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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: synthon on March 07, 2014, 09:37:33 AM

Title: How to confirm desalination?
Post by: synthon on March 07, 2014, 09:37:33 AM

Long story short, I neutralized a basic hydrolysis product by stirring it with ion exchange resin in the pyridinium form to exchange Na+ with pyridinium.  Since the pH was neutral, I assume that all excess Na+ had adsorbed to the resin and pushed pyridinium (hydroxide) into the product solution.  After evaporation of the water, solvent and pyridine, I'm left with a residue that looks a bit salty, and now I'm curious what percenatge of the weight is residual salt (possibly 0).

My question is, how can I confirm that the product has been thoroughly desalinated?  I know that conductivity of a solution can determine its ionic strength, but my product exists as an ion, so that probably wouldn't be very helpful in this case.  I know that the 1H NMR will look poorly shimmed when salts are present, without tuning the probe, but that seems rather qualitative and indefinite. I'm also aware of flame tests/AAS which can identify the presence of ions/elements by color, but that seems a bit excessive. I suppose I'm hoping there's a Goldilocks solution to this problem (which isn't really an issue, it's not going to hold up the chemistry).    :)

Any neat ideas?

Title: Re: How to confirm desalination?
Post by: discodermolide on March 07, 2014, 09:42:59 AM

In the Pharma industry we always had to measure the sulphate ash. This is a test for residual inorganic material.
But I suppose you don't have 1g or more?

Title: Re: How to confirm desalination?
Post by: synthon on March 07, 2014, 09:49:37 AM

Just under, ~0.6g

Title: Re: How to confirm desalination?
Post by: TheUnassuming on March 07, 2014, 09:55:57 AM

I didn't know about the sulphate ash test before, interesting to be sure.  Do they still use it much in industry?
Haha, the key with the 1g is that it has to be 1g you don't mind seeing roached.

Title: Re: How to confirm desalination?
Post by: billnotgatez on March 07, 2014, 10:24:17 AM

FYI only - Found this using GOOGLE
http://apps.who.int/phint/en/p/docf/

Title: Re: How to confirm desalination?
Post by: discodermolide on March 07, 2014, 11:14:31 AM

Thanks for the link bill....
As the person responsible for the drug substance production I was always asked to provide analytics with about 50g or so of material from each batch. This so they could keep reference material, validate the method and provide a result!
Apart from one case I can remember this wasn't a problem as we usually had several hundred kilos.

Title: Re: How to confirm desalination?
Post by: Enthalpy on March 14, 2014, 06:39:56 AM

That maybe?
http://en.wikipedia.org/wiki/Isotachophoresis