Lecture 10

Added: 2026-05-09

[00:00:03][music] [music] Hello everyone, welcome back to the MOO's course on advanced analytical technique. We are now entering into the third week of this course and this is the first lecture of the third week where we are going to discuss about the inductively coupled plasma technique which is used as a source of excitation in atomic emission spectroscopy.

[00:00:42]My name is Dr. Mohammed Zan Khan and I have been working as assistant professor in the department of industrial chemistry amiger. Let us begin with the let us begin with today's lecture.

[00:00:54]inductively coupled plasma technique or the ICP technique which is coupled with an AES and used as an which is coupled with an atomic emission spectroscopy technique and used as excitation source.

[00:01:08]This ICP is also known as ICP AES.

[00:01:13]The inter the inter sorry the the inductively coupled plasma technique which is also known as ICP AES or ICP OEES which means that inductively coupled plasma atomic emission spectroscopy or inductively coupled plasma optical emission spectroscopy. It is one of the widely used method of AES technique. Among all the possible excitation sources like the flame excitation sources, our electrothermal methods like electric arc, AC arc, AC spark and DC spark, AC arc, DC arc and AC spark.

[00:01:58]We always prefer to use plasma sources because with these sources we can attain very high temperatures and these techniques are also um aminable to multiple element analysis simultaneously. And among the available plasma techniques two we have covered in the previous lecture the direct current plasma the microwave plasma and then the ICP inductively coupled plasma. This ICP is one of the widely used technique because we can achieve very very high temperature even up to 10,000° Kelvin by this technique and it is very useful for multiple sample analysis. It has been used for over 30 years and it is considered as one of the most versatile method for the inorganic analysis means for the analysis of elements. And with this technique and with this technique we can analyze all alkaly metal, alkaline earth metals, transition metals, metaloids, lenthnides and few actctinides.

[00:03:05]By this technique even carbon, nitrogen, oxygen and sulfur, these nonmetals can also be analyzed by this technique for in it is one of the most versatile method for inorganic analysis which means it can be used for the analysis of elements. Friends like alkali metals, alkaline earth metals like alkali metals, alkaline earth metals, transition metals, metaloids can also be analyzed by this technique and we can also go for lenthnides as well as few actctinides.

[00:04:01]Further some nonmetals like carbon, nitrogen, oxygen and sulfur are also studied by ICP technique.

[00:04:13]Just like direct current source plasma and microwave plasma, it also uses an argan gas uh an inert gas like argan to create this plasma and it provides very high accuracy as well as it minimizes the possibility of formation of oxides as well as nitrites of the metal at such high temperature of over 10,000° Kelvin because we are not using oxygen or any other oxidant we are using an inert gas.

[00:04:39]So the possibility of formation of any um compound like oxides of the metal any com. So the possibility of formation of any compound of the metals like metal oxides or metal nitrites is very low.

[00:04:54]This ICP uses a plasma torch. This is the plasma torch which is basically used to create the plasma. And this plasma torch is made up of quartz.

[00:05:09]For those who are not aware, quartz is a silicate. It is a polymer of SiO2 in which the tetrahedral units of Si4 negative are connected in such a way that each and every oxygen of this silicon tetrahedra is shared with other nearby tetrahedra to create a network of structure and it is represented by SiO2 silica. It is a polymer of silica SiO2 and this is having very high thermal stability. So this quartz and it is very high optical property. It is transparent like glass. So it is transparent. It has very high optical property. So this quartz tube is used and this quartz tube it is uh it contains three tubes coentrics and it contains three coentric quartz tube means we have an outer tube. Then we have a middle tube.

[00:06:09]And finally we have an inner tube. So there are three tubes.

[00:06:15]As you can see this is our inner tube.

[00:06:17]Then these this is our minor tube and this is the outer tube. In all these three tubes we passes argan gas which has different purposes. In the outer tube, we passes argan gas which serves as a coolant gas to maintain the temperature and to avoid the uh damage of this quartz torch or these copper coils which are used as a coil for passing radio frequency.

[00:06:47]In case of ICP just like we use microwaves in case of microwave plasma in case of ICP we uses radio frequency source to create very high magnetic field that has the potential to convert an argan gas an inert gas into its ionized form to create a plasma. So in ICP we use radio frequency which creates very high magnetic field and that ultimately creates a plasma.

