technique then go for that.

I have not tried this, but the measurement of refractive index relative to standards might be of adequate sensitivity fro application to the determination of methanol in aqueous solution. Srecno, Katz

Hi,

Methanol concentration can be determined by gas chromatography, using a Flame Ionized Detector.

Hi Ronen Bar-Ziv and Henricus Verhoeven...I can't download the article. Can both of you please send me the articles to my [email protected]..

 Did any of you try the Nitroprusside assay? I tried it but I don't get any color reaction. The reaction is very simple so I am starting to doubt it actually works since it is not documented at any other source.

 Hi Joroen, As far as I remember I tried a long time ago the Niroprusside method with the same result you got, so I doubt if it works. 

I have tested this method for methanol production from PEC reduction of CO2. provided the quantity of of the methanol is high enough to an extent it is measurable by this method, then its good to follow. But from my experience, methanol produced from CO2 reduction was not detectable by this method..but GC does.

It may be possible to make use of physical properties such as: density, refractive index, freezing point, et cetera to measure the concentration of methanol in aqueous solution.

What about enzymatic methods? One method is based on alcohol oxidase followed by formaldehyde dehydrogenase. It can specifically detect methanol and not other alcohols (e.g., ethanol) and is colorimetric.

For determining the methanol concentration of a liquid solution from its refractive index has been reported in the article by nondestructive measurement technique based on a laser interferometer. The optical metrology system is employed to measure the refractive indexes of samples with known methanol concentrations ranging from 0 ~ 90%.

"The measurement of the methanol concentration of liquid solution based on laser interferometer, DOI: 10.1109/3CA.2010.5533499"