UV-Visible Spectroscopy

BY- K. Sai Manogna (MSIWM014)

Ultraviolet (UV) spectroscopy is an essential physical instrument that utilizes light in the electromagnetic spectrum’s ultraviolet, visible, and near-infrared ranges. The Beer-Lambert law is defined as a linear relationship between absorption, absorber concentration (or absorbing species) in the solution, and path length. Therefore, for a fixed path length, UV-Vis spectroscopy may be used to determine the absorbing species’ concentration. This is a method that is very simple, flexible, quick, precise, and cost-effective. The instrument is called the UV-Vis-NIR Spectrophotometer for ultraviolet-visible (or UV-Vis) spectroscopy. This can be used for the study of liquids, gases, and solids by using radiative energy corresponding to the electromagnetic spectrum’s far and near-ultraviolet (UV), visible (Vis), and near-infrared (NIR) regions. As a result, predetermined wavelengths have been described in these regions: UV ranges in between 300 – 400 nm, whereas visible ranges between 400 – 765 nm, and Near-Infrared ranges in between 765 – 3200 nm. 

Principle: A light beam travels through an object and is determined by the light’s wavelength hitting the detector. The calculated wavelength provides valuable data on the chemical structure and the number of molecules (present in the intensity of the measured signal). Thus, it is possible to obtain both quantitative and qualitative information. Information can be obtained from a wavelength range of 160 to 3500 nm as radiation transmittance, absorbance, or reflectance. Incident power absorption promotes electrons to excited states or anti-bonding orbitals. Photon energy must equal the energy required by electrons to be promoted to the next higher energy state in order for this transition to occur. This method forms the fundamental operating theory of spectroscopy of absorption. Three types of ground-state orbitals can theoretically be involved: 

1. The molecular orbital σ (bonding) 

2. π (bonding) orbital molecular 

3. Atomic Orbital n (non-bonding) 

The anti-bonding orbitals, besides, are: 

1. The orbital σ* (sigma star) 
2. The orbital π* (pi star) 

A transition from the s bonding orbital to the σ anti-bonding orbital involving an electron excitation is called the transition from σ to σ*. The excitation of a lone pair electron (non-bonding electron pair) to an anti-bonding π orbital is likewise expressed by π to π*. Electronic transitions that occur due to UV and visible light absorption are: 

1. from σ to σ*; 
2. from n to σ*; 
3. from n to π*; 
4. from π to π*. 

Fig: Electron transitions in UV-Visible spectroscopy.

Higher energies are included in the transitions s to σ* and n to σ* and thus typically occur in far UV regions or weakly in 180 to 240 nm. Thus, in the UV zone, saturated groups do not demonstrate good absorption. Unsaturated core molecules undergo transitions n to π* and π to π*; these transitions require lower energies and thus occur at longer wavelengths than transitions to anti-bonding orbitals σ*. 

Through the following types of absorption instruments, the UV-Vis spectrum can be recorded: 

1. Single spectrometer beam 
2. Spectrometer with double beams 
3. Simultaneous spectrometer 

All three types of spectrometers have a common light source (mostly tungsten lamps), a smallholder, and a detector. However, besides, a filter can be used to choose one wavelength at a time. This filter is also called a monochromator. A monochromator between the source of light and the specimen is part of the single beam spectrometer. For both wavelengths, the specimen is independently analyzed. The double beam spectrometer uses a single light source, a monochromator, a splitter, and a set of mirrors to direct the beam towards the reference and the sample under investigation. In contrast, a simultaneous spectrometer uses an array of diodes at all wavelengths to simultaneously detect absorbance. The quickest and most potent of the three is this. 

