[ROSETTA]

Hi there, can anyone help.
I have seen some posts online where coulometric Karl fisher is done with HPLC grade methanol and a blank taken and the value subtracted from the value of the sample in methanol. However, most literature is with anhydrous methanol (which must still absorb moisture) and a blank taken.  Is the use of hplc grade methanol less accurate for this test. Why- is it to do with moisture adsorption from the atmosphere
Thanks
Rosie

[ferrox159]

Anhydrous MeOH has <0.002% water and HPLC Grade has <0.03% water.  Which you choose for your Karl Fisher Application would depend on the criteria you have to meet for your samples. Meaning what is the RSD you have to meet.

Which MeOH you use can make or break the analysis.

Anyone I know in pharma performin KF analyses in QC where raws have to be analyzed will/may only use anhydrous grade. 

Sima Aldrich has an excellent site where you can check the specs on all grades of various solvents used for typical applications.  The different providers are even cross referenced. This reference is often used by most for determining which solvent/grade is appropriate to a specific application.

LINK-METHANOL: http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Methanol_Center/Specification_Comparison.html


General link for solvent selection wih regard to application: 
http://www.sigmaaldrich.com/Area_of_Interest/Research_Essentials/Solvents/Methanol_Center.html

I have attached a copy of the KF METHOD for the Determination of Water Content

Here is the link to the pdf:  http://www.who.int/whopes/quality/en/methodm7.pdf

[nauticar]

Hi there, can anyone help.
I have seen some posts online where coulometric Karl fisher is done with HPLC grade methanol and a blank taken and the value subtracted from the value of the sample in methanol. However, most literature is with anhydrous methanol (which must still absorb moisture) and a blank taken.  Is the use of hplc grade methanol less accurate for this test. Why- is it to do with moisture adsorption from the atmosphere
Thanks
Rosie

As with most solvents, MeOH absorbs moisture readily from the atmosphere. The difference b/w dry (anhydrous) methanol and HPLC grade is the amount of moisture already in the MeOH. I find the moisture data pasted on solvent bottles pretty much useless, because it will definitely change once you open the bottle, or if the bottle has been on lengthy storage, or if the bottle was subjected to improper storing conditions. That moisture value is most probably obtained under regulated sampling conditions from a bulk source. Many variables.

Unless youre doing your analysis in a moisture or low humidity atmosphere, chances are that the MeOH, regardless of grade, will still absorb some moisture. I dont have solid evidence for this, however it is easy to prove (or disprove) in your lab.

So to answer your question, using an anhydrous form of MeOH, instead of HPLC grade, will facilitate your titration -this discussion as you indicated is about coulometry, so therefore I assume that your sample you intend to analyze has micro or milligram levels of moisture present. However in my opinion, as long as there is a blank subtraction used, and the same calculation of blank subtraction is employed in all calculations, there will be no significant difference in the end result if you use either form.

N

[Alpha-Omega]

Just one additional note:  There is a significant difference in a QA/QC Pharma environment.  Only Karl Fisher Grade is acceptable-that is independent of the fact that the blank will account for any differences-in a QA/QC GLP/GMP environment 21 CRF Part 11-to be compliant they have to use Karl Fisher Grade anhydrous MeOH.

Another example of a material QC is pretty picky aout would be NaOH.  In QC JT Baker NaOH is not used.  The preference is Fisher and or VWR.  JT Baker has alot of carbonate in it.  In IC appllications onlt low levwel carbonate NaOH from Fisher is implemented when running carb analyses with amperometry detection.  If this is not done there is contamination and fouling of the system....you will have large dips and evidence of oxgenation in the chromatograms.