Biuret Test for Proteins and Emulsion Test for Lipids

Topics: Protein, Solvent, Acid Pages: 2 (514 words) Published: May 20, 2013
molecules consisting of one or more chains of amino acids.Proteins are complex molecules that react differently to many compounds but are also fragile and cannot withstand high temperatures or strong acids and bases without degrading. The Biuret Method, or biuret test, is used to detect the presence of peptide bonds. It has this name because it reacts positively to the biuret molecule's peptide bonds. Correctly evaluating the number of peptide bonds is a step towards determining the protein content of the sample. In the Biuret Test, copper ions form a violet-colored complex when in the presence of peptide bonds in an alkaline solution. The intensity of the violet color is directly proportional to the protein concentration, according to the Beer-Lambert law. For this test, a specific reagent is needed, in this case, the biuret reagent. The alkaline solution is made of potassium hydroxide, a strong base. A compound of hydrated copper sulfate and potassium sodium tartrate is dissolved in this solution, turning blue. In the presence of proteins, the reagent turns violet, but turns from blue to pink in the presence of short-chain polypeptides, or basic amino acids. This dual sensitivity is useful to determine if the sample has complex proteins or only the simpler amino acids. On higher concentrations and when there is only need to confirm the presence of proteins, a simple visual check for color change is enough.

The lipids are a large and diverse group of naturally occurring organic compounds that are related by their solubility in nonpolar organic solvents The emulsion test is a method to determine the presence of lipids using wet chemistry. The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water. Since lipids do not dissolve in water, when the ethanol is diluted, it...
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