The refractive index or index of refraction of a substance is a measure of the speed of light in that substance. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium.

1. REFRACTIVE INDEX &
SPECIFIC OPTICAL ROTATION
SCHOOL OF PHARMACEUTICAL SCIENCES
RAJIV GANDHI PROUDYOGIKI VISHWAVIDYALYA
BHOPAL (M.P.)
PRESENTED BY
RAVIRAJ S. BAGHEL

2. Refractive index ???
• The refractive index or index of
refraction of a substance is a
measure of the speed of light in
that substance. It is expressed as a
ratio of the speed of light in
vacuum relative to that in the
considered medium.
A simplified, mathematical description of refractive index is:
n = velocity of light in a vacuum / velocity of light in
medium
Hence, the refractive index of water is 1.33, meaning that
light travels 1.33 times as fast in a vacuum than it does in
water.

3. Why Refractive index is Important ?
• The refractive index of a material medium is an important optical
parameter since it exhibits the optical properties of the material.
• Its values are often required to interpret various types of
spectroscopic data. Such as DOAS, ES, RPFTS, IRRS,PWMS.
• It is used to calculate the focusing power of lenses, and the
dispersive power of prisms.
• The refractive index coefficients are important parameters in the
design of a solid state laser.
• The adulteration problem is increasing day by day and hence
simple, automatic and accurate measurement of the refractive
index of materials is of great importance these days.

4. • Refractive Index (RI) Detector is designed for high-performance
liquid chromatography (HPLC) applications. It provides
sensitivity, stability, and reproducibility for the analysis of
components with limited or no UV absorption
• Various methods and techniques for the measurement of
refractive indices of liquids, solids and gases. Sensitive
determination of the refractive indices of certain materials is
very important in many fields of research such as material
analysis and environmental pollution monitoring.
• Refractometric measurements are used for qualitative analysis
for different type of packaging material like glass, plastics,
rubber, silk etc.

5. air
glass
Useful words to describe refraction of light
normal
incident ray
angle of
refraction
angle of
incidence
refracted ray
Refraction is the bending of light when the
light passes from one medium to another
i
r

6. sin i
sin r
• refractive index n =
sin θa
sin θg
ang=
a:air
g: glass
• e.g. for glass,
where
Refractive index

7. i.e. sin i
sin r
= constant
When the ratio of the sin i to sin r is constant.
– This is called Snell’s law.
Laws of refraction
Snell's law states that the ratio of the sines
of the angles of incidence and refraction is
equivalent to the ratio of velocities in the
two media, or equivalent to the opposite
ratio of the indices of refraction.

8. the law is used in ray tracing to compute the angles of incidence
or refraction, and in experimental optics and gemology to find
the refractive index of a material
v = velocity, SI units are m/s
n = refractive index, which is unitless

9. Refractive index and speed of light
distance that light travel in 1 s
distance that light travel in 1 s
vacuum (or air)
3 × 108
m
water (n = 1.33)
2.25 × 108
m
glass (n = 1.5)
2 × 108
m
diamond (n = 2.42)
1.25 × 108
m
diamond (n = 2.42)
1.25 × 108
m

11. Instrumentation
The instrument used to measure refractive index called
Refractometer. There are four main types of refractometers:
•laboratory or Abbe refractometers
•traditional handheld refractometers,
•digital handheld refractometers,
•inline process refractometers.
Most common instrument is the Abbe Refractometer having
following advantages.
1.The index of refraction obtained is actually that for sodium D line.
2.The prisms can be temperature controlled.
3.Only a small sample is required ( a few drop of liquid )

12. • In the Abbe' Refractometer the liquid sample is sandwiched into a
thin layer between an illuminating prism and a refracting prism
(Figure ). The refracting prism is made of a glass with a high
refractive index (e.g., 1.75) and the refractometer is designed to be
used with samples having a refractive index smaller than that of
the refracting prism.

16. Specific Optical ROtatiOn

17. INTRODUCTION
Light in which the (electric and magnetic field) vibrations are confined to
certain directions
• Plane Polarized light.
If the ordinary rays of light is passed through a medium (for ex Nicol prism) ,
the emergent rays has its vibration only one plane. This light having wave
motion in only one plane know as plan of polarized light.

18. • Circularly polarized light: Light is composed of two plane waves of
equal amplitude by differing in phase by 90°.
• Elliptically polarized light: Two plane waves of differing amplitude
are related in phase is other than 90°.

21. • Polarimeters are optical instruments for measuring
the rotation or ‘twisting’ of light. Industrial and
academic laboratories use polarimeters for a variety
of purposes ranging from simple quality control to
fundamental research into complex chemical
structures.

22. • A sample tube containing the test liquid
(solution) is placed between two polarising
elements (polaroid strip or a calcite crystal).
The first element, the polariser, polarises the
light before it passes into the sample. The
second element, the analyser, can be rotated
to counteract any rotation by the sample and
hence locates the resultant angular position of
the light plane and hence the amount of
rotation caused by the sample.

23. Optical Activity
• When certain organic liquids, Solutions (like suger)
or quartz crystal are placed in the path of plane
polarized light, the plane of polarization is rotated.
The property by vertue of which the plane of
polarization of light is rotated called optical activity
and the substance possessing this property are said
to be optical active .
• The substance which are rotate the plane of
polarized light towards the right (Clockwise) are
called DEXTRO-ROTATARY (+) while which rotate
towards left (anticlockwise) called LAEVE-ROTATARY
(-). A mixture of these two varieties in equal
proportion will optically inactive called racemic
mixture

24. The magnitude of rotation depends upon the
following factor
• Nature of substance.
• Length of liquid column (l) through which light
passes.
• Concentration of solution
• Nature of the solvent
• Temp of the solution
• Wavelength of light is used.

25. • The rotatory power of given solution is generally
expressed as specific rotation. It is the number of degree
of rotation of the plane polarized light produced by one
decimeter in length filled with a solution having one
gram of substance per ml. the measurement is carried
out at a temperature t using sodium light.
• The specific rotation can be calculated by following
relation.
α= observation angle of rotation
L= Length in decimeter
C = Grams of substance in 100 ml of solution

26. Application of optical Activity and optical
rotation
• A convenient method for study of optical isomerism, configuration and
conformation of compound
• If the specific rotation of the sample is known, the concentration of
optically active substance in the solution can be calculated. Alternatively .
If the concentration of the material in the sample is known, the specific
rotation can be calculated and used for identification purpose.
• Quantitative methods of analysis by polarimetry are widespread
particularly for plant control in the pharmaceutical industry. The most
extensive application in the sugar industry.
• In other applications, for example R&D, the user may be required to be
fully conversant with the principles and to be in a position to investigate
optical properties of test materials, possibly for the first time.

27. THANK YOU