Lecture 01

Ajouté : 2026-05-12

[00:00:08][music] Hello everyone, my name is Dr. Dr. Mohammed Zan Khan and I have been working as assistant professor in the department of industrial chemistry al Muslim University Alig in this MO course I'll be talking on the advanced analytical techniques I'll be covering the following topics in this week lectures what is spectroscopy the first topic where we'll discuss about the term spectroscopy and how it can be used to study the structures as well as properties of molecules Then we'll talk of the electromagnetic radiations and the different types of electromagnetic radiations their wavelength and frequency.

[00:01:03]Then we'll move on to the type of spectroscopy means that absorption spectroscopy its principle as well as work instrumentation. I'll also be talking of the emission spectroscopy its principle and working along with the instrumentation. Finally, I'll be talking of the inductively coupled plasma technique which is a type of atomic emission spectroscopic technique and the working principle as well as the instrumentation of ICP.

[00:01:37]These analytical techniques are used for the elemental analysis means the AAS atomic absorption spectroscopy, AES atomic emission spectroscopy and the ICP AES inductively coupled plasma atomic emission spectroscopy.

[00:01:54]So let us begin with spectroscopy. Have you ever wondered about the term spectroscopy?

[00:02:00]Why we use the term spectroscopy and what does it mean and what is the main purpose of spectroscopy?

[00:02:09]Spectroscopy is basically the study of the interaction of electromagnetic radiation with matter. Electromagnetic radiations means X-rays, UV, IR these radiations and the interaction with the matter means the atoms as well as the molecules.

[00:02:26]this and the quantitative measurement of this spectroscopy the quantitative measurement is called as the term spectrometry. So we'll covering up both the these words the spectroscopy the study of the interaction of a emr with matter as well as the quantitative measurement of this interaction.

[00:02:50]As I said the electromagnetic radiations when interact with atoms and molecules this interaction basically gives rise to some spectrum and that spectrum is used to study the structure as well as the properties of molecules. Based on that structure we can identify and or we can study the properties of a molecule.

[00:03:12]As you can see in this figure, we have the electromagnetic radiations which are nothing but the electric and magnetic field oxillating perpendicular to each other. For example, if a subatomic particle is being accelerated in an electric field, it starts vibrating and the vibrations are in different planes perpendicular to each other.

[00:03:37]These are the planes in which you can also see from the figure. And then we have these planes and these are perpendicular to each other. Now these oxillating electric and magnetic field they are being transferred in the form of energy packets which are known as photons. When these photons interact with the atoms and molecules present in a sample, they are being absorbed or sometimes they are some of them are being emitted and based on the absorption or the emission lines, we get different types of spectrum which can be used for the qualitative as well as quantitative analysis of both organic as well as inorganic compounds.

[00:04:24]As I said earlier that while reading this from spectroscopy, have you ever wondered that why it is being used or whenever you have seen the structure of compound?

[00:04:38]Have you ever wondered how this structure has been studied or how this structure has been elucidated?

[00:04:47]How do you know that the molecule of methane has a tetraal geometry with a carbon attached to four hydrogen atoms and the bond length and the bond angle of those atoms?

[00:05:00]For example, a molecule like phenol, it has an aromatic ring with this alternating single double bonds and an O group. You have I know that you have read it in the books. And what is the length of a particular bond and what is the bond angle and what is the geometry? The answer to all these questions is the spectroscopy. It basically helps us to study the structure based on the interaction with EMR. It help us to elucidate the structure of a new compound. It helps us to compare the structure of two compounds. So we can compare the structure.

[00:05:36]So we can so we can compare the structure of two compounds.

[00:05:45]We can also elucidate the structure of an unknown compound by the spectroscopy.

[00:05:56]We can also check the purity of a compound with the help of a spectroscopy. We can identify the geometry of a compound or a molecule by spectroscopy. The bond angles, the types of electrons, the types of transition can be obtained by using different types of spectroscopy.

[00:06:22]This word spectroscopy is quite broad.