Fig: Single and double beam UV-Visible spectrometer

Fig: Simultaneous UV-Visible spectrometer

Instrumentation: The light source (UV and visible), monochromator (wavelength selector), sample level, and detector are the essential components of a spectrometer. As a light source, a tungsten filament, continuous throughout the UV field, is usually used. Usually, the detector is a photodiode or CCD. To filter light of a specific wavelength, photodiodes go with monochromators to be fed to the detector. The visible lamp must be switched off when tracking the UV spectrum’s absorption, and vice versa. Figure 6 contains a UV-Vis-NIR Spectrometer diagram. 

Components of Instrumental 

A. Source of UV :

1. In its operating wavelength range, the power of the radiating source does not differ. 

2. The continuous UV spectrum is created at low pressures by electrically exciting deuterium or hydrogen. 

3. The UV light generation process involves creating an excited molecular species split into two atomic species and one UV photon. 

4. The emission wavelengths are in the 160 to 375 nm range of both deuterium and hydrogen lamps. 

5. The cuvettes’ content needs to be chosen so that the light incident is not absorbed since this would result in errors in the absorption spectrum obtained. Thus, typically, quartz is used. 

B. Light Source (Visible) 

1. As a visible light source, a tungsten filament lamp is used. 

2. In the 350 to 2500 nm wavelength range, this lamp can produce light. 

3. The energy, i.e., released, is directly proportional to the fourth power of the operating voltage in a tungsten filament lamp. 

4. Thus, a highly stable voltage must be added to the lamp to achieve stable emissions. 

5. By using electronic voltage regulators or constant-voltage transformers, voltage stability is assured. 

6. Tungsten/halogen lamps contain small amounts of iodine, including the tungsten filament, contained within a quartz ‘envelope.’ 

7. The iodine reacts with sublimation-formed gaseous tungsten and creates a WI2 volatile compound. 

8. They decompose when WI2 molecules touch the filament and redeposit tungsten back on the filament. 

9. The tungsten/halogen lamps typically have a lifespan twice the traditional tungsten filament lamp. 

10. Due to their high performance, tungsten/halogen lamps are used in modern spectrophotometers, and their output extends to the UV region as well. 

C. Without Cuvettes

1. The monochromator source is used; light is separated into two sections of equal intensity by a half-mirror splitter before reaching the sample. 

2. One component (or sample beam) passes through the cuvette with the material solution studied in a transparent solvent. 

3. The second beam, or reference beam, passes through a comparable cuvette with only a solvent. 

4. Containers of the reference and sample solution have to be transparent towards the moving beam. 

D. The Detectors 

1. The detector measures the light intensity emitted by the cuvette and sends it to a meter to record and show the values. 

2. The strength of light beams is measured and compared by electronic detectors. 

3. Two detectors have multiple UV-Vis spectrophotometers-a phototube and a photomultiplier tube, and reference and sample beams are simultaneously monitored. 

4. The photomultiplier tube is the detector used widely in UV-Vis instruments. 

5. It requires a photoemissive cathode (when photons strike it, electrons are released from the cathode), several dynodes (when one electron strikes it, a dynode emits several electrons) anode. 

6. The photon incident hits the cathode after it reaches the tube.

7. Furthermore, the cathode releases different electrons, accelerated to the first dynode (whose potential is 90V more positive than cathode). 

8. The first dynode is struck by the electrons, resulting in multiple electrons’ emission with each incident electron. 

9. To create more electrons accelerated towards dynode three, and so on, these electrons are then accelerated towards the second dynode. 

10. At the anode, all the electrons are finally collected. By this time, 106 to 107 electrons had been formed by each initial photon. 

11. Amplified and calculated are the resulting current. Photomultipliers have rapid reaction times and are extremely sensitive to UV and visible radiation. 

12. Photomultipliers, however, are only used for low-power radiation because high-power light will destroy them. 

One example of a multichannel photon detector is the linear photodiode array. These detectors will simultaneously measure both elements of a beam of scattered radiation. A linear photodiode array consists of many tiny photodiodes of silicon produced on a single chip of silicon. The number of photodiodes on a chip can vary from 64 to 4096 sensor components, but 1024 photodiodes are the most common. There is a storage capacitor and a switch for each diode. It would help if you sequentially scanned the individual diode- capacitor circuits. 

