benedict test result help

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benedict test result help

Post by biomania » Sat Apr 17, 2010 2:35 pm

Hi, i m kinda new to this forum and i have a very puzzling situation with Benedict's test.
I played around with some of the glucose solutions that i prepared in the lab ( 0.1%, 0.2% 0.3% ). I realized that although Benedict test is described as a semi-quantitative test based on the precipitate colour, the difference in speed of colour change is important too. I add 2ml of each sample with 0.5ml of Benedict solution, and i did water bath for 15 minutes and the colour changed, but, it all turned red in the end. I thought it was weird, so i did some control on the temperature.
1st run, using normal water temperature of 27Celcius and heated with all the samples for 10-15 mins until about 70-80 celcius.( all turned red)
2nd run, heating the water till 80celcius and let it dwindle, while putting my samples in it for 10 mins
( 0.1% gives greenish brown, 0.2% brown, 0.3% intense brown)
3rd run, maintaining water temperature from 77 to 83celcius for 10mins ( all samples give brown precipitate with slight difference in intensity)
So, my question is:;
1)Is there anything wrong with my choice of temperature? or heating time?
2) I thought brown precipitate is for concentrated reducing sugars solution, how is it possible to get brown for all results? They are all 0.1,0.2,0.3% only.
3)should i stop the heating/waterbath as soon as the colour intensity is obvious ( all changes colour to green in the first few minutes, but at different intensity, before all changing to brown)?

:mrgreen: thanks!!

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