By Anonymous on Monday, June 21, 2004 - 07:01 pm:
Hi Guys:
I am having a problem on a UPS ID test on a new lot of Boric acid, (raw materials).
The monogram states that solutions of borate when combined with 1ml of Polyvinyl alcohol and a few drops of Iodine TS alond with a few drops of HCL with turn intense blue.
The problem I am having is the Polyvinyl alcohol is not soluble in water, the method call for a 1:50 solution. I assume they mean water. And I get a yellow green color.
I know this is not the correct topic to post under, but I would appreciate any help on this matter.
Thanks
By Anonymous on Tuesday, June 22, 2004 - 01:19 pm:
You can use a potentiometric method to analyse your boric acid. Take a pH electrod and dilute NaOH and measure the pH value when you pour the NaOH solution, then you can quantify the amount of boric acid.
I hope this solution can help you
By Anonymous on Wednesday, June 23, 2004 - 07:57 am:
suggest that you dissolve the PVA in solvent MeOH first. then dilute with water
By Anonymous on Thursday, June 24, 2004 - 05:51 pm:
Great Idea
will give it a try
thanks
By Chris Pohl on Saturday, June 26, 2004 - 03:03 pm:
Actually, polyvinylalcohol isn't very soluble in methanol. It's quite soluble in water but there is a trick to getting it to dissolve in water because of intramolecular hydrogen bonding which prevents it from dissolving in water at room temperature. If you add polyvinylalcohol to water which is boiling or near the boiling point it will dissolve in a few seconds. At room temperature it won't dissolve, even in a few weeks!
By AlfredL on Sunday, June 27, 2004 - 12:26 am:
Chris is right about using hot water. I would also recommend to use water at approx. 80-90 oC to avoid hydrolysis of PVA. Note that it takes time to dissolve this material (>30 min).