Refractometry

REFRACTOMETRY

1. REFRACTOMETRY Presented By: G.T.ROOPESH M.PHARM Associate Professor Dept. Of Pharma.Chemistry BCP-ATP CONTACT: 9985111787 EMAIL ID: [email protected]

2. CONTENTS Introduction PRINCIPLE Theory Snell’s Law Refractive Index Factors Affecting Refractive index Temperature, Viscosity & Wavelength Instrumentation (RI Measurement) Types---- Abbe’s Refractometer Application & uses Advantages & Disadvantages REFRACTOMETRY

3. REFRACTOMETRY

4. Refractive Index It is also Commonly Used to:

5. Snell's L aw D escribe the relationship between the angles of incidence and refraction , Snell's law is used to determine the direction of light rays through refractive media with varying indices of refraction. The indices of refraction of the media, labelled n1, n2 and so on, are used to represent the factor by which a light ray's speed decreases when travelling through a refractive medium, such as glass or water, as opposed to its velocity in a vacuum. As light passes the border between media, depending upon the relative refractive indices of the two media, the light will either be refracted to a lesser angle, or a greater one. These angles are measured with respect to the normal line , represented perpendicular to the boundary. In the case of light travelling from air into water, light would be refracted towards the normal line, because the light is slowed down in water; light travelling from water to air would refract away from the normal line.

6. Theory Specific refraction : Denoted By ‘R’ Independent on temp and pressure Lorentz and Lorenz give equation for specific refraction R= n 2 -1/d(n 2 +2) Molar refraction : Denoted By “ Rm ” Specific refraction when multiplied by molecular weight we get molar refraction Rm= M(n 2 -1)/d(n 2 +2) Both are constant at given temp It is characteristic of numerous type of atoms and arrangements found in a molecule Useful in finding the nature of bonding in molecules and dipole movement Molar fraction of solid is total sum of mole fraction of the solvent and the solute along with molar retroactivities R=N1R1+N2R2

7. PRINCIPLE & THEORY The main principle involved in refractometry is the refraction based on the speed of the light that passes in the different mediums. Light enters into the light denser medium to high denser medium at an angle, that is, with bent. The bent in the light ray is known as the refraction. The relation between the refraction of the light between the air and the medium is given by Snell's law: Refractive Index ( n ) = sin i/sin r where n = refractive index; sin i = angle of incidence; sin r = angle of refraction. Samples with different refractive index will produce different angles of refraction. This helps in the assessment of the compounds’ composition and the purity of the compounds.

8. FACTORS AFFECTING THE REFRACTIVE INDEX Temperature Wavelength Viscosity Temperature : It is inversely proportional to the refractive index. Wavelength : The sodium D-line at 5 89 nm (Yellow light) is the appropriate wavelength for the determination of the refractive index . Viscosity: It is inversely proportional to the refractive index.

9. Measurement of RI Two types of instruments REFRACTOMETER Based on measurement of critical ray (angle) or by displacement of image INTERFEROMETER Use interference phenomenon to find out RI

10. INSTRUMENTATION Types of Refractometers OTHER REFRACTOMETERS Traditional Hand held Refractometer Digital Hand held Refractometer Inline Process Refractometer (for continuous liquids through pipes)

11. ABBE’S REFRACTOMETER (Ernst Abbe’s)

12. IMMERSION OR DIPPING REFRACTOMETER

13. IMMERSION OR DIPPING REFRACTOMETER

14. IMMERSION OR DIPPING REFRACTOMETER (Contd.,)

15. 1.RELIEF

16. +ve or – ve R elief A mineral may exhibit positive or negative relief: • +ve relief - index of refraction for the material is greater than the index of the oil. e.g. G arnet 1.76 -ve relief n min < n oil e.g. F luorite 1.433

17. Variation in Relief Strong +ve Moderate to strong +ve Low +ve Moderate to strong -ve Low -ve RI quartz = RI medium RI Mounting Medium = 1.54

18. METHODS TO DETERMINE RI 1.Becke line method 2.Immersion Contrast Method 3. Direct measurement Method 4.Minimum Deviation Method 5. Central i llumination Method

19. 1. Becke Lines To determine whether a mineral has positive or negative relief, the Becke Line method is used. proposed by “ Mittchel ” Becke Lines are a band or rim of light visible along the grain boundary in plane light when the grain mount is slightly out of focus. The Becke line may lie inside or outside the mineral grain depending on how the microscope is focused Becke lines are interpreted to be produced as a result of: the lens effect and/or internal reflection effect.

20. This method involves the determination of RELIEF & Appearance of grindle & the facet edges when immersed in known liquid. 2.Immersion Contrast Method 3. Direct measurement Method Involves the measurement of RI by using a microscope with a vernier scale. By using Table spectrophotometr we can determine the RI . Most Accurate & ideal Method Requires Skill & Ideal Conditions 4.Minimum Deviation Method

21. Central Illumination Method A – When the refractive index of the mineral fragments is greater that that of the immersion medium, a white line (Becke line) forms around the fragments and moves into the fragments as the focus is raised. B – When the refractive index of the fragments is less than that of the immersion medium, the white line moves outward away from the fragments into the immersion medium, as the focus is raised . 5.Central Illumination Method

22. Pulfrich R efractometer

23. Image displacement refractometer Any prism spectrometer is refractometer . Prism shaped vessel containing sample Is used instead of prism of spectroscope, the image of slit will be displaced proportional to RI of sample prism . Refractive index is read from graduated arc provided to a movable telescope arm . Accuracy is about ± 10 -6 in unit of n. Large range of wavelength from UV or IR can be used as source of radiation . Used in gel permeation chromatoghraphy .

24. Principle on which instrument works Fresnel refractometer Deflection refractometer

25. APPLICATIONS & USES

26. Advantages and disadvantages Disadvantages Temperature Corrections (0.00045 per degree Celsius is used) Refractive index not determined in Temperature 20 º or if 20º cooling water is not used to cirucalate in the instrument. Optical Exaltation( Conjugated Double bond) Difference between Observed & Calculated Values of atomic & Structural Constants. Advantages Simple Operation

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