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Biochemistry Laboratory > QUALITATIVE TESTS FOR CARBOHYDRATES > Flashcards

QUALITATIVE TESTS FOR CARBOHYDRATES Flashcards

1
Q

BENEDICT’S TEST, BARFOED’S TEST, SELIWANOFF’S TEST, BIAL’S ORCINOL TEST

A

QUALITATIVE TESTS FOR
CARBOHYDRATES

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2
Q

are polyhydroxyaldehydes (aldoses) & polyhyroxyketones(ketoses)
General Formula: (CH20)n

A

Carbohydrates

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3
Q

based on the number of monosaccharide units they contain

A

Classification

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4
Q

one sugar molecule. Ex. Glucose, Fructose, Galactose

A

Monosaccharides

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5
Q

two sugar molecule. Ex. Sucrose, Lactose, Maltose

A

Disaccharides

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6
Q

two to ten sugar mol ex. Raffinose, Stachynose

A

Oligosaccharides

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7
Q

ten or more sugar molecules ex. Starch, glycogen, cellulose

A

Polysaccharides

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8
Q

simplest sugar and cannot be hydrolyzed further.
Classification is by the number of carbon atoms they contain

A

Monosaccharide

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9
Q
  • Pentoses: five carbon atoms
  • Aldopentoses: ribose & Xylose
  • Hexoses: six carbon atoms
  • Aldohexoses: glucose, galactose
  • Ketohexose: fructose
    On hydrolysis, disaccharides yield two monosaccharide units.
A

Classification is by the number of carbon atoms they contain

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10
Q

Dehydrating acids (2-step analysis)

Copper (Il) ions containing solutions

A

Two general classes of carbohydrate test reagents based on the type of reaction involved

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11
Q
  • Converts pentoses into furfural and hexoses into 5-hydroxymethylfurfural which then reacts with phenolic compounds
  • Production of highly colored products
  • Molisch’s, Anthrone, Bial’s & Seliwanoff’s tests
A

Dehydrating acids (2-step analysis)

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12
Q
  • CHO reduces copper (Il) ions into copper (1) oxide
  • Reducing sugars include aldoses containing either a free aldehyde group or a cyclic hemiacetal
A

Copper (Il) ions containing solutions

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13
Q
  • To determine the presence or absence of reducing sugar in the solution.
  • All monosaccharides are reducing sugars
  • A reducing sugar has a free aldehyde group or a free ketone group
A

Benedict’s Test

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14
Q

Principle of the Test
Benedict’s reagent contains copper (Il) ions in an alkaline solution with sodium citrate to keep the cupric ions in solution. Test is performed by heating the reducing sugar solution with Benedict’s reagent.
Alkaline condition of this test causes isomeric transformation of ketoses to aldoses resulting in the reduction of blue cupric ion to cuprous oxide

A

Benedict’s Test

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15
Q
  1. presence of reducing sugar with either ketone or aldehyde, positive color brick-red or brick red precipitate caused by reducing property of simple sugar
    Alkaline reagent
    Copper sulfate in benedict solutions are reduced to copper ions
    Cupric to cuprous ions
    Composition: Sodium carbonate 10g, sodium citrate 17.3g, distilled water 100ml, copper sulfate pentahydrate 1.73 g
    Copper sulfate act as copper 2+ (Cu ^2+) ions
    Sodium carbonate as an alkaline medium
    Sodium citrate: forms complexes to Cu 2+ ions
    Test tube
    Test tube holder
    Pippete
    Urine sample
    Burner
    Beaker
    2 ml of sample urine + 3mL of benedicts reagent mix heat
    Brick red large amount of reducing sugar, >2 percent
    Red - brick red
    Blue indicate negative, 0 percent
    Green has trace of reducing sugar, variable color, 0.5-1 percent
    Yellow, is low 1.1-5 percent or orange, 1.5 - 2 percent moderate amount of reducing sugar
A

Benedict’s test

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16
Q
  1. check if its monosaccharide or disaccharide
    Copper ions to copper oxide
    Reducing sugar: aldehyde or ketones
    Monosaccharides- reacts fast, all are reducing sugars ex. Lactose and maltose non reducing sucrose
    Disaccharide - reacts slowly
    Reagent: copper sulfate, acetic acid: provide acidic condition that would decrease pH
    Monosaccharide + barfoed results to brick red or red or brown precipitate within 5 mins
    Disaccharide + barfoed appear to precipitate within 10 mins brick red
    What’s positive reaction for barfoed brick red or brown precipitate
    4 test tube 1 percent per tube of glucose, lactose, fructose, negative control or distilled water lagay barfoed 2ml
    Drum test tube in water butt or beaker
A

