Benedict's & Biuret

[Sassi]

Hi guys,

Does anyone know what the shelf life of benedicts solution is???

And also for Biuret reagent... are the ratios 0.5% CuSO4:10%NaOH The recipe I have is OLD and illegible, please tell me if I deciphered it correctly!

Sassi

[Whspa]

Hi Sassi.

My Benedict's Solution has been stable for at least 2 years - but it is a commercial solution, not one I made myself.

This is my recipe for Biuret :

Add, with stirring, 300mL of 10% (w/v) NaOH to 500mL of a solution containing 0.3% CuSO₄5H₂O and 1.2% sodium potassium tartrate, then dilute to 1L.
This reagent is stable for a few months but not a year. Adding 1g KI per litre and storing in the dark makes it stable indefinitely.

Hope this helps.

Carol

[ellice]

Hi Sassi,
From experience, Benedict's does go off, but I must admit, the stuff was old! I now test what's in the bottle before it goes out to the classroom.
Ellice.

[lada]

Hi, I have a great recipe for biuret soln.
Solution 1 1%copper sulfate
Solution 2 2M sodium hydroxide.
Solutions are used separately and I keep them in dark dropper bottles.
First add 1ml of solution 2, then 1 drop of solution 1 to about 2ml of sample being tested.
Positive reaction for protein will give colouchange from blue to violet(mauve).
This recipe is from the Laboratory p 115.
It is good as it will last without preservatives, because its not mixed.
Lada

[Sassi]

Ahhhhhhhhhhhhhhhhhh the Laboratory!!! Why on earth didnt I think of that

Thanks for all your help, Ive checked my benedict's and it seems to be working fine!

Only one more day to go to the weekend

[ELIZABETH]

Hi All,
Re the Biuret test; I use sodium carbonate instead of sodium hydroxide - gives a better result and is safer to use.
Liz

[Sassi]

Hi Elizabeth,

Do you use it in the same proportions as the recipe by lada, ie. do you just substitute sodium hydroxide to sodium carbonate? I might make up both and try them out to see which one works the best.

[ELIZABETH]

Hi
Yeah, I use the same conc. and quantity and always get a good colour change.
Cheers

Liz

[lada]

Hi Sassi
let us know the result. I would love to change from NaOH to carbonate.
Lada

[lada]

Just a question. If students get a question regarding test for protein and they have to name the chemicals, the sodium carbonate would not be the right answer, or would it??