Fig: Photodiode array

Charge-Coupled Devices (CCDs) are like detectors for the diode series, but they consist of an array of photo capacitors instead of diodes. 

The reference beam’s strength should have little to no absorption and is called I0, while the sample beam is called I. Within a short time, the spectrophotometer immediately analyses all wavelength components. In order to assess concentration as well as molecular structure or structural changes, this approach is acceptable. It is also used before and after contact with a substrate or molecule to analyze changes in vibrational and conformational energy levels.

Advantages:

1. The instrument’s precision is the most significant benefit for chemists and astronomers who use UV-VIS spectrometers. 

2. Also, small UV-VIS spectrometers may provide highly accurate readings, which are essential when preparing chemical solutions or recording the celestial body’s movement. 

3. It is quick to use UV-VIS spectrometers. Telescopes are connected to most UV-VIS spectrometers used in astronomy. 

4. In chemistry, most of those users are similar in size to electron microscopes and require the same necessary skills to be used. 

5. Since they are easy to handle, there is little risk of inappropriate use of a UV-VIS spectrometer. 

Disadvantages:

1. The primary downside to using a UV-VIS spectrometer is the time it takes to plan for one to be used. Setup is vital for UV-VIS spectrometers. 

2. The region must be cleared of any visible light, electronic noise, or other external pollutants that could interfere with the spectrometer’s reading. 

3. UV-VIS spectrometers are easy to use and provide precise results if the room has been appropriately prepared ahead of time. 

4. However, even a little bit of outside light or vibration from a small electronic device may interfere with the results you hope to achieve when using a UV-VIS spectrometer if the room has not been appropriately prepared.

Atomic absorption spectroscopy

BY- K. Sai Manogna (MSIWM014)

Atomic absorption spectroscopy (AAS) is a method in analytical chemistry for determining the concentration of a specific metal element in a sample. The process can be used in a solution to analyze the concentration of over 70 different metals. While atomic absorption spectroscopy dates from the nineteenth century, a team of Australian chemists primarily developed the modern form during the 1950s. They were headed by Alan Walsh and served in the Chemical Physics Division of the CSIRO (Commonwealth Science and Industry Research Organisation) in Melbourne, Australia. 

By applying characteristic wavelengths of electromagnetic radiation from a light source, atomic absorption spectrometry detects elements in either liquid or solid samples. Wavelengths can be absorbed differently by individual components, and these absorbances are calculated against expectations. In effect, AAS takes advantage of the various wavelengths of radiation that different atoms absorb. In AAS, analytes are first atomized so that their characteristic wavelengths are emitted and registered. When those atoms consume particular energy during excitation, electrons go up one energy level in their respective atoms. 

These atoms emit energy in the form of light as electrons return to their original energy state. There is a wavelength of this light that is characteristic of the element. According to the light wavelength and intensity, relevant elements can be detected, and their concentrations determined according to the light wavelength. 

Principle: 

The approach uses absorption spectrometry to determine an analyte’s concentration in a sample. Thus it relies heavily on the Beer-Lambert rule. In short, by consuming a given amount of energy, the atoms’ electrons in the atomizer can be promoted to higher orbitals for a short period. This quantity of energy is unique to a specific transformation of electrons in a particular element, and each wavelength corresponds to only one element in general. This gives its elemental selectivity to the process. 

Since the amount of energy placed into the flame is known and it is possible to calculate the amount remaining on the other side of the detector, it is possible to estimate from the Beer-Lambert law how many of these transitions have occurred and thus obtain a signal proportional to the concentration of the measured product.

The Instrumentation 

There are four components of the standard AAS instrument: the sample introduction region, the source of light (radiation), the monochromator or polychromator, and the detector. 

