Polarimetric Analysis of Carbohydrates
Name of Student
Date of Submission
Polarimetric Analysis of Carbohydrates
Results
1.
Deionized Water Readings
1 -10
2 -10
3 -10
4 -10
5 -10
Average DI water reading = 10
Corrected values for glucose concentration DI Rotation Observed Rotation Concentration
1 -10 3.35 13.35 0.1267
2 -10 3.30 13.30 0.1262
3 -10 3.35 13.35 0.1267
4 -10 3.45 13.45 0.1276
5 -10 3.35 13.35 0.1267
Formula for Specific Rotation
[a]=a (observed) /c * l
Where;
A (observed) = Observed rotation in degrees
[a] = Specific rotation in degrees
C = Concentration in g/ml
L = Path length in dm
To find concentration, the equation changes to
C = a (observed)/ l * [a]
=13.35 / 2 * 52.7
0.1267
C = a (observed)/l * [a]
=13.30/2 * 52.7
0.1262
C = a (observed)/l*[a]
=13.45/2 *52.7
0.1276
2. Identification of an Unknown
Carbohydrate Unknown D Readings
observed Rotation
1 -8.85 18.85
2 -8.90 18.90
3 -8.95 18.95
4 -8.85 18.85
5 -8.90 18.90
Mass of solute= 4.9809
Total volume = 50.015
Concentration = mass/volume
Concentration = 4.9809/50.015
Concentration = 0.09959
Specific Rotation [a] = a (observed)/(c * l)
[a] = 18.85 /(0.09959 * 2)
= 18.85/ 0.1992
=94.63
The unknown carbohydrate has a specific rotation of 94.63. The nearest carbohydrate with the specific rotation is L-arabinose with a specific rotation of 104.5
Error = (Actual specific Rotation –Calculated specific Rotation)/ Actual specific rotation
Error = (104.5-94.63)/104.5
Error = 0.0944
%Error = Error * 100
%Error = 0.0944 * 100
% Error = 9.44%
Readings Observed Rotation
0 minute Solutions Readings
AVERAGE = 3.56 6.55 3.45
6.45 3.55
6.40 3.60
6.45 3.55
6.35 3.65
15 Minute Solution Reading AVERAGE= 5.86 4.10 5.9
4.15 5.85
4.20 5.8
4.10 5.9
4.15 5.85
30 minute Solution Reading AVERAGE= 9.57 0.00 10
0.45 9.55
0.70 9.3
0.60 9.5
0.50 9.50
-3.10 13.10
-3.05 13.05
-3.10 13.10
-3.10 13.10
-3.00 13.00
-3.70 13.70
-3.70 13.70
-3.70 13.70
-3.90 13.90
-3.75 13.75
AVERAGE Observed Rotation 60 minutes = 13.75
AVERAGE Observed Rotation 45 minutes = 13.11
Time in minutes Average Observed Rotation
0 3.56
15 5.86
30 9.57
45 13.11
60 13.75
The graph above is graph of the average observed rotation as a function of hydrolysis time. It is a straight line graph which cuts the Y-axis at the point 3.16
10. Sucrose + water = Glucose + Fructose
X = (6.65(d) – A (observed))/0.872(d)
But d = 2 dm
For the 5 observed rotation values
O minutes observed rotation = 3.56
X = {(6.65 * 2) – 3.56}/0.872 *2
X = 5.59g
15 minutes observed rotation = 5.86
X = {(6.65*2) – 5.86}/1.7441
X= 4.25g
30 minutes observed rotation = 9.57
X = {(6.65*2) – 9.57}/1.744
X = 2.13g
45 minutes observed rotation = 13.11
X = {(6.65*2)-13.11}/1.744
X = 0.11g
60 minutes observed rotation = 13.75
X= {(6.65*2)-13.75}/1.744
X=-0.24g which is approximately zero.
11. Percentage hydrolysis
%hydrolysis = X (100)/10
%Hydrolysis=X (10)
For O minutes = 5.59 * 10
=55.9%
For 15 minutes = 4.25* 10
=42.5%
For 30 minutes= 2.13*10
=21.3%
For 45 minutes= 0.11*10
1.1%
For 60 minutes = 0*100
0%
Discussion
Polarimetry is an effective tool used for both qualitative and quantitative analysis. Due to the similarity in the physical properties of most enantiomers, polarimetry is the best method since it measures a quantity called optical activity. Examples of physical properties which are similar are; melting point, boiling point and the refractive index. In measuring optical activity, the sample rotates the plane of polarization of a polarized light beam through. Because plane polarized light is affected differently by enantiomers, it becomes a very useful tool to quantify the amount of an enantiomer or enantiomers present in a sample. Hence, polarimetry is an effective tool for both the qualitative and quantitative aspects. In addition to that, it can be effectively used to measure optical purity. Today it is used widely in quality control and process operations especially in the pharmaceutical industry, food and industrial chemistry. The optical purity of a product is determined by measuring the specific rotation of compounds like the amino acids and antibiotics (Pomeranz and Meloan, 1994).
The graph of the catalyzed hydrolysis of sucrose is non-linear. This is because the resulting mixture between glucose and fructose is slightly levorotatory. Levorotatory glucose has a greater, molar rotation than dextrorotatory glucose. It is not straight since the glucose is used up while the glucose fructose mixture is formed. Consequently, the angle of rotation becomes significantly smaller and smaller. Finally the light will be rotated to the left. Since the reaction is in pure water, it proceeds at a very slow pace (Edye and Richards, 1991).
References
Edye, L. A., Meehan, G. V., & Richards, G. N. (1991). Platinum catalysed oxidation of sucrose.
Pomeranz, Y., & Meloan, C. E. (1994). Refractometry and polarimetry. In Food analysis (pp. 430-448). Springer US.