Barfoed’s test

17
Q

distinguish if ketose or aldose
Ketose - contain ketone group
Ketose from aldose sugars
Aldose example glyceraldehyde, erythrose, ribose, arabinose, xylose, glucose, mannose, galactose
Ketose ex. dihydroxyacetone, erythrulose, ribulose, fructose, and sedoheptulose
Rapid state of hydration than aldose
Seliwanoffs reagent - orcinal and hydrochloric acid
Aldose - light pink - negative
Ketose - cherry red - positive

A

Seliwanoff’s test

18
Q

check if pentose or hexose
Bial’s orcinal
Ribose and xylose - pentose
Blue - Green Positive color
Any color besides green negative
5 percent fructose, ribose, sucrose, glucose
2 ml bials reagent

A

Bial’s Orcinol test

19
Q
  1. Benedict’s reagent
  2. Barfoed’s reagent
  3. Seliwanoff’s reagent
  4. Orcinol reagent
  5. Carbohydrate solutions
(0.1 M glucose, fructose, xylose, galactose, lactose, sucrose and 1% starch)
  6. Beaker
  7. Alcohol lamp
  8. Hot plate
  9. Distilled Water
A

Benedict’s Test, Barfoed’s,
Seliwanoff’s and Bial’s Orcinol tests
REAGENTS & MATERIALS

20
Q

Test Objective
* Barfoed’s test is a chemical test used to detect the presence of reducing monosaccharides.
* To distinguish reducing monosaccharides from disaccharides

A

Barfoed’s test

21
Q

Principle of the Test
The Barfoed reagent is made up of copper acetate (cupric ions) in a dilute solution of acetic acid. (acidic medium)
Reducing Monosaccharides are strong reducing agent: React within 3 minutes
Reducing Disaccharides have to first to get hydrolyzed in the acidic solution and then react with the reagent: React in about >3 minutes

A

Barfoed’s test

22
Q

Interpretation of Result
Positive Result: Brick red precipitate at the bottom of the tube.
Monosaccharide: ≤ 3 minutes
Disaccharides: >3 minutes
The difference in the time of appearance of precipitate thus helps distinguish reducing monosaccharides from reducing disaccharides.

A

Barfoed’s test

23
Q

Test Objective
* To detect the presence of ketohexoses in a given sample.
* To distinguish ketoses from aldoses.

A

Sellwanoff’s Test

24
Q

An aldose contains one aldehyde group per molecule.
A ketose contains one ketone group per molecule
In Seliwanoff’s test, Aldoses react slowly and produce a light pink colour.
In Seliwanoff’s test, Ketoses react with resorcinol to give a deep cherry-red colour.

A

ALDOSE VS KETOSE

25
Q

Principle of the Test
* The reagent of this test consists of resorcinol in 6M HCI.
* The acid hydrolysis of polysaccharides and oligosaccharides yields simpler sugars.
* Ketoses are more rapidly dehydrated than aldoses.
* Ketoses undergo dehydration in the presence of concentrated acid to yield hydroxymethyl furfural that condense with resorcinol

A

Seliwanoff’s Test

26
Q

Interpretation of Result
* Ketose reacts to produce a deep cherry red color
* Aldoses may react slightly to produce a faint pink to cherry red color if the test is prolonged.
* The product and reaction time of the oxidation reaction helps to distinguish between carbohydrates.
* Sucrose and inulin also give a positive result for this test as these are hydrolyzed by acid to give tructose.

A

Seliwanoff’s test

27
Q

Test Objective
In chemistry, a pentose is a monosaccharide (simple sugar with five carbon atoms. The chemical formula of all pentoses is C5H100.
* To detect the presence of carbohydrates.
* To distinguish the pentoses and pentosans from other derivatives of carbohydrates like the hexoses.

A

Bial’s Orcinol Test

28
Q
  • This test is based on the principle that under hydrolysis pentosans are hydrolyzed into pentoses.
  • Further, pentoses are dehydrated to yield furfural, which in turn condense with orcinol to form a blue-green precipitate. In the presence of hexoses, hydroxyfurfural is formed instead of furfural which upon condensation with orcinol forms a muddy brown colored precipitate
  • The intensity of the precipitation is directly proportional to the concentration of the pentoses in the sample.
  • The intensity of the color developed depends on the concentration of HCl, ferric chloride, orcinol, and the duration of boiling.
A

Bial’s Orcinol Test

29
Q

Interpretation of Result
• The presence of a blue-green complex indicates the presence of pentoses in the sample.

A

Bial’s Orcinol Test

Biochemistry Laboratory (4 decks)

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