[00:07:16]So this torch has it towards. So this torch has these radio frequency coils that are made of copper which are used to pass the radio frequency from the radio frequency source. These coils are connected with a radio frequency source and they are used to pass radio frequency. Then we have as I said three coentric tubes of quartz. The outermost tube is used for passing coolant organ gas to maintain the temperature. Then the middle this the second uh quartz tube the second coentric quartz tube is used for passing auxiliary organ gas.

[00:08:00]The purpose of passing this auxiliary organ gas is to create a plasma. So we need high flow rates here because high flow rates can only be able to sustain such a high plasma. And then this inner tube is used for passing aerosol sample which are already prepared in argan gas.

[00:08:29]So as I said the torch which is made of quartz consist of three coentric tubes and the tubes the outermost tube has a diameter of 2.5 cm. This one this has a diameter of 2.5 cm. So this tube it is the outermost tube which has a diameter of 2.5 cm and it is used for passing coolant gas to control the heat.

[00:08:54]Argan gas in the outermost channel is used for controlling the heat while the argan gas in the middle column is used to create the plasma. And these argan gas moves tangentially. You can they move these gases moves in a tangential manner so as to completely cover up the quartz tube and provide cooling to the whole tube structure.

[00:09:20]This gas which is passed in the middle column is called as auxiliary. This gas which is passed in the middle column is called as auxiliary gas and it it is used for creating the plasma.

[00:09:32]Now as I said the torch is already connected with copper coils which are connected to the radio frequency source.

[00:09:40]So we have radio frequency source al also known as radio frequency generators. Radio frequency sources are sources of electromagnetic radiation with very high wavelength. They are also used in communication services. So they have very high wavelength. These radio frequency source are used with frequency ranging from as low as 5 MHz because even at 5 MHz is it has sufficient energy to create a high magnetic field which is able to create a plasma and we can go up to 100 megahertz of frequency which is of course a very high frequency value for our radio frequency region and at such a high frequency of 100 MHz or 100 into 10 raised ^ 6 herz Herz we can easily create a high temperature with the help of a magnetic field that is capable of converting an inert gas like argan into its plasma.

[00:10:41]Although we the frequency ranges from 5 to 100 but for practical purposes we generally use RF generator with frequency of 25 to 40 MHz. It is very common and these frequency and external power source are basically responsible for creating a magnetic field which then generates a plasma. And these frequency and RF and these RF frequency and these and these RF frequencies are transferred to the quartz torch with the help of copper coils. And these copper coils are surrounding the quartz tube and they are being protected and they are being protected from the high temperature of the plasma by a circulating water bath around it.

[00:11:35]So along with these columns which so along with these coils that are surrounding the torch made of quartz we also passes circulating water which protects this coil from burning.

[00:11:56]So this is the assembly here you you can see we have a plasma torch. This is a spray chamber which is connected. This is spray chamber. Sorry.

[00:12:07]This is spray chamber which is connected to the nebilizer. Nebulizer sucks in the sample, mix it with argan gas. This is argan gas supply. So nebilizer sucks in the sample, mix it with argan gas and then spray the aerosol in this chamber.

[00:12:20]And with this chamber the aerosol enters into the plasma. And finally this sample aerosol molecules are dissolvated, vaporized, converted into their individual atoms and finally excited to create an emission spectrum.

[00:12:38]Now as I said in case of um direct Now as I said in case of direct current plasma as well as for microwave plasma where we um require an argon source of 5 to 10 L. In case of uh direct current plasma we need a 5 liter per minute flow rate of organ. While in case of uh the microwave plasma we can go up to 10 L per minute of organ this much flow rate is required. While in case of ICP inductively coupled plasma we need excessive high rate of plasma because here but in case of ICP we need excessive high rates of argan gas because here the argan gas serves three purpose. The first purpose or the function of organ gas is to convert the sample into the first purpose of this organ gas is to convert the sample into aerosol.

[00:13:38]Then and it enters into the inner column of the quartz tube. We also pass argan gas in the outer chamber or the in the outer tube where it serve as cooling gas.

[00:14:00]Outer tube.

[00:14:05]Outer tube.

[00:14:08]The flow rate in the outer tube is around 13 to 20 L per minute.

