September 22, 2019, 09:15:17 PM
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Topic: Method for determining moisture content of alcohol  (Read 335 times)

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Offline nealk7370

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Method for determining moisture content of alcohol
« on: July 17, 2019, 01:19:28 PM »
I am currently having difficulty developing or finding a method for moisture analysis of isopropanol with a range of 0%-20% for moisture content. Is there something like this out there? I have found a few methods but none that are in my desired detection range.


Offline Babcock_Hall

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Re: Method for determining moisture content of alcohol
« Reply #1 on: July 17, 2019, 01:31:29 PM »
Which methods have you looked into, and what were their detection ranges?

Offline nealk7370

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Re: Method for determining moisture content of alcohol
« Reply #2 on: July 17, 2019, 02:19:37 PM »
Three methods I have found that I was able to mess around with, Salting out, Karl Fisher titration and adding IPA drop wise to Xylene.

The first method doesn't purify the IPA past the Azeotrope so it's essentially the same as distilation.
The Karl fisher and the Xylene method doesn't display accurate results under 2% moisture.

Offline wildfyr

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Re: Method for determining moisture content of alcohol
« Reply #3 on: July 17, 2019, 02:39:33 PM »
High field NMR done very carefully?

Offline Babcock_Hall

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Re: Method for determining moisture content of alcohol
« Reply #4 on: July 17, 2019, 03:27:14 PM »
(edited)
I have read about a version of the Karl Fischer method that uses a coulometer, but I know almost nothing about it, other than that it works at lower levels of water.  The NMR method seems reasonable, but one would have to correct for differences in T1 relaxation, which might be one of the thing to which wildfyr alluded.
« Last Edit: July 17, 2019, 04:15:36 PM by Babcock_Hall »

Offline Enthalpy

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Re: Method for determining moisture content of alcohol
« Reply #5 on: July 17, 2019, 04:09:11 PM »
Wouldn't the density suffice?
https://en.wikipedia.org/wiki/Hydrometer
For booze it works, and isopropanol's density differs much from water.

If deducing a mix ratio from the density, beware the mixture may contract like water and ethanol do, so the volume fractions don't simply add.

Offline nealk7370

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Re: Method for determining moisture content of alcohol
« Reply #6 on: July 17, 2019, 04:25:48 PM »
Unfortunately I do not have access to an NMR machine. In the meantime I have been using density to determine the % but was hoping for a more analytical approach with an instrument or something along those lines. I appreciate all the help so far!

Offline OrganicDan96

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Re: Method for determining moisture content of alcohol
« Reply #7 on: July 17, 2019, 04:34:17 PM »
just an idea but could IR be used? make a series of stock solutions of known concentration of water and make a calibration curve based on the absorbance of the O-H stretch of water. then measure an IR of the unknown and determine concentration using calibration curve.

Offline Babcock_Hall

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Re: Method for determining moisture content of alcohol
« Reply #8 on: July 17, 2019, 05:16:40 PM »
Exactly how are you determining density?

Offline rolnor

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Re: Method for determining moisture content of alcohol
« Reply #9 on: July 17, 2019, 08:19:37 PM »
People making moonshine or brewing wine use a hydrometer
https://en.m.wikipedia.org/wiki/Hydrometer
Maybe thats what you have used?
I should be possible to use a strong base like BuLi and an apropriate indicator to se the breakingpoint where all water is converted to OH- and the pH goes up as EtO- is formed?

Offline DrCMS

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Re: Method for determining moisture content of alcohol
« Reply #10 on: July 18, 2019, 06:26:43 AM »
We use potentiometic Karl Fisher titration and get good results down to ~100ppm water. 

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