It needs to be atomized in order to test a sample for its atomic constituents. The light could then illuminate the sample. Finally, the light emitted is measured through a detector. A spectrometer is usually used between the atomizer and the detector to minimize the effect of the atomizer’s emission (e.g., black body radiation) or from the atmosphere. 

Types of Atomizer:

Usually, the method uses a flame to atomize the sample, but other atomizers are also used, such as a graphite furnace or plasmas, particularly inductively coupled plasmas. 

It is side-long (usually 10 cm) and not deep when a flame is used. The flame’s height above the burner head can be adjusted by changing the fuel mixture’s flow. At its longest axis (the lateral axis), a ray of light passes through this flame and reaches a detector. 

Liquid analysis 

A liquid sample is usually converted in three stages into an atomic gas: 

1. The liquid solvent is evaporated (Drying), and the dry sample remains 

2. Vaporization (Ashing)-the solid specimen vaporizes into a gas 

3. Atomization is divided into free atoms by the compounds that make up the sample. 

Sources of Radiation 

The chosen radiation source has a narrower spectral range than that of the atomic transitions. 

Cathode Hollow Lamps 

The most common source of radiation in atomic absorption spectroscopy is hollow cathode lamps. A cylindrical metal cathode holding the metal for excitation and an anode is inside the lamp, filled with argon or neon gas. Gas particles are ionized when a high voltage is applied to the anode and cathode. Gaseous ions gain sufficient energy to eject metal atoms from the cathode as the voltage increases. Some of these atoms are excited, releasing light with the characteristic frequency of the metal. Various modern hollow cathode lamps are selective for several metals. 

Lasers with diodes 

Lasers, especially diode lasers because of their strong properties for laser absorption spectrometry, can also conduct atomic absorption spectroscopy. The method is then either referred to as diode laser atomic absorption spectrometry (DLAAS or DLAS) or, since wavelength modulation is most commonly used, spectrometry of absorption of wavelength modulation. 

Context Methods of Correction:

The spectral overlap is unusual due to the limited bandwidth of hollow cathode lamps. That is, an absorption line from one element is unlikely to overlap with another. Molecular emissions are much larger, so a specific molecular absorption band is more likely to overlap with an atomic line. This can lead to artificially high absorption and an improperly high measurement of the solution concentration. In order to correct this, three methods are usually used: 

Zeeman correction: A magnetic field is used to break the atomic line into two sidebands. To still overlap with molecular bands, these sidebands are close enough to the initial wavelength, but far enough, they do not overlap with the atomic bonds. It is possible to equate the absorption in the presence and absence of a magnetic field, the difference being the absorption of interest atomically. 

Correction to Smith-Hieftje: This was invented by Stanley B. Smith and Gary M. Hieftje. The high current pulses the hollow cathode lamp, creating more significant atoms and self-absorption population during the pulses. This self-absorption allows the line to be broadened, and the line intensity decreases at the original wavelength. 

Deuterium lamp correction: In this case, for the calculation of background emissions, a different source known as a broad-emission deuterium lamp is used. The use of a specific lamp makes this method the least reliable, but this method is most widely used because of its relative simplicity and the fact that it is the oldest of the three.

Advantages of AAS are given below: 

1. Strong throughput of samples 
2. Simple to make use of 
3. High accuracy 
4. Inexpensive methodology 

Disadvantages/drawbacks of AAS are as follows: 

1. It is only possible to evaluate solutions. 
2. Less sensitivity compared to the furnace with graphite 
3. Relatively large quantities of samples are needed (1-3 ml) 
4. Difficulties with refractory components

Types Of Spectroscopy

BY- K. Sai Manogna (MSIWM014)

Introduction:

Absorption spectroscopy:

Absorption spectroscopy is a technique that compares the power of a beam of light determined before and after a sample contact. It is also referred to as Tunable Diode Laser Absorption Spectroscopy (TDLAS) when done with a tunable diode laser. To decrease the device’s noise, it is most often paired with a modulation technique, most often wavelength modulation spectrometry (WMS) and sometimes frequency modulation spectrometry (FMS). 

