BCH 2720 IBM
Expt.1:
Qualitative Tests for
Carbohydrates and Amino Acids
1a: Carbohydrates
Characterization
• Molisch’s Test : carbohydrate
• Barfoed’s Test : Monosaccharides and
Oligosaccharides
• Seliwanoff Test : Differentiation of Ketose
from Aldose
• Iodine Test : Cellulose, Starch, Dextrin
Experiment 1
Qualitative Tests for Carbohydrates
I. Principle
1. Molisch’s Test
- test for carbohydrates
Pentose/
Hexose
conc.H2SO4
- H2O
a-naphthol
Furfural
5-hydroxymethyl furfural
(Purple complex)
2. Barfoed’s Test
- test for reducing sugars
- test for distinguishing monosaccharides
and disaccharides
Slightly acidic
Reducing sugar + 2Cu2+
2Cu+ + oxidized sugar
Cu2O
(brick red ppt)
3. Seliwanoff Test
- test for distinguishing ketose from aldose
Ketohexose
conc. HCl
dehydration
4. Iodine Test
- test for starch
Starch + I2
5-hydromethyl
furfural
resorcinol
starch - I2 complex (deep blue)
red complex
Barfoed's Test
RCHO + 2Cu2+ + 2H2O -----> RCOOH + Cu2O + 4H+
Barfoed's reagent reacts with monosaccharides
to produce cuprous oxide at a faster rate than
disaccharides do
Monosaccharide &
Disaccharides
Monosaccharide
• Glucose
• Fructose
Disaccharides
• Maltose
• Lactose
• Sucrose
Ketone & Adehyde
Polysaccharide
• Starch
• Glycogen
• Cellulose
Molisch’s Test
• Test for carbohydrate materials
• Using 2 ml of test solution in a test
tube, add 50 l of the a 1-naphthol,
mix and then allow 1 ml of conc.
Sulphuric acid to flow down the side
of the inclined tube to layer under the
mixture. Note the colour at the
junction.
Barfoed’s Test
• Test for Monosaccharides and
Oligosaccharides
• Using 0.5 ml of test solution, mix with
2.5 ml of Barfoed’s solution in a test
tube and boil for 15 minutes. Note
the time of first sign of precipitate
appears. After 15 minutes, cool it
down and observe the amount of
precipitate in each tube.
Seliwanoff Test
• Test for Differentiation of Ketose from
Aldose
• Add 0.5 ml of the test solution to 2.5
ml of the Seliwanoff’s reagent. Place
the tubes in boiling water and note
the results and continue heating,
observe the colour change at 1
minute interval for 5 minutes.
Iodine Test
• Test for Cellulose, Starch, Dextrin
• Add 50 l of aqueous iodine solution
to 4 ml test solution. Record the
colours observed. Then heat the
tubes 5 mins, record the effect on the
colours, cool the tube again and note
the effect on the colours.
1b. General Properties of amino
acids
The Ninhydrin Reaction: oxidising
agent
(It reacts with a-amino acids to
produce a purple coloured compound
to measure the amount of a-amino
acid in a sample.)
The Ninhydrin Reaction
• Mix 1 ml of test solution and 50 l of
ninhydrin reagent in a test tube. Boil
for 5 minutes and observe the colour
change. (Tyrosine, Tryptophan &
Proline)
• serial dilution of glycine
Ruhemann’s Pruple
Lab Report
Control is Water
• Date of Experiment : 24 Jan 2006 (Tue)
• Date of Submission: 10 Feb 2006 (Before
5:00p.m.) (Fri)
• Demonstrator in-charge: Edmond
• Room no. : MMW 612A
Lab Report (Con’t)
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Title and Introduction - 0.5 M
Results – 2.5 M
Discussion – 5 M
Conclusion and Recommendation – 1.5 M
Reference – 0.5 M