In this test, the presence of peptides results in the creation of pale purple coloured (or mauve coloured) coordination complexes of the copper(II) ion (when the solution is suitably alkaline) (when the solution is sufficiently alkaline). An illustration detailing a positive biuret test and the characteristic pale purple coloration that signifies it is presented below.
The Biuret test works by measuring the change in color of the reagent in the presence of protein. Peptide bonds in the protein coordinate with the copper ions in the reagent, causing a change in color from pale blue to deep purple.
The Biuret test is simple, inexpensive, and can be used to detect proteins in a wide range of samples. It is also a common test used in many laboratory settings.
The Biuret test is not specific for proteins and can give a positive reaction for other compounds that have peptide bonds such as some dipeptides and tripeptides, and even some non-peptide compounds such as urea.
The Biuret test can be used to detect proteins in a wide range of samples, including blood, urine, food, and agricultural products.
The accuracy of the Biuret test can vary depending on the sample type and the specific application. It is usually recommended to use other methods such as SDS-PAGE to confirm the presence and the identity of proteins in the samples.
The Biuret reagent should be stored in a cool, dark place to prevent contamination or decomposition.
The samples should be homogenized and diluted properly to obtain accurate results.
Proper handling of reagents, sample preparation, use of clean glassware, accurate measurement of reagents, timing, lighting conditions, and safety measures should be taken in order to obtain accurate and reliable results.