Fluorescence spectroscopy: 

To excite a sample, fluorescence spectroscopy uses higher-energy photons, which will then release lower energy photons. This method is known for its biochemical and medical applications and can be used for confocal microscopy, energy transfer of fluorescence resonance, and lifetime imaging of fluorescence. 

X-ray spectroscopy: 

When X-rays with appropriate frequency interact with a material, the atom’s inner shell electrons are excited into empty outer orbitals, or they can be entirely expelled, ionizing the atom. Then electrons from the outer orbitals would fill the inner shell “hole.” In this de-excitation process, the energy available is released as radiation (fluorescence), or other less-bound electrons are extracted from the atom (known as Auger effect). The frequencies (energies) of absorption or emission are characteristic of the individual atom. Moreover, there are minor frequency variations for a single atom that is typical of chemical bonding. These specific X-ray frequencies or Auger electron energies can be determined with an appropriate instrument. In chemistry and material sciences, X-ray absorption and emission spectroscopy are used for determining the elemental composition and chemical bonding. X-ray crystallography is a method of scattering; X-rays are dispersed at well-defined angles by crystalline materials. If the incident X-ray wavelength is known, the distances between the atoms’ planes inside the crystal can be measured. The scattered X-ray intensities provide information about the atomic positions and measure the atoms’ arrangement within the crystal structure.

Flame:

Samples of liquid solution are aspirated into a combination of a burner or nebulizer/burner, dissolved, atomized, and often excited to a higher electronic state of energy. During analysis, the use of a flame includes fuel and oxidant, usually in gases. Gases such as acetylene (ethyne) or hydrogen are used as typical fuel gases. Oxygen, air, or nitrous oxide are common oxidant gases used. These methods can also analyze metallic element analytes in the concentration ranges of part per million, billion, or probably lower. In order to identify light with the analysis data coming from the flame, light detectors are required. 

Atomic Emission Spectroscopy: This technique uses the flame’s excitation; atoms are excited to emit light from the flame’s heat. The total consumption burner with a round burning outlet is usually used in this technique. A more significant temperature flame is usually used to induce analyte atoms’ excitation than atomic absorption spectroscopy (AA). Since the flame’s heat excites the analyte atoms, no particular elemental lamps must shine into the flame. A high-resolution polychromator can be used to generate an emission intensity vs. wavelength spectrum over a range of wavelengths exhibiting multiple-element excitation lines, meaning multiple elements can be detected in one run. Alternatively, a single wavelength monochromator may be set to focus on studying a single element at a specific emission line. A more advanced variant of this process is plasma emission spectroscopy. 

Atomic absorption spectroscopy (often referred to as AA) – A pre-burner nebulizer (or nebulizing chamber) is widely used to produce a sample mist and a slot-shaped burner that gives a longer flame pathlength. The flame temperature is low enough that sample atoms are not excited from their ground state by the flame itself. The nebulizer and flame are used to dissolve and atomize the sample, but for each type of analyte, the analyte atoms’ excitation is achieved by using lamps that glow through the flame at different wavelengths. The amount of light absorbed after passing through the flame defines the analyte quantity in the sample in AA. For greater sensitivity, a graphite furnace is typically used to heat the sample for desolvation and atomization. The graphite furnace process can also analyze any substantial or slurry samples. It is still a widely used analysis method for some trace elements in aqueous (and other liquid samples, due to its strong sensitivity and selectivity. 

Atomic Fluorescence Spectroscopy: A burner with a circular burning outlet is widely used in this technique. To solve and atomize the sample, the flame is used. However, a lamp shines a light into the flame at a particular wavelength to excite its analyte atoms. Then the atoms of some components will fluoresce, emitting light in another direction. For quantifying the amount of analyte component in the sample, this fluorescent light’s strength is used. A graphite furnace is also used for atomic fluorescence spectroscopy. This technique is not as widely used as spectroscopy of atomic absorption or plasma emission. 

