Re: why is solid iodine not considered a good standard solution

Iodine is considered a good standard solution but I think sodium 
thiosulfate is to enhance the ability of the solution to detect smaller 
amounts of Ascorbic acid in the solution or tablet in your case.  Therefore 
this addition may be better.  BUT, if you have a large amount of Ascorbic 
acid in what you are measuring the use of iodine may be good enough.  I 
measure Ascorbic Acid in things like blood and tissues in the body so I 
need to have a better or lower detection limit! 

I work with an HPLC  (High Performance Liquid Chromatography) method.  This 
method measures all the forms of Vitamin C that are used by the body for 
this vitamin.  Usually, people don't realize that when we talk about 
vitamins we are talking about several chemicals that are used by the body 
for Vitamin C.   (The different forms are: Ascorbic Acid, Isoascorbic Acid, 
Dehydro-L-Ascorbic Acid, and Dehydro-D-Isoascorbic Acid.