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  • Published on: 7th September 2019
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SPECTROPHOTOMETER AND ITS COMPONENTS:

DEFINITION OF SPECTROPHOTOMETER:

A spectrophotometer is an apparatus that measures the quantity of light

Immersed by a sample. Spectrophotometer techniques are used to measure

The concentration of solute in solutions by measuring the quantity of light

That is immersed by the solution and cuvette placed in a spectrophotometer.

TECHNIQUES TO MEASURE THE INTENSITY OF LIGHT:

The spectrophotometer technique is to measure the intensity of light which

Works as a function of wavelength. The rays which are not absorbed or

Transmitted such rays can be measured by a detector. A photo diode  

Tube which records and calculates transmittance in terms of conductivity

And display results on a graph and then shown on read out device.

PURPOSE AND USES OF SPECTROPHOTOMETER:

1) MEASURE THE CONCENTRATION OF SOLUTE :

A spectrophotometer theoretically determines the absorbance and

Diffusion of characteristics wavelength of light by a reacting specie

In a solution. Each specie or molecule absorb light at particular wavelength.

In a special pattern because of arrangements of molecules in their

Respective functional group. Such as double bond between carbon atoms.

2) CLASSIFY COMPOUNDS BY DETERMINING MAXIMUM ABSORPTION :

Spectrophotometer is used to classify organic compounds by maximum

And it is for that compounds which have very distinct finger patterns .That

Why absorption curves and peaks are formed.

3) DETERMINATION OF COLOUR WITH IN SPECTRAL RANGE :

The spectrophotometer range from 200nm to 800nm from (200nm to 400nm

There is ultraviolet range) and from (400nm to 800nm there is visible range).

That’s why spectrophotometer is used for color determination which is in visible

Region.

EXAMPLE OF SPECTROPHOTOMETER:

Let suppose we have a light source, a copper sulphate solution and a detector

From which copper sulphate will be distinguished. You will observed that red part of

A spectrum will totally immersed by a copper sulphate solution and blue light

Has been shifted thus copper sulphate absorbs blue light and seems blue in

Color. We will get better sensitivity by leading red line through the solution copper

Sulphate absorbs strongest at the red end of visible spectrum.

 COMPONENTS OF SPECTROPHOTOMETER:

There are five components of spectrophotometer which are as follows:

1) LIGHT SOURCE

2) MONOCHROMATOR

3) CUVETTE

4) DTECTOR

5) READ OUT DEVICE

1) LIGHT SOURCE:

The function of light source is to provide enough light which is appropriate for measurement. The light source characteristically produce a high output of polychromatic light over a wide range Spectrum.

There are types of lamps or light source which are as follows:

1) TUNGSTEN LAMP :

Tungsten halogen lamp is a most communal light source used in

Spectrophotometer the lamp comprise of tungsten filament fenced in

a glass envelope which has wavelength range of 330nm to 900nm

And are used for the visible region. They are typically useful for measuring temperately dilute solution in which change in color strength varies

Significantly with variations in concentration it has life of near 1200h.

2) HYDROGEN OR DEUTRIUM LAMP:

For the ultraviolet region hydrogen or deuterium lamps are commonly

Used there wavelength range from 200nm to 450nm. Deuterium lamps are usually more stable and has a long life of about 500h. This lamp produces

Continuous or discontinuous spectral.

3) XENON FLASH LAMPS:

Xenon flash lamps has numerous advantages which are as follows:

1) There wavelength range from 190nm to 1000nm.

2) They release both ultraviolet and visible wavelength.

3) They have long life

4) They do not heat up the instrument

5) They decrease warm up temperature

2) MONOCHROMATOR :

A monochromator receives polychromatic input light from the lamp

And yields monochromatic light.

Monochromatic means light of single wavelength while polychromatic means light of multiple wavelength.

Monochromatic is consist of three parts:

1) ENTRANCE SLIT:

. The main purpose of the entrance slit is to define the symmetric properties of the examined radiation. The scattering or diffraction is only manageable if the light is collimated.

2) EXIT SLIT:

 The purpose of the prism is to scatter the light into a rainbow. At the exit slit, the colors of the light are spread out. Because each color reaches at a distinct point in the exit slit plane, there are a sequences of images of the entrance slit absorbed on the plane. Because the entrance slit is finite in width, portions of nearby images intersect. The light leaving the exit slit contains the whole image of the entrance slit of the selected color parts.

3) DISPERSION DEVICES:

Dispersion devices causes a dissimilar wavelength of light to be dispersed at different angles which are used for function.

TYPES OF DISPERSION DEVICES:

1) PRISM:

Prism is used to separate different wavelength if a corresponding beam of radiation falls on a prism, the radiation of two dissimilar wavelength will be bend through different angles. Prism may be prepared of glass or quartz. Quartz prism is appropriate for visible region and Glass prism is appropriate for ultraviolet region.

2) FITERS:

Filter separate different parts of electromagnetic spectrum by absorbing and reflecting certain wavelength and transmitting other wavelengths.