Plasma Emission Spectroscopy:

It has virtually replaced in several respects similar to flame atomic emission spectroscopy. 

1. Direct-current plasma (DCP) An electrical discharge between two electrodes creates a direct-current plasma (DCP). It needs a plasma support gas, and Ar is standard. Samples could be deposited on one of the electrodes, or one electrode can be built up by conducting them. 
2. Glow discharge-spectrometry of optical pollutants (GD-OES) 
3. Plasma-atomic emission spectrometry, inductively coupled (ICP-AES) 
4. Laser-Induced Breakdown Spectroscopy (LIBS) (LIBS), also called plasma spectrometry induced by laser (LIPS) 
5. Plasma caused by microwave (MIP) 

Spark or arc/emission spectroscopy – used in solid samples for the study of metallic elements. In order to make it conductive, a sample is ground with graphite powder for non-conductive materials. A sample of the solid was usually ground up and damaged during research in conventional arc spectroscopy methods. The spark or electric arc is passed through the sample to excite the atoms, heating the sample to a high temperature. The excited analyte atoms glow at different wavelengths, producing light that can be detected by standard spectroscopic methods. Since the conditions generating the arc emission are usually not quantitatively regulated, the study is qualitative for the components. Nowadays, under an argon atmosphere, spark sources with controlled discharges allow this method to be considered eminently quantitative, and its use is widely applied worldwide through the production control laboratories of foundries and steel mills. 

Visible Spectroscopy:

Many atoms emit visible light or absorb it. In order to achieve a continuum of fine lines, the atoms must be in the gas phase. It suggests the material has to be vaporized. In absorption or emission, the spectrum is studied. In UV/Vis spectroscopy, visible absorption spectroscopy is mostly paired with UV absorption spectroscopy. While this type may be unusual as a similar indicator is a human eye, it still helps identify colors. 

Ultraviolet light Spectroscopy: 

In the Ultraviolet (UV) field, all atoms are absorbed because these photons are energetic enough to excite outer electrons. Photoionization takes place if the frequency is high enough. In quantifying protein and DNA concentration and protein ratio to DNA concentration in a solution, UV spectroscopy is also used. Several amino acids, such as tryptophan, usually present in proteins, absorb light in the range of 280 nm, and DNA absorbs light in the 260 nm range. For this reason, in terms of these two macromolecules, the 260/280 nm absorption ratio is a good general measure of the relative purity of a solution. It is also possible to make fair estimates of protein or DNA concentration using Beer’s law. 

Infrared Spectroscopy:

The IR absorption spectrum analysis shows what kind of bonds are present in the sample, especially in organic chemistry. The study of polymers and components such as fillers, pigments, and plasticizers is also necessary. 

Raman Spectroscopy:

To study the vibrational and rotational modes of molecules, Raman spectroscopy uses the inelastic scattering of light. An interpretation help is the resulting ‘fingerprints.’ 

Coherent anti-Stokes Raman spectroscopy (CARS) is a recent technique for in vivo spectroscopy and imaging with high sensitivity and robust applications. 

Nuclear Magnetic Resonance Spectroscopy (NMR): 

To determine the various electronic local environments of hydrogen, carbon, or other atoms in an organic compound or other compounds, nuclear magnetic resonance spectroscopy analyses such as atomic nuclei’s magnetic properties. This is used to assist in assessing the compound structure. 

Photoemissions: 

Mossbauer: 

Mossbauer spectroscopy modes of transmission or conversion-electron (CEMS) probe individual isotope nuclei’s properties in various atomic environments by studying the resonant absorption of characteristic gamma-ray energy as the Mossbauer effect.

In the next chapter we will discuss in detail about each spectroscopic methods.

