Can I Make Biuret Reagent at Home?

[jkost]

Hello

i'm trying to make buiret reagant, but probably I'm not mixing the chemicals in the correct way because at first the buiret reagant is blue then it turns dark and if you leave it alone it becomes clear with a black precipitate, it's obvious that I'm doing something wrong while mixing the chemicals, because i don't have a scale I'm dissolving aproximately 1g CuSo4 and 2g NaOH into 50ml water maybe I'm mixing too much or too little amount of chemicals?

thanks!

 

[chemisttree]

Where is the tartrate in your recipe?

 

[Borek]

I think there are many recipes - some use tartrate, some don't. From what I understand in the presence of tartrate reagent seems to be more stable, otherwise it has to prepared fresh. In both cases it works.

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[chemisttree]

Tartrate chelates the copper and helps prevent the copper hydroxide/copper oxide from forming. Copper hydroxide forms pretty fast when you add copper sulfate and sodium hydroxide together.

I've read that citrate can be used as well.

 

[jkost]

sodium potassium tartrate is not available... i solved the problem by keeping both chemicals copper sulfate and sodium hydroxide into separate bottles and only mix them together when I'm trying a protein test...

you said something about citrate, what do you mean? can i repalce sodium potassium tartrate with something else so i can keep the biuret reagent in one bottle and not it two??

 

[chemisttree]

Yes, use sodium citrate (tribasic) dihydrate. The citrate should be used at a rate of about 10:1 (grams:grams) relative to copper sulfate.

 

[jkost]

also hard to find...

from what i understand it needs an alkalizing agent, is there something else i can use which is readily available? unless if i can react citric acid possibly from lemons? with sodium hydroxide.. can i do that?

 

[Borek]

Citrate - just like tartrate - is there to complex copper. You may take citric acid (should be not difficult to find - I remember it being sold in groceries) and mix it with hydroxide - that will give you citrate.

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[jkost]

indeed...citric acid is very common it can be used instead of lemon so you can find it anywhere...

could you please tell me how i should mix it with sodium hydroxide?

 

[Borek]

Where is the problem? In water, just follow neutralization stoichiometry (citric acid is triprotic). Small excess of base won't hurt, as you want final solution to be basic.

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[chemisttree]

also hard to find...

from what i understand it needs an alkalizing agent, is there something else i can use which is readily available? unless if i can react citric acid possibly from lemons? with sodium hydroxide.. can i do that?

Tartrate is not hard to find. Look in your spice isle in your local grocer. Use "Cream of Tartar". Its potassium hydrogen tartrate. Pure citrate is much more difficult to find unadulterated.

 

[jkost]

chemisttree maybe it's funny but i wasn't aware that i can find citric acid and cream of tartar so easily... though in the past my family used citric acid in the kitchen... i had totally forgotten about it!

now i got the citric acid...but can you tell me how can i use the cream of tartar? so i can try both ways?

 

[Borek]

Creat of tartar is potassium HYDROGE tartrate - that means it still has one acidic proton to neutralize. That's not different (qualitatively) from neutralization of citrate, just molar ratio must be different.

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[jkost]

means i can use sodium hydroxide for both receipes? looks like NaOH goes with everything..

 

[chemisttree]

From http://faculty.mansfield.edu/bganong/biochemistry/reagents.htm"

Biuret Reagent: Add, with stirring, 300 mL of 10% (w/v) NaOH to 500 mL of a solution containing 0.3% copper sulfate pentahydrate and 1.2% sodium potassium tartrate, then dilute to one liter. The reagent is stable for a few months but not a year. Adding one gram of potassium iodide per liter and storing in the dark makes it stable indefinitely.
The reagent can be used either qualitatively or quantitatively. In a typical reaction, one volume of sample is mixed with two to five volumes of reagent; the optimal ratio depends on the maximum protein concentrations you want to be able to resolve. The presence of protein gives a violet color with maximum absorbance around 550-555 nm; we typically read absorbances at 540 nm.

Notice that the amount of NaOH dwarfs the amount of tartrate! Just substitute cream of tartar and get on with it!

 

[jkost]

chemisttree and Borek great guys both of you! thanks... i kinda learned
interesting things since i joined the forums!

now i was wondering can i also make the potassium iodide easily? hehehhe...