refractive index

Refraction main principle

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

Refractometry

Method of measuring the refractive index of substances

Refractive index

A basic physical property of pharmaceutical materials.

Refractive index

the ratio of the velocity of light in air to its velocity in that material under like conditions

Refractive index of liquid pharmaceuticals and liquid raw materials is useful for:

-Identifying a pure substance
-Establishing the purity of some substances
-Determining the concentrations of some solutions, such as alcohol solutions or sugar solutions (e.g. percentage of sugar in syrup)
Determining the uniformity of final compounded preparations

refractive index formula

c/v (velocity of light in vacuum/ velocity of light in a medium)

refractive index is defined as

- as the ratio of the velocity of light in a vacuum (c) to the velocity of light in a medium (v)
-ratio of the velocity of light in air to its velocity in that material under like conditions

refractive index formula

sin i / sin r= c/v

Samples with different refractive index will produce

different angles of refraction

The higher the refractive index,

the higher the optical density and slower is the speed of light.

that light travels proportionately slower in

water than in a vacuum.

The Value for Refractive Index are for the D line Sodium

Double at 589.0 nm and 589.6 nm

The Refractive Index of a material is DEPENDENT ON:

-temp
-wavelength of light

Tips:

-Refer to "temperature control" table for best results.
-Do not use the ff solvents that are known to attack the prism: Ether, Chromic acid, Strong mineral acids, Strong basic solutions
-If the sample is too viscous, use a wooden or plastic spatula to completely fill the space between prisms.

Molar refraction (Rm)

is related to both the refractive index and the molecular properties of a compound being tested.

Refractometer

Is the instrument used in the determination of the refractive index

Abbe Refractometer

-The sample is held between the illuminating prism and the refracting prism.
-A light source is allowed through the illuminating prism.
-The detector is placed behind the refracting prism.

C—(single)

2.418

—C— (double)

1.733

—C☰ (triple)

2.398

Phenyl (C6H5)

25.463

H

1.100

O (C=O)

2.211

O (O—H)

1.525

O (ether, ester, C—O)

1.643

Cl

5.967

Br

8.865

L

13.900

Refraction

Bending of light rays as they pass obliquely from one medium into another of different optical density

Why refraction happens?

-As light enters a denser substance, the waves interact with the atoms in the substance modifying the light waves by absorbing energy, resulting to reduction of the speed and shortening the wavelength
-The waves slows down produces a bending of wave

The following are different refractometers:

Traditional handheld refractometer
Digital hand held refractometer
Abbe refractometer
Inline process refractometer

FACTORS AFFECTING THE REFRACTIVE INDEX

temp
viscosity
wavelength

Temperature

It is inversely proportional to the refractive index

Viscosity

It is inversely proportional to the refractive index

Wavelength

The sodium D-line at 595 nm is the appropriate wavelength for the determination of the refractive index

A higher temperature means the liquid becomes less dense and less viscous,

causing light to travel faster in the medium

APPLICATIONS
Refractive index of liquid pharmaceuticals and liquid raw materials is useful for:

1. Identifying a pure substance
2. Establishing the purity of some substances
3. Determining the concentrations of some solutions such as alcohol solutions or sugar solutions
(E.g: percentage of sugar in syrup)
4. Determining the uniformity of final compounded preparations