Spectroscopy

BY- K. Sai Manogna (MSIWM014)

Originally, spectroscopy studied the interaction between radiation and matter as a wavelength (λ) feature. Historically, spectroscopy has been applied to the use of visible light, e.g., by a prism, distributed according to its wavelength. The idea later extended to include any calculation of a quantity as a function of either wavelength or frequency. It may thus also apply to an alternating field or changing frequency response (v). 

When the very similar relationship E = h𝛎 for photons was realized, a further extension of the concept’s scope added energy (E) as a variable (h is the Planck constant). A response plot is referred to as a continuum as a function of wavelength, or more generally, frequency.

The spectroscopic method used to determine the concentration or quantity of a given species is spectrometry. In such cases, a spectrometer or spectrograph is the device that conducts such measurements. Spectroscopy/spectrometry can also detect compounds across the spectrum released from or absorbed by them in physical and analytical chemistry. In astronomy and remote sensing, spectroscopy/spectrometry is also extensively used. Many large telescopes have spectrometers used to calculate the chemical composition and physical characteristics of astronomical objects or measure their spectral lines’ speeds from the Doppler shift. 

Methods of Classification: 

Excitation nature: 

1. The spectroscopy type depends on the calculated physical quantity. The quantity that is measured is usually an intensity, either absorbed or created by energy. 
2. Electromagnetic spectroscopy requires material interactions, such as light, with electromagnetic radiation. 
3. Spectroscopy of electrons requires interactions with electron beams. Auger spectroscopy involves inducing, with an electron beam, the Auger effect. In this case, the calculation usually requires the electron’s kinetic energy as a variable. 
4. The interaction of charged species with electric and magnetic fields requires mass spectrometry, giving rise to a mass spectrum. 
5. The word “mass spectroscopy” is deprecated since it is primarily a measurement method, although a spectrum for observation is created. 
6. Mass ‘m’ is a variable in this spectrum, but the calculation is one of the particle’s kinetic energy. 
7. Acoustic spectroscopy requires sound frequency. 
8. Dielectric spectroscopy requires an external electrical field frequency. 
9. Mechanical spectroscopy requires the frequency of external mechanical stress, e.g., torsion applied to a material object. 

Method of Measurement: 

Whether or not they refer to atoms or molecules, most spectroscopic methods are differentiated as either atomic or molecular. Along with that distinction, they can be categorized according to the form of their communication: 

Absorption spectroscopy uses the range in which a material absorbs the electromagnetic spectrum. It involves atomic absorption spectroscopy and different molecular techniques in that area, such as infrared spectroscopy and radio region nuclear magnetic resonance (NMR) spectroscopy. 

Emission spectroscopy uses the electromagnetic spectrum range in which a material radiates (emits). The material must consume energy first. This energy may come from several sources, such as luminescence, which defines the subsequent emission. Spectrofluorimetry includes molecular luminescence techniques. 

Scattering spectroscopy tests the amount of light at specific wavelengths, incident angles, and polarization angles that a material scatters. The method of scattering is much quicker than the process of absorption/emission. Raman spectroscopy is one of the most beneficial applications of light scattering spectroscopy. 

ATOMIC ABSORPTION SPECTROSCOPY

BY- SREELAKSHMI (MSIWM012)

Atomic absorption spectroscopy has proven to be the most powerful method in the use of liquid-density implants since it was introduced by Alan Walsh in the mid-1950s.

More than 60 -70 items including the rarest earth metals determined by this method in the focus from tracking to large numbers. The direct use of this process is limited to instruments other than B, Si, As, Se & Te.

Several non-ferrous metals are weighed with indirect metals. Since atomic spectroscopy does not require sample correction it is an appropriate non-chemical tool as well.

Some elements, especially metals, play a vital role in biological processes, whether they are simple cofactors in enzymes, the atom in the macromolecule of living organisms such as iron in hemoglobin or magnesium in chlorophyll, or as toxins that affect the body.

The use of atomic spectroscopy will make important data available in understanding the biological roles of these substances.

In general, molecules enlarge the band spectra and atoms provide a clearly defined line of line. So, in atomic spectroscopy, the line spectra are studied. These lines are seen visually as light, corresponding to a certain length of the boundaries, which are the atomic emission rays or black lines against the luminous background, which is the atomic absorbing spectra.

On the surface of the element, the wavelength at which the absorption or discharge is detected is associated with changes in which a small change in energy occurs. In general, the appearance of a number of cells, the concentration of atoms is not measured directly in solution but is converted into free atoms.

The process of converting an analyte into a solid, liquid form, or solution into a free gas atom is called atomization. Atoms that are volatilized can be flame or electro thermally in the oven.

In this case, the elements will easily penetrate or emit monochromatic radiation at the right distance. Usually nebulizers (atomizers) are used to spray a standard solution or test in the flame where light is transmitted. Alternatively, the light beam is transferred, to the oven, through a hole containing the inspired apparatus.

Principle

The volatilization of molecules in the sun produces free atoms. These free atoms are happy when light of a certain length is able to emit spectral lines corresponding to the energy required for the electronic transition from the earth’s state to a happy state, allowed to pass through flame. The atomic spectra obtained is fully determined by the object involved and the amount of light concentrated is equal to the number of atoms in the path of light. Therefore, in addition to granting ownership of the material in the sample, this process of viewing and providing information on the quantity of the material.

INSTRUMENTATION

For all types of atom-absorbing spectrometer, the following components are required:

Radiation source:

The source should be such that it emits strong rays of the element to be determined, usually the resonance line of the object. It is almost impossible to separate the maximum length of resonance from a continuous source using a prism or diffraction grating or both at the same time. This problem was solved by the invention of empty cathode emission lamps. Such lamps emit monochromatic radiation element analyzes.

(a) Empty Cathode Lamp:

The cathode contains an empty cup in which the element will be cut. The anode is a tungsten wire. Both electrodes are inserted into a tube containing internal gas (argon or neon). The light window is constructed using quartz, silica or glass. The exact metal depends on the length of the scale to be transmitted. When a potential of approximately 3000V is used between these two electrodes, electrons trigger the immersion of gas into the lamp. These ions which receive enough energy to decompose atoms in the cathode, that is, explode other atoms of iron. These atoms regenerate and when they return to the ground, they begin to release the visible metal used to build the cathode (The light emitted spectrum corresponds to the elevation of the cathode emissions and the gas in the lamp. filling, and selection of very sharp spectral lines to obtain better sensitivity, without cases of disruption caused by other elements). The pressure stored in the lamp is 1 to 5 torr. Each blank cathode lamp emits a wide range of metal used in the cathode; this looks bad as a separate lamp should be used for each item to be analyzed. Another hollow cathode lamp is a wireless emission lamp (EDL) now made available for its light intensity of almost 10-100 times but not as stable as HCL (hollow cathode lamps). They are made of a closed quartz tube containing the salt of the substance and gas entering. The radio frequency field is used to cool the gas which makes the metal ionized. These lamps are usually reserved for items such as As, Hg, Sb, Bi and P.

Working of Atomic Absorption Spectrometer

Practically the meter is adjusted to learn zero absorption when spraying a blank solution in flame and the uninterrupted light of an empty cathode lamp passes through a photomultiplier tube. When a solution with a suction type is inserted then a portion of the light is applied which leads to a decrease in the intensity of the light which falls into the photomultiplier and produces a deviation from the meter needle. Standard object solutions are used to create a measuring curve where the content of the test solutions can be measured.

Applications

• Used to determine the trace of a metal in a liquid.
• Used in clinical laboratories for the removal of body fluids.
• Estimation of soil and water samples.
• Determination of lead in petrol.
• Determination of metallic elements in food industry