Exp 4.2: NA Tests

Question 1

Test for phosphates:
purpose
reagents
positive result
principle

Answer 1

purpose: detects phosphate ions
reagents: conc. HNO3 & (NH4)2MoO4
positive result: yellow crystallin precipitate
principle: precipitation of (NH4)3PO4 ⋅ 12MoO4 [ammonium phosphate dodecamolybdate]

Question 2

diphenylamine or dische test:
purpose
reagents
positive result
principle

Answer 2

purpose: detects deoxyribose sugars of purine nucleotides (generally 2’-deoxypentoses)
reagents: diphenylamine in conc. H2SO4; glacial acetic acid
positive result: blue complex
principle: dehydration and complexation

Question 3

Bial’s Orcinol test:
purpose
reagents
positive result
principle

Answer 3

purpose: detects presence of ribose (specific for pentoses); for estimation of RNA)
reagents: orcinol in HCl with FeCl3
positive result: blue-green coloration
principle: dehydration and condensation

Question 4

Murexide test:
purpose
reagents
positive result
principle

Answer 4

purpose: detects presence of purines and its derivatives (adenine & guanine)
reagents: conc. HNO3 & (NH4)OH/KOH
positive result: purplish red solution
principle: oxidation, condensation, and neutralization

Question 5

Wheeler-Johnson test:
purpose
reagents
positive result
principle

Answer 5

purpose: detects pyrimidines: 1,3-diazine and its derivatives (for uracil & cytosine, negative for thymine)
reagents: standard Br2-H2O solution & Ba (OH)2
positive result: purple color
principle: formation of dialuric acid and neutralization