BP701T. INSTRUMENTAL METHODS OF ANALYSIS (Theory)
UNIT –I
UV VISIBAL SPECTROSCOPY
1. Spectroscopy = It is the branch of science that deals with the study of interaction of matter with light. OR It is the branch of science that
deals with the study of interaction of electromagnetic radiation with matter.
2. Electromagnetic Radiation
Electromagnetic radiation consists of discrete packages of energy which are called as photons. A photon consists of an oscillating electric
field (E) & an oscillating magnetic field (M) which are perpendicular to each other.
3. Frequency (ν): – It is defined as the number of times electrical field radiation oscillates in one second. – The unit for frequency is Hertz
(Hz). 1 Hz = 1 cycle per second
4. Wavelength (λ): – It is the distance between two nearest parts of the wave in the same phase i.e. distance between two nearest crest or
troughs.
Principles of Spectroscopy
1. The principle is based on the measurement of spectrum of a sample containing atoms / molecules.
2. Spectrum is a graph of intensity of absorbed or emitted radiation by sample verses frequency (ν) or wavelength (λ).
3. Spectrometer is an instrument design to measure the spectrum of a compound.
Absorption Spectroscopy:
1. An analytical technique which concerns with the measurement of absorption of electromagnetic radiation.
2. e.g. UV (185 - 400 nm) / Visible (400 - 800 nm) Spectroscopy, IR Spectroscopy (0.76 - 15 μm)
3. Emission Spectroscopy:
4. An analytical technique in which emission (of a particle or radiation) is dispersed according to some property of the emission & the
amount of dispersion is measured.
5. e.g. Mass Spectroscopy
Lambert’s Law
1. A monochromatic radiation is passed through a solution, the decrease in the intensity of radiation with thickness of the solution is directly
proportional to the intensity of the incident light.
2. Let I be the intensity of incident radiation. x be the thickness of the solution.
Beer’s Law
1. A monochromatic radiation is passed through a solution the decrease in the intensity of radiation with thickness of the solution is directly
proportional to the intensity of the incident light as well as concentration of the solution.
2. Let I be the intensity of incident radiation. x be the thickness of the solution. C be the concentration of the solution. Then
, PRINCIPLES OF UV - VISIBLE SPECTROSCOPY
Besic introdaction
UV-Vis spectroscopy is an analytical technique that measures the amount of discrete wavelengths of UV or visible light that are absorbed by
or transmitted through a sample in comparison to a reference or blank sample. This property is influenced by the sample composition,
potentially providing information on what is in the sample and at what concentration. Since this spectroscopy technique relies on the use of
light, let’s first consider the properties of light.
Light has a certain amount of energy which is inversely proportional to its wavelength. Thus, shorter wavelengths of light carry more energy
and longer wavelengths carry less energy. A specific amount of energy is needed to promote electrons in a substance to a higher energy state
which we can detect as absorption. Electrons in different bonding environments in a substance require a different specific amount of energy to
promote the electrons to a higher energy state. This is why the absorption of light occurs for different wavelengths in different substances.
Humans are able to see a spectrum of visible light, from approximately 380 nm, which we see as violet, to 780 nm, which we see as red.1 UV
light has wavelengths shorter than that of visible light to approximately 100 nm. Therefore, light can be described by its wavelength, which can
be useful in UV-Vis spectroscopy to analyze or identify different substances by locating the specific wavelengths corresponding to maximum
absorbance (see the Applications of UV-Vis spectroscopy section).
Principle of Operation
UV-Vis spectroscopy is based on the interaction between light and matter. When light passes through or is absorbed by a molecule, it can cause the molecule
to vibrate. The wavelength of light that is most strongly absorbed by a molecule is called the absorption maximum. By measuring the absorbance of light at
different wavelengths, it is possible to identify and characterize molecules.
1. The principle of operation for a spectrophotometer is that the wavelength of light is inversely proportional to the size of its aperture.
2. This means that shorter wavelengths will pass through a smaller aperture than longer wavelengths.
3. The monochromator in a UV-Vis spectrophotometer is a disk with a series of slits that can be adjusted to select the desired wavelength.
4. The UV radiation region extends from 10 nm to 400 nm and the visible radiation region extends from 400 nm to 800 nm. Near UV Region: 200 nm
to 400 nm Far UV Region: below 200 nm
5. Far UV spectroscopy is studied under vacuum condition.
6. The common solvent used for preparing sample to be analyzed is either ethyl alcohol or hexane.
Instrumentation
1. A UV-Vis spectrophotometer consists of a light source, a monochromator, a detector, and a data recorder.
2. The light source provides illumination at one or more specific wavelengths.
3. The monochromator is used to select the wavelength of light that passes through the sample.
4. The detector measures the intensity of the light that passes through the sample.
5. The data recorder records the absorbance or transmission of light at each wavelength.
UNIT –I
UV VISIBAL SPECTROSCOPY
1. Spectroscopy = It is the branch of science that deals with the study of interaction of matter with light. OR It is the branch of science that
deals with the study of interaction of electromagnetic radiation with matter.
