When a sample give negative result for ninhydrin and biuret test but the same sample give positive result for xanthoprotic testwhy?

Why does use sulphur powder for hays's testwhy only get sulphur powder?

Sulfur powder is used in the Hays test because it is a reagent that reacts with certain compounds to produce a characteristic color change. The Hays test is used to detect the presence of reducing sugars, which are sugars that are able to reduce certain compounds and can be oxidized to form an aldehyde or a ketone. When sulfur powder is added to a solution containing a reducing sugar, the sulfur powder reacts with the sugar to form a compound called a sulphone. The sulphone has a distinctive yellow color, which indicates the presence of reducing sugar. Sulfur powder is chosen as the reagent for the Hays test because it is inexpensive and readily available. It is also relatively stable and easy to use, making it a convenient choice for this type of test. The Hays test is a simple and rapid method for detecting the presence of reducing sugars in a solution. It is commonly used in the food industry, particularly in the testing of fruit juices, syrups, and other sweetened products. To perform the Hays test, a small amount of sulfur powder is added to a sample of the solution being tested. The mixture is then heated, and the presence of a reducing sugar is indicated by the formation of a yellow sulphone compound. The Hays test is a qualitative test, meaning that it does not provide a precise measure of the amount of reducing sugar present in the sample. Instead, it simply indicates the presence or absence of reducing sugars. Other methods, such as the Benedict's test or the Fehling's test, can be used to quantify the amount of reducing sugar present in a sample. These tests are more complex and require additional reagents, but they provide a more accurate measurement of the sugar concentration.