[00:14:14]Then it it is also used and then it is mainly used to create the and then it is mainly used to create the plasma where it is passed through the middle tube and called as auxiliary gas in the middle tube where the flow rate is ranging from 5 to 20. Mostly we use 10 to 20 L per minute of this gas. So the flow rate is 10 to 20 liter per minute here then 13 to 20 liter here and then also for creating a aerosol. So very high flow rates are required even higher than our other plasma making techniques like direct current plasma and microwave plasma. Therefore such a high rate is maintained with the help of a dvar separators. As I told you earlier about the DVR separators that it is used to store gases under cryogenic condition means those gases which have very low liquid temperature. In case of argan it is - 185° C.

[00:15:20]In case of nitrogen it is 196°C and in case of helium it is even lower - 260°C.

[00:15:30]So these gases can be stored with the help of these DV bar separators. This So these gases can be stored in liquid form with the help of this DVR flask which is a flask made of either this which is a flask made of iris. This is which is a flask made of a stainless steel.

[00:15:56]And this stainless steel flask has a doublewalled structure means it has two walls.

[00:16:09]This flask is made of two walls of stainless steel and in between these two walls vacuum is created because vacuum helps us to control the heat losses or the flow of heat due to convection and conduction.

[00:16:28]So this portion this is basically the vacuum field region. This this this portion is basically these are the two.

[00:16:37]This is the inner stainless steel flask.

[00:16:42]This is the outer flask. And then in between we have this portion.

[00:16:46]Then this portion is for us to create the vacuum. And in this vacuum this helps us to stop the flow of heat due to conduction and convection.

[00:16:58]And then in the outer part of this stainless steel we provide coating of silver which reflects which stops which reflects all the heat so that the the flask does not absorb any heat and it maint and it does not have any temperature effects and it does not have any temperature effects and it keeps the sample at very low temperature. So this diar flask is used to store liquid fl organ gas that can be very helpful to meet out such a high demand of argan gas. If we calculate the total uh flow rate if we calculate the total argan gas demand it is around 40 to 50 lit per minute which can be maintained with the help of this assembly or the flask.

[00:17:54]Now the formation of plasma as I as I just mentioned that our quartz torch is having these copper coils supported with circulating water to protect them from damage and in this we have three coentric tubes.

[00:18:15]So when the auxiliary argan gas is passes in a tangential fashion uh into the middle column into the middle tube it moves up and through these coils radio frequency is transferred into the torch and the oxillating field of this radio frequency or I should say the oxillating magnetic field of this uh radio frequency And this oxillating magnetic field of the radio frequency provides excessive energy which is sufficient to convert argan gas into its cations ions and electrons.

[00:18:58]So when through these copper Tesla coils and when so when so through these copper so through these Tesla coils when we pass radio frequency which has a fluctuating magnetic field of very high strength this has enough energy to convert the argan gas coming as auxiliary gas in the middle tube to convert it or to ionize it into its kines and electrons creating a plasma which has very very high energy. we can go up to 10,000 Kelvin easily and immediately it can uh excite all the sample convert all the molecules into individual atoms in excited state thereby emitting light radiations creating an emission spectrum but as I said proper supply of argan gas should be maintained as well as for the sustainance of this plasma the magnetic field available through this RF source must be stable. Then only we can generate a stable plasma which is sufficient to convert all the sample even in multiple analysis that is sufficient to create the refractory metals metals with very high melting point into their excited atoms creating or forming an emission spectrum.

[00:20:24]The appearance of the plasma. The plasma appears in the form of this in this conical form and the distance it the plasma is the plasma itself generates a continuum of background radiation. So the plasma is very bright.

[00:20:46]it as it emits a continuum of bright light.

[00:20:57]But as the distance of this plasma from the coils increases, for example, we have coils placed over here, Tesla coils, and the plasma is generated here.

[00:21:08]As we move from these coils, the brightness of the plasma decreases. Although the temperature is still very high but the brightness decreases. Brightness decreases as we moves from the coil above at a distance of around 3 cm the plasma is almost transparent.

[00:21:39]So in that transparent region a point somewhat a point somewhere here we carry out the analysis. So our in so our sample is directly entered at this point so that it immediately comes in contact with the plasma when the region is transparent. So that the chances of background radiation or the chances of absorption are minimal or there are no chances of absorption or background radiation. So the sample with the inner tube in the form of aerosol enters into enters at this point which is at a distance of around 3 cm from the coils.

[00:22:27]So that at this particular point the plasma is almost transparent.

[00:22:35]Here you can see first of all when the sample enters into the plasma this is the sample that is being injected in the form of aerosol. First of all we have drying which means removal of solvent. The solvent is removed.