[00:06:23]Depending upon the different different types of electromagnetic radiations, we have different types of spectroscopic techniques. Now the most important thing is the electromagnetic radiation. Most of the time we talk of the electromagnetic radiation but I think we should uh have some confusion in mind that what is an electromagnetic radiation. The electromagnetic radiations are nothing but a field of an electric field and magnetic field as I said before oxillating perpendicular to each other and these field are accelerated when a subatomic particle subatomic particles are particles present in an atom like an electron or a proton. So when a subatomic particle is accelerated in electric field, it creates oscillating electric and magnetic field that are perpendicular to each other that are perpendicular to each other and they carry with them energy. Those energy packets are called as photons and they move with a very high speed which is called as the speed of light. And the speed of light it is constant for all types of radiation whether it is gamma rays whether it is x-rays or we have u ultraviolet I or radio waves of course they have different wavelengths they have different lambda they have different frequency or I should say wave number but the velocity V or sometimes it is reported as C is always the same and this velocity is called as the velocity of light which is equal to 29,000 872 kilometers.

[00:08:05]So this the wavelength of these visible radiations is from 4 into 10^ - 7 m to 8 into 10^ - 7 m or I should say uh from 4,000 to 8,000 xrom or in terms of nanometers it is 400 to 800 nanometers and this visible radiations are further divided into seven different colors. the violet, indigo, blue, green, yellow, orange and red with red having the longest wavelength and violet and blue they are having shorter wavelengths. So we can represent these the wavelength of these radiations in terms of whether in in angstrom nanometers or even micrometers are used. These the angstroms they basically covers wavelengths of X-rays and gamma radiations while the nanometer is basically used to represents the ultraviolet and visible radiations and micrometers are microns. They are used for infrared radiations and radiations like microwaves and radio waves they have even higher wavelengths. And as you all know that the wavelength is inversely proportional to the frequency while the energy is directly proportional to frequency. As we are moving from lower to higher wavelengths from X-rays or from gamma rays to X-rays and then finally to UV visible and ultimately the radio waves the wavelength increases while the energy as well as the frequency decreases.

[00:09:39]This figure shows the wavelengths of different electromagnetic radiations and how we can correlate or or as a student you can correlate these wavelengths to different size of the objects. For example, if we start from gamma rays the these radiations are having the highest energy as well as the lowest wavelengths. These wavelength ranges from 0.01 01 angstrom to 1 angstrom means 10 ^ -12 to 10 raised ^ - 10 m and this size is basically the size of an atomic nuclei. So you can relate a gamma radiation the wavelength the and wavelength is defined as the distance covered by radiation in a single cycle.

[00:10:30]For example, if the radiation is moving like this, so that this distance is called as the wavelength. While frequency is defined as the number of cycles per second and the wave number is the number of cycles in 1 cm distance.

[00:10:50]So the wavelength of gamma radiation is so small that it is comparable with the atomic nuclei.

[00:10:58]And similarly since it is having the lowest wavelength they have the higher energy as well as frequency. The frequency of gamma radiations is as high as 10 ^ 20 which is very high frequency values and that is why gamma radiations are considered as the highest energy radiations and they are very lethal and dangerous for human beings. These radiations are emitted by radionucleides and these these radiation these radiations are emitted by radionuclei and these radionuclei which are emitting gamma radiations they are very dangerous. Even these gamma radiations can penetrate metals like iron. However, lead can be used as a shield against gamma radiations.

[00:11:44]Then as we go up from gamma radiations to x-rays the wavelength increases and for x-rays the wavelength ranges from 1 to 100 anstrom means 10^ minus 10 to 10 to the power - 8 m. 10 to the power 10 to 10 the power - 8 m. And similarly their frequency is a bit lower than gamma radiations which means 10 raised to the power 18.

[00:12:20]And the size of wavelength of X-rays can be compared to the size of an atom. And you must be aware that atoms are very small particles and each and everything around us and we ourself are made up of atoms which are for then made up of electrons, protons and neutrons.

[00:12:40]Then we have in in this u series the third radiation is known as the ultraviolet radiation which is also used very widely to study the diff natures nature of different compounds the type of electrons and types of bonding. These ultraviolet radiation al are also present in the radiations emitted by sun and they are also quite dangerous. The wavelength of ultraviolet radiations is of the order of 10 raised to the power minus 8 m or I should say they are in the order of 100 nanome 100 nanome greater than 100 nanometers.

[00:13:21]More precisely, I should say they are from 190 nanome to 760 nanometer, which covers the whole ultraviolet invisible radiation. And the ultraviolet region actually ranges from 190 nanome to 380 nanome.

[00:13:44]And in terms of angstrom it is 1900 to 3800 angstrom.

[00:13:52]There is another region which extend below 1900 angstrom from 1500 angstrom to 1900 angstrom. This region is called as the vacuum ultraviolet region. This region is called as the vacuum region.

[00:14:08]The reason I'll explain sometime some other time that why it is called as the vacuum ultraviolet region but this uh region is below 1900 it extends from 1500 to 1900 strong and the wavelength of and the wavelength of ultraviolet light can be compared with molecules. So the size of molecule is in nanometers from 200 to 600 700 800 nanometers. In angstrom it is from 2,000 to 4,000 xstrom. Then we have the visible radiation. The light which we see the light which is the major portion of radiations emitted by sun.

[00:14:48]These visible radiations also have uh the wavelength quite close to ultraviolet region. Most of the time we use them collectively and all the instrumentation which is available in the market which is available for the study they are basically comprised of both these radiations which are basically called as the UV visible and u visible spectrophotometers which that covers the ultraviolet as well as the visible region. So our visible region ranges from in anstrom it ranges from 3800 to 7 precise value I'm telling you 7600 angstrom most of the time we most of the time we call it as most of most of the time we call it as from 4,000 most of the time we call it is most of the time we call it as from 4,000 to 8,000 angstrom but it actually ranges from 3,800 to 7600 angstrom and the size can be compared to protozones which are very small microorganism.

[00:16:01]Then we have the infrared re regions.

[00:16:05]Then we have the infrared region which is a very big region. This infrared region is further divided into near infrared region. We have infrared region as well as far infrared region. This infrared region has a wavelength range of the order of 10 raised to the power minus 5. And you can compare it with the pin point uh you can compare it with a needle point which is very small that the the the sharp edge of the needle is of the order of the wavelength of uh infrared radiation. And this is as I said it is a very wide it is very broad region. Then we have microwave radiations which are having size of 10 raised to the power minus 2 m means now we are coming around in cm and this size can be compared with butterflies and then finally we have radio waves which are having the longest wavelength and the lowest energy as well as frequency. They have wavelength up to they have wavelength in kilometers. You can see 10 raised to the power 3 m and even more than that. So we can say that radio waves have wavelengths in kilometers and because of their very long wavelengths they are being used in radio communications.

[00:17:30]I would also like to tell you that as the wavelength of a radiation increases the capacity to carry the information increases and that is why radio waves can carry information for long distance without any change. While gamma radiations and x-rays they are having very high energy but they cannot carry information for a very long distance and that is why we use radio waves and that is why we use radio waves for radio communication. Even infrared can also be used.

[00:18:02]I hope you might have heard that the James Web telescope is based on infrared radiations.

[00:18:09]While the Hubble telescope which is used to study the universe and the age of the universe and about the big bang is based on visible radiation the Hubble telescope and therefore since visible radiations have a lower wavelength the the photographs which are obtained from Hubble telescope they are quite they are quite blurry they are quite blurred they are not very clear but if we compare those photographs with the photographs provided provided by the James Webb telescope JMS JWST.

[00:18:43]Those photographs are very high resolution photographs because James web telescope uses the IR radiations that can carry information precise information up to very long distances.

[00:18:56]And one more thing, these spectroscopic techniques as I said they are used for structural identification and properties and quantitative analysis as well. They have real world applications as well.

[00:19:08]For example, the spectroscopy which uses radio waves also called as the nuclear magnetic resonance is the basis of the medical resonance imaging technique which is widely used in medical sciences to study the soft tissues of the body.

[00:19:26]It is based on the magnetic properties and it is used to study different tissues of the body and to obtain high resolution and precise information about it. Similarly, this microwave spectroscopy, it is used to study uh about the big bang. It is also used to study the black body radiations and how a body emits radiations. So these techniques have real world applications as well.

[00:19:57]Then for every wavelength as I said there's a corresponding frequency and then there is a corresponding color temperature as well. I hope you must be aware about the color temperature of a radiation. Each and every radiation and the color it represents corresponds to a particular temperature. And you must be surprised. And you must be surprised that bright light especially the white light is having the highest temperature that can extend from 10 million Kelvin.

[00:20:30]While as we move towards the dark regions the blue, the green and red the temperature decreases and the black color which is not emitting anything just like a black body it is comparatively cooler very very it is very cold as compared to the other region. As we move from black regions towards the bright region red yellow the temperature increases each and every color corresponds to a particular temperature. Thank you uh for patience listening and uh we'll be meeting in the next lecture tomorrow.

[00:21:10]Thank you very much. [music]