Polarimeter

notes

1. QC II POST LAB POLARIMETER

2. AS AN INSTRUMENT is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.

3. PARTS OF

4. Polarimeter tube

5. Operation Panel ZERO SET ROTATE R L TEMP

6. PRINCIPLE

7. RESULTS IN POLARIMETER When the left semicircular field is the brighter (left handed rotating sample) continuously press the left handed ROTATE switch and the translucent semi-circular fields gradually change as below:

8. RESULTS IN POLARIMETER When the right semicircular field is the brighter (right handed rotating sample) continuously press the right handed ROTATE switch and the translucent semi-circular fields gradually change as below:

9. TYPES OF POLARIMETER Laurent's half-shade polarimeter Biquartz polarimeter Lippich polarimeter Quartz-Wedge polarimeter Manual Semi-automatic Fully automatic

10. CALCULATION (a) t = 100a D l X c = a l X c (g/ mL )

11. PROBLEM SOLVING G DATA conc of sample - 300 grams Length of the observation tube - 1 dm Temperature - 25C Wavelength of measuring light used- 589nm Reading of the rotation of the sample- 113 Specific rotation of sample - ?

12. PROBLEM SOLVING G 2. DATA conc of sample - ? Length of the observation tube - 10 cm Temperature - 25C Wavelength of measuring light used- 589nm Reading of the rotation of the sample- 125 Specific rotation of sample - 145

13. PROBLEM SOLVING G 3. DATA Conc of sample - 10 g Length of the observation tube - 10 cm Temperature - 25C Wavelength of measuring light used- 589nm Reading of the rotation of the sample- ? Specific rotation of sample - 110

14. SOURCE OF ERRORS The angle of rotation of an optically active substance can be affected by: Concentration of the sample Wavelength of light passing through the sample (generally, angle of rotation and wavelength tend to be inversely proportional) Temperature of the sample (generally the two are directly proportional) Length of the sample cell (input by the user into most automatic polarimeters to ensure better accuracy) Filling conditions (bubbles, temperature and concentration gradients) Most modern polarimeters have methods for compensating or/and controlling these errors

15. APPLICATION Chemical industry Many chemicals exhibit a specific rotation as a unique property (an intensive property like refractive index or Specific gravity) which can be used to distinguish it. Polarimeters can identify unknown samples based on this if other variables such as concentration and length of sample cell length are controlled or at least known. This is used in the chemical industry. By the same token, if the specific rotation of a sample is already known, then the concentration and/or purity of a solution containing it can be calculated. Most automatic polarimeters make this calculation automatically, given input on variables from the user

16. APPLICATION Food, beverage and pharmaceutical industries Concentration and purity measurements are especially important to determine product or ingredient quality in the food & beverage and pharmaceutical industries. Samples that display specific rotations that can be calculated for purity with a polarimeter include: Steroids Diuretics Antibiotics Narcotics Vitamins Analgesics Amino acids Essential oils Polymers Starches are the most abundant substances in nature and used in various sectors of the food and pharmaceutical industry as well as the building sector. Polarimetric quality control of starch therefore is important in various industries. Sugars

17. SEATWORK 1.A sample of pure 2-butanol was placed in a 10cm polarimeter tube. Using the D-line of a sodium lamp, the observed rotation at 20C was a= +104 ° . The conc of the compound is 0.805 g/ mL. What is the specific rotation of 2-butanol?

18. ANSWER TO SEATWORK T/D = A/ Lx C T/D = ? A = 104 ° l = 10 cm or 1 dm c = 0.805 g/ mL = 104 / 1 dm X 0.805 g/ mL = + 129 °

19. SEATWORK: 2. Calculate the observed rotation of a solution of 5.245 g of 1-ammonium-1-phenylethane diluted to a volume of 100 mL w/ a methanol at 20C using the D-line of a sodium lamp and a 1 dm tube. Specific rotation of this material=(-30 ° ) Sample concentration is 5.245 g in 100mL

20. ANSWER TO SEATWORK 2. T/D = A/ Lx C A = ? T/D = -3O L = 1.00 dm C = 5.245 g in 100 mL -30 = X100 1 X 5.245 g/ 100 mL -30 (5.245) = x100 100 x =-157.35 °

21. SEATWORK: 3. Calculate the specific rotation of 2,3-tartaric acid based on the ff observation: A 0.856 g sample of pure acid was diluted to 10 mL w/ water and observed in a 1.00 dm polarimeter tube. The observed rotation using the 589 nm line of a sodium lamp at 20C was a=+1.06 ° .

22. ANSWER TO SEATWORK 3. T/D = A/ Lx C T/D = ? A = +1.06 L = 1 dm C = 0.856 g in 10 mL T/D = 1.06/ 1 X 0.856 g/ 10mL = 1.06/ 0.0856 = 12.38 °