[00:22:53]Then it under goes vaporization. The sample molecules are which are in the form of aerosol. Now since the solvent is removed, they are converted into their vaporized form or the vapor form. Then they are automized means the molecules are converted into their individual atoms and then finally these atoms are ionized creating electrons and cations.

[00:23:22]So this is our kines along with electrons. This is basically plasma.

[00:23:29]So in this plasma we have argan gas, some electrons, even some unionized argan gas. And if there are any other species although we avoid having some other species but if in case we have some molecular species that are still left then we have traces of those molecular species but we mainly have argan gas kines electrons and some of the unionized argan gas and as I said the region above 3 cm of this coil is transparent and in that transparent region only we carry out the analysis.

[00:24:04]Now let us come to the instrumentation of ICP inductively coupled plasma technique.

[00:24:10]Again ICP since it is it is a part of AES atomic emission spectroscopy. So our ICP inductively coupled plasma or sometimes called as ICP AES inductively coupled plasma atomic emission spectroscopy consists of uh components that are similar to the in components which are used in AES. For example, uh we use nebulizer. Here we know use uh although light source is not needed in AES. So here also we do not need a light source. We need excitation source and ICP itself is an excitation source. So along with ICP we need a nebulizer. Uh then we also need detector and monochrometers. Sometimes uh since ICP is useful for multiple analysis at a time simultaneously since ICP is useful for multiple analysis multiple element analysis simultaneously. So instead of monochromstead of monochrom we can also use polychrom and with polychromter we do not use photo multiplier tubes as a detector because one photo multiplier tube can analyze uh one element at a time. So in that particular case for simultaneous analysis of numerous or for simultaneous analysis of multiple elements we always use u charge coupled devices which are present in solid state array detectors SSA detectors. Anyway, so this ICP is also used for quantitative as well as qualitative technique means we can know means we can identify the type of uh sample it structure as well as behavior and we can also identify its quantity the concentration or the amount of the sample. Again just like all AES technique it first of all convert sample into aerosol by mixing it with inert gas argan and then the same argan gas is used to convert the to create the plasma which burns which excite the sample to create an emission spectrum.

[00:26:16]The excitation source causes automization as well as excitation.

[00:26:19]Automization means the sample molecules are converted into individual atoms and then they are transferred into excited state and then sample elements creates an emission spectrum when their electrons returns back to the ground state.

[00:26:37]As I just mentioned the components as I just mentioned the instrumentation of ICP AES is same just like any other AES technique. We have a we have an excitation source which is it which is ICP in this particular case.

[00:26:52]Then we have nebulizer monochrometer detector and finally an output device or a readout device which is our computer.

[00:27:10]Which is our computer?

[00:27:18]And we also have an output device which is our computer.

[00:27:26]This is the flowheet of the different components. We have a sample container over here which is connected to a nebilizer. The nebilizer inlet pipe is immersed into this sample. The nebilizer sucks in the sample. Then we have a provision for argan gas in this nebilizer. It nebulizer mix the sample with argan gas to create aerosol of the sample in argan gas. Then we have RF. Then we have ICP torch which has outer jacket for uh coolant argan gas.

[00:28:00]Then in the middle tube we use auxiliary argan gas to create the plasma. And in the central tube our aerosol sample where the sample is mixed with argan gas is entered. It is excited. it is automized and excited in the plasma.

[00:28:14]Then it reaches to the monochrometer where selective wavelengths are being uh allowed to pass through it while some of them are excluded or even if we are doing multiple element analysis we can use polychrometers over here. So poly chromators can also be used.

[00:28:32]And then finally we have detector for single element we can use PMT photo multiplier tube for multiple analysis we can use charge coupled devices which are a part of solid state array detectors.

[00:28:45]So we use solid for multiple analysis we use solid state array detector which have charge couple devices and finally we have an amplifier and then the output device to present the spectrum.

[00:29:01]and then the output device to present the spectrum. So this is all about the instrumentation uh of ICP in brief. In the next lecture we'll discuss all these components and especially the polymatters and CCD devices in details because in the previous few lectures we have studied about nebilizers. We have also studied about the photo multiplier tube detectors as well as monochrometers but so far we have um so but so far we have not yet studied about the polychrometers as well as the charge coupled devices which are a part of solid state detector. So that we'll discuss in our next lecture. Till then thank you very much. [music]