THERE ARE TWO TYPES OF FILTERS:

1) ABSORPTION FILTERS:

Absorption filters are glass substrates comprising captivating

Specie that absorb certain wavelength. A characteristic example is

A cut on color filter, which blocks short wavelength light such as

An excitation source, and transfers longer wavelength of light

Such as fluorescence that reaches a sensor.

2) INTERFERENCE FILTER:

Interference filter are prepared of numerous dielectric thin films

On a substrate. They use interference to selectively spread

Or reflect a particular range of wavelengths. A typical example is

A band pass interference filter that transfer a narrow range of

Wavelength from a discharge lamp.

3) DIFFRACTION GRATING:

Diffraction grating is a photosensitive constituent with a regular pattern

Which split light in to numerous beams travelling in different directions.

The path of these beams depend on the spacing of grating

And wavelength of light so that grating acts as dispersive element.

The diffraction grating scatters the light in to linear spectrum which is focused along the light path of the gadget.

• FOCUSING DEVICES:

Focusing devices are mixture of lenses, slit and mirror. Variable slits also permits alterations in the total radiant light reaching the detector.

The Ebert and Czerny turner experiment and their alterations are combination of prism or grating and focusing devices.

OPTICAL MATERIAL:

MIRRORS:

• TYPES OF RAYS                                                    MIRROR SUBSTANTIAL

• XRAYS – ULATRAVIOLET                                    ALUMINIUM

• VISIBLE                                                                   ALUMINIUM

• NEAR INFRARED                                                   GOLD

• ELECTROMAGNETIC                                             copper

4) CUVETTE:

A cuvette is a type of cell closed at one end it is made up of plastic,

Glass or optical grade quartz and designed to grip samples for spectroscopic experiment. Cuvette should be very neat and clear

And without impurities because it may disturb the spectroscopic

Readings. A cuvette may be exposed to the atmosphere and it can

Be sealed by Teflon cap. Cuvettes are designated for transparency in the spectral wavelength of interest.

For visible region cuvettes of optical glass are suitable for dimension

Optical glass absorbs light below 350nm and quartz glass must be used

For these wavelengths. The sample cuvettes are placed in darkened

Investigation chamber which has the capacity to hold several cuvettes.

5) DETECTOR:

Any light sensitive device which can be used as a detector of light.

The photocell and phototube are modest photo detector generating current proportional to the intensity of light.

TYPES OF DETECTOR:

There are two types of detector:

1) SILICON PIN PHOTODIODE:

Blue enhanced for spectral range from 350nm to 1100nm it is considered for low noise and transforming direct current in to bandwidth applications. Applications contain low light level measurement, particle counting and detection of material.

2) GALLIUM NITRIDE OR ULTRAVIOLET DETECTOR:

The family of gallium nitride and ultraviolet detector are schotky treated fully passivated ultraviolet photodiode. There wavelength range from 200nm to 365 nm and is enveloped with a quartz glass.

6) DISPLAY OR READ OUT DEVICE:

The data from the detector are showed by a read out device.

A light beam reflected on a scale or numerical display. The output can

Also be transferred to a computer or printer.

TYPES OF SPECTROPHOTOMETER:

1) SINGLE BEAM:

Single beam spectrophotometer was first created and all

The light passes through the sample in this situation to measure the strength of incident light the sample must be removed so that

All the light can pass through this spectrophotometer is cheaper

And has less difficulty.

• ADVANTAGES OF SINGLE BEAM SPECTROPHOTOMETER:

The single beam spectrophotometer is at low cost and has high                                    quantity and has high sensitivity because its optical system is      Simple.

• DISADVANTAGES:

The basic disadvantage is that it takes elongated time in taking

Reference point and taking the reading of sample because

Of which there are difficulties with drift. It was true for early design but modern instruments have better electronics and more stable lamps.

   

2) DOUBLE BEAM SPECTROPHOTOMETER:

The double beam spectrophotometer project aims to eliminate

Drift by computing blank and sample virtually and simultaneously.

A “chopper” alternately transfers and reflect the light beam so that it travels down the blank and a sample optical paths to a single detector.

The chopper causes the light beam to switch paths at about 50 Hz.

Which are processed to give transmittance and absorbance as output.

ADVANTAGE:

The advantage of double beam spectrophotometer is high permanency because and sample are measured virtually at the same moment in Time.

DISADVANTAGES:

Disadvantages are higher cost, lower sensitivity because throughput of

Light is poorer because of the low complex optics and lower consistency Because of the greater complexity.   

CONCLUSION:

In short the use of spectrophotometers extents various scientific fields, such as physics, matrialscience, chemistry, biochemistry and they are extensively used in several industries including semiconductors, laser and optical engineering, printing and scientific examination, as well in research laboratory for the study of chemical substances. Eventually, a spectrophotometer is able to govern, dependent on the control or calibration, what constituents are present in a target and exactly how much through calculations of observed wavelengths.

In the end it is very useful for measuring spectral range.

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