How should I do the biuret test?
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. Hope this helps.
