Aminoglycosides comprise a complex group of drugs derived from soil Actinomycetes in the genera Streptomyces and Micromonospora that impairs ribosome function and has antibiotic potential.
Examples includes Streptomycin, gentamicin, tobramycin, and, amikacin.
Mode of Action:
This complex group of drugs inserts itself on sites on the 30S ribosomal subunit of the prokaryotes and causes the misreading of the mRNA, eventually leading to abnormal proteins.
Structure of the drug:
The aminoglycoside class of drugs comprises one or more amino sugars and an aminocyclitol ring, a 6-carbon cyclic ring.
Coloured portions of the molecule are found in all members of this drug class.
Subgroups and Uses of Aminoglycosides:
The aminoglycoside group of drugs possesses a relatively broad antimicrobial spectrum since they inhibit the synthesis of prokaryotic proteins by binding to one of the ribosomal subunits. Therefore, this group of drugs is mostly used to treat infections generally caused by aerobic gram-negative rods and gram-positive bacteria.
Streptomycin is one of the oldest known drugs. However, it is gradually being replaced by newer forms of drugs that possess less mammalian toxicity. However, even today, Streptomycin is considered an effective antituberculosis agent and an antibiotic of choice for treating bubonic plague and tularaemia.
Gentamicin is less toxic and is widely administered for infections caused by gram-negative rods such as Escherichia, Pseudomonas, Salmonella, and Shigella.
Two relatively new aminoglycosides; amikacin, and tobramycin are also used for gram-negative infections, with tobramycin especially useful for treating Pseudomonas infections in cystic fibrosis patients.
Since this complex group of drugs works by blocking the protein synthesis in prokaryotes, the microbes usually circumvent these drugs by altering the nature of the protein target. Bacteria can thus become resistant to aminoglycosides when point mutations in ribosomal proteins arise.
Aminoglycosides can directly act on the brain and cause seizures. In addition, this group of drugs may damage nerves (very commonly, the eighth cranial nerve), leading to dizziness, deafness, or motor and sensory disturbances.
Aminoglycosides such as gentamicin are nephrotoxic and are poorly cleared by damaged kidneys.
Note: The intake of other drugs must be carefully scrutinized because incompatibilities can result in increased toxicity or failure of one or more of the drugs. For example, the combination of aminoglycosides and cephalosporins increases nephrotoxic effects.
Article by- SAMPRATI PAREKH (MSIWM049)
References: Talaros Foundations in Microbiology – 8thEdition
Enzyme Inhibitor: Enzyme inhibitor decreases the rate of reaction by binding to the substrate or decreasing the turnover number. It can be organic or inorganic.
The process which decreases the rate of reaction, by either binding to enzymes or making configurationally changes is known as enzyme inhibition.
When enzyme poses allosteric side other than active site, allosteric inhibitors bind to the allosteric site causing the configuration change in enzyme, making it less feasible for enzyme to bind with substrate. This type of inhibition is partially reversible, when excess of substrate is added. Km increases and Vmax reduces.
Image source: socratic.org
Allosteric inhibition is mainly of two types
Positive allosteric inhibition: Which increases the Enzyme activity
Negative allosteric inhibition: Which decrease the Enzyme activity
Examples of allosteric inhibition
Inhibitor: ATP and citrate
End Point inhibition: This type of inhibition is also known as Negative feedback inhibition .It is a specialized form of allosteric inhibition, which controls metabolic pathway by regulating various cellular functions. In this type of inhibition end product when formed in excess, it regulate the pathway by binding to the enzymes in reaction, thus controlling production rate.
Weak interaction of inhibitor to enzyme causes reversible inhibition, which can be reverted back to normal by adding excess substrate to compete with inhibitor or by removing inhibitor. This type of inhibition follows Michaelis- Menten rate equation. It has rectangular hyperbolic curve.
When inhibitor binds to the site where substrate binds it causes competitive inhibitor
When inhibitor binds with other site except active site
When inhibitor binds with Enzyme substrate complex, It causes structural distortions
These inhibitors are mainly analogues to substrate
These inhibitors are not analogues to substrate
These inhibitors are not analogues to substrate
Vmax not changed Km increased and Velocity decreases
Vmax decreases and Km remains unchanged
Vmax and Km decreases
Example : Malonate binds Succinate dehydrogenase and competes with Succinate
Example : Ethanol binds with Acid phosphatase
Example: inhibition of placental alkaline phosphatase by phenylalanine
Strong interaction of inhibitor to enzyme causes irreversible inhibition (mostly Covalent interaction). The conformation change caused in Enzyme due to inhibitor is irreversible. Enzyme activity is not regained even by adding or increasing substrate concentration. Vmax decreases and Km is not changed. Suicide inhibition is a specialized form of inhibition, which is also known as mechanism based inactivation. When inhibitor binds to enzyme, it inactivates or complete degradation of enzyme occurs. This type of inhibition does not follows Michaelis- Menten rate equation. It has sigmoidal curve.
Examples: Idoacetate , oxidizing agents etc.
Significance of Enzyme inhibition:
To study Drug action
To study efficiency of enzyme
The interaction of enzyme with substrate can be clearly understood
Elucidating cellular reactions by accumulation of intermediates
Identification of catalytic site
Various drugs used are inhibitors of reaction, so the efficiency of drug and its catalytic function can be clearly known.
THEORY– Plant extractions for DNA is considered one of the tedious methods for high quality DNA isolations. Unlike animal tissues, which have the same tissue type in different species, plant tissues structural biomolecules and metabolites keep changing. Polysaccharides and polyphenols are two very special class of biomolecules that are very different from species to species and thus, becomes a hurdle during DNA isolation. Those biomolecules which contaminated drastically affect the manipulation of DNA isolation.
2gm of plant sample was taken in a motor and 5ml homogenization buffer was added. Then, it was ground well for 15 minutes. Then wash it thoroughly.
15 ml of lysis buffer was added, and it was again ground well for 15 minutes.
The mixture was incubated at 65℃ for 30 minutes in microcentrifuge tubes.
The tubes were then centrifuged at 8000 rpm (rotations per minute) for 10 minutes at room temperature.
500µms supernatant was taken in microcentrifuge tube and equal volume of PCL mixture was added.
Again, tube was centrifuge at 12000 rpm for 10 minutes.
Then, the upper aqueous layer was collected (50 µL) in a new tube and chilled ethanol 200 microliter was added.
Tubes were incubated at -80℃ for 10 minutes or at 4℃ for 1hour.
Tubes were centrifuged at 12000 rpm for 12 minutes.
The supernatant was removed, pellet was air-dried and this is dissolved in µL of TE buffer.
-Submerged fermentation is a type of fermentation in which the microorganisms are suspended in a liquid medium. The liquid medium also contains various other nutrients and growth factors in the necessary proportions in a dissolved or a particulate solids form.
-Submerged fermentation is a technique in which the overall moisture content of the process is high. Therefore, it is better suited for bacteria or other microorganisms that require high moisture contents for growth.
-It is a very widely used technique for many reasons, one prominent one being that the overall purification step is much easier compared to other techniques.
-The main application of submerged fermentation technique is in the extraction of metabolites (secondary metabolites) which are needed to be in liquid form for use.
Figure 1 Overview of the process of submerged fermentation
PRINCIPLE OF SUBMERGED FERMENTATION:
-In submerged fermentation, the growth/development of the desired microorganisms occurs in the liquid environment.
-The primary substrates that are used in this technique are molasses and broth.
-The composition of the broth