Am 18.04.2009, 15:57 Uhr, schrieb Lionel Brooks 3rd
<Lionel.Brooks from dartmouth.edu>:
> Sodium orthovanadate preparation:
> This needs to be done under the fume hood
> • Prepare a 100 mM solution in double distilled water
> • Set pH to 9.0 with HCl
> • Boil until colorless
> • Cool to room temperature
> • Set pH to 9.0 again
> • Boil again until colorless
> • Repeat this cycle until the solution remains at pH 9.0 after boiling
> and cooling
> • Bring up to the initial volume with water
> • Store in aliquots at -20 ̊C
>> Much to my chagrin the solution is not colorless after more than 30 min
> of boiling. Any ideas on what I am doing wrong?
There seems to be an impurity. Adding a spatula of activated charcoal
before the first boiling and filtering afterwards might help. There may
also be a trace of phosphate present, wich gives a yellow tint (or
precipitate, if the concentration is high enough). Make sure that you have
pure reagents and that the glassware is free of phosphate (detergent!)
