Seliwanoff and xanthoproteic tests are used for the identification of ketoses and proteins respectively.
Seliwanoff test It is a chemical test which distingusihes between aldose sugars (e.g. glucose and maltose) and ketose sugars (e.g., fructose and sucrose). The test is based on the principle that, when heated with acid, ketoses are more readily dehydrated than aldoses. The reagents used in the test consist of conc.
HCl and resorcinol.
Ketoses
| ‌ Conc. ‌HCl |
| ───────▶ |
Deep cherry red colour
Aldoses Resorcinol
| ‌ Conc. ‌HCl,Resorcinol |
| ─────────────▶ |
Faint pink colour
For ketoses, a deep cherry red colour is formed rapidly indicating a positive test. Xanthoproteic test It is qualitative test to detect the presence of protein soluble in a solution using
HNO3.
In this test, solution of protein is first heated with conc.
HNO3 and then the mixture is neutralised by
40%NaOH solution. If the colour changes from yellow to orange, this confirms presence of a protein.
Protein solution
| ‌ (i) Conc. ‌HNO3∕∆ |
| ──────────▶ |
| (ii)40%NaOH |
Yellow colouration which finally changes into orange colour.