what's wrong with my anthrone reagent? - (Mar/25/2010 )

I need anthrone reagent to analysis the carbonhydrates in plant seedlings, the formular is:
add 100mg anthrone to 100ml 80% H2SO4.
The trouble is i always get a different colour compared with other guys in my lab: mine is yellow-green(more green then the colour of beer), while others' are brown yellow(just like beer).
someone told me the colour depend on the quality of H2SO4, I changed it but things did't turn better.
Is it owing to the quality of authrone? or there's sth wrong in my protocol?

P.S. i prepared the 80%H2SO4 like this :add 81.6 ml 98%H2SO4 to 18.4ml ddH2O
P.P.S. i add anthrone to 80%H2SO4 when the latter is not completely as cold as room temprature.

Hi there,
When you're preparing anthrone under ice cold condition the colour will be same as you are getting.

Brown colour possibly...
1.Preparing antrone reagent under room temperatue
2.Not giving sufficient time for cooling of freshly prepared 80%H2SO4
3.Anthrone might've oxidized

for any reagents temperature, oxygen and light are crucial.