Carbohydrate tests Flashcards
(16 cards)
Fehling’s test
10cm3 Fehlings A + 10cm3 Fehlings B = Fehlings Mixture.
1ml sugar solution + 1 ml Fehlings mixture + heat
Brick red precipitate
Positive for all reducing sugar (a sugar is reducing only if it has a free anomeric carbon) - aldehyde groups and fructose.
Mono and Disaccharides
5 drops of sugar solution + 1ml of Benedict solution + heat
tests all reducing sugars - disaccharides (lactose, maltose)
Brick red precipitate
List non reducing sugars
Sucrose ( only common one)
Polysaccharides (until they have been hydrolysed to monosaccharides)
What forms Molisch’s reagent?
1% alpha naphtol in ethanol
Sugar solution + Molisch’s reagent + conc H2SO4
Non nitrogenous carbohydrates
Pink/Purple colour at interface
Barfoed’s test
For reducing monosaccharides Red precipitate (reddish brown)
Fearons test
For reducing disaccharides (excluding sucrose)
Yellow to red colour change
Foulger’s test
For ketohexoses especially fructose
Blue colour
Seliwanoffs test
Ketohexoses/6 carbon monosaccharides (fructose)
Deep red colour with or without brown ppt
Tauber’s test
Pentoses (ribose, arabinose, xylose)
Cherry red colour
Bial’s test
Pentoses (especially ribose)
Greenish blue
Iodine test
Polysaccharides
Blue black
Rubner’s test
Disaccharides (maltose, lactose)
Dense white ppt for lactose
Slight white ppt for maltose
Raybin’s test
Sucrose
Initial green colour changing to blue in 10 mins
Anthrone test
All carbs
Blue green colour
List the general tests for carbohydrates
Fehlings
Benedict’s
Molisch’s