2. Electromagnetic Radiation
Electromagnetic radiation consists of discrete packages of energy which are called as photons. A photon consists of an oscillating electric
field (E) & an oscillating magnetic field (M) which are perpendicular to each other.
3. Frequency (ν): – It is defined as the number of times electrical field radiation oscillates in one second. – The unit for frequency is Hertz
(Hz). 1 Hz = 1 cycle per second
4. Wavelength (λ): – It is the distance between two nearest parts of the wave in the same phase i.e. distance between two nearest crest or
troughs.
Principles of Spectroscopy
1. The principle is based on the measurement of spectrum of a sample containing atoms / molecules.
2. Spectrum is a graph of intensity of absorbed or emitted radiation by sample verses frequency (ν) or wavelength (λ).
3. Spectrometer is an instrument design to measure the spectrum of a compound.
Absorption Spectroscopy:
1. An analytical technique which concerns with the measurement of absorption of electromagnetic radiation.
2. e.g. UV (185 - 400 nm) / Visible (400 - 800 nm) Spectroscopy, IR Spectroscopy (0.76 - 15 μm)
3. Emission Spectroscopy:
4. An analytical technique in which emission (of a particle or radiation) is dispersed according to some property of the emission & the
amount of dispersion is measured.
5. e.g. Mass Spectroscopy
Lambert’s Law
1. A monochromatic radiation is passed through a solution, the decrease in the intensity of radiation with thickness of the solution is directly
proportional to the intensity of the incident light.
2. Let I be the intensity of incident radiation. x be the thickness of the solution.
Beer’s Law
1. A monochromatic radiation is passed through a solution the decrease in the intensity of radiation with thickness of the solution is directly
proportional to the intensity of the incident light as well as concentration of the solution.
2. Let I be the intensity of incident radiation. x be the thickness of the solution. C be the concentration of the solution. Then
, PRINCIPLES OF UV - VISIBLE SPECTROSCOPY
Besic introdaction
UV-Vis spectroscopy is an analytical technique that measures the amount of discrete wavelengths of UV or visible light that are absorbed by
or transmitted through a sample in comparison to a reference or blank sample. This property is influenced by the sample composition,
potentially providing information on what is in the sample and at what concentration. Since this spectroscopy technique relies on the use of
light, let’s first consider the properties of light.
Light has a certain amount of energy which is inversely proportional to its wavelength. Thus, shorter wavelengths of light carry more energy
and longer wavelengths carry less energy. A specific amount of energy is needed to promote electrons in a substance to a higher energy state
which we can detect as absorption. Electrons in different bonding environments in a substance require a different specific amount of energy to
promote the electrons to a higher energy state. This is why the absorption of light occurs for different wavelengths in different substances.
Humans are able to see a spectrum of visible light, from approximately 380 nm, which we see as violet, to 780 nm, which we see as red.1 UV
light has wavelengths shorter than that of visible light to approximately 100 nm. Therefore, light can be described by its wavelength, which can
be useful in UV-Vis spectroscopy to analyze or identify different substances by locating the specific wavelengths corresponding to maximum
absorbance (see the Applications of UV-Vis spectroscopy section).
Principle of Operation
UV-Vis spectroscopy is based on the interaction between light and matter. When light passes through or is absorbed by a molecule, it can cause the molecule
to vibrate. The wavelength of light that is most strongly absorbed by a molecule is called the absorption maximum. By measuring the absorbance of light at
different wavelengths, it is possible to identify and characterize molecules.
1. The principle of operation for a spectrophotometer is that the wavelength of light is inversely proportional to the size of its aperture.
2. This means that shorter wavelengths will pass through a smaller aperture than longer wavelengths.
3. The monochromator in a UV-Vis spectrophotometer is a disk with a series of slits that can be adjusted to select the desired wavelength.
4. The UV radiation region extends from 10 nm to 400 nm and the visible radiation region extends from 400 nm to 800 nm. Near UV Region: 200 nm
to 400 nm Far UV Region: below 200 nm
5. Far UV spectroscopy is studied under vacuum condition.
6. The common solvent used for preparing sample to be analyzed is either ethyl alcohol or hexane.
Instrumentation
1. A UV-Vis spectrophotometer consists of a light source, a monochromator, a detector, and a data recorder.
2. The light source provides illumination at one or more specific wavelengths.
3. The monochromator is used to select the wavelength of light that passes through the sample.
4. The detector measures the intensity of the light that passes through the sample.
5. The data recorder records the absorbance or transmission of light at each wavelength.
