Chemical Forums
Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: LabProARW on June 24, 2019, 11:42:18 AM
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I am running a method to analyze for Paraquat Dichloride in an aqueous solution. The standard material comes from Sigma Aldrich as PESTANAL grade C12H14Cl2N2 ยท xH2O and anhydrous M.W. of 257.158. Apparently the amount of hydration is unknown or varies as the amount of water of hydration is not specified. How do I report a test result as Wt% Paraquat Dichloride if there is an unknown amount of water in the weight of my standard?
Thanks in advance.
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Does the std come as a solid? If so run a DSC or karl fischer to get water content.
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The standard material comes as a solid crystals at $500 a gram. Karl Fischer would be quite expensive. I suppose if I got several grams from the same manufacturers lot, mixed it up and ran the water, I would have enough standard material left over to use and be able to make use of their certificate of analysis.
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Bake it in a vac oven for 24 hours under reduced pressure. That should get rid of most of the water. If you want to be really precise, you could also do a TGA analysis.
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Great ideas all. How would I know what temperature to bake a hydrate (water locked up inside the crystal) in order to remove the water? Water boils at 212F at STP but if the water is inside the crystal lattice what temperature would you suggest? My guess would be the melting point of the solid.
Thanks
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Either heat it under vacuum or put it under vacuum at RT for a day with P2O5 as I show here
https://www.chemicalforums.com/index.php?topic=99539.msg349639#msg349639.
It appears that it is fairly thermally stable https://nepis.epa.gov/Exe/ZyNET.exe/30003WGG.txt?ZyActionD=ZyDocument&Client=EPA&Index=1991%20Thru%201994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&UseQField=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5CZYFILES%5CINDEX%20DATA%5C91THRU94%5CTXT%5C00000009%5C30003WGG.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=7 (https://nepis.epa.gov/Exe/ZyNET.exe/30003WGG.txt?ZyActionD=ZyDocument&Client=EPA&Index=1991%20Thru%201994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&UseQField=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5CZYFILES%5CINDEX%20DATA%5C91THRU94%5CTXT%5C00000009%5C30003WGG.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=7)
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Many thanks for all of the helpful contributions! Glad I found this forum!
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Gently warm (like 50-60 C) in a vacuum oven overnight should do fine. As long as your substance doesn't decompose, you could go even higher. We dehydrate hygroscopic salts and minerals like this all the time. After you take it out of the oven, store the stuff in a desiccator until ready to use.
If you have an FTIR-ATR handy you can quickly and crudely check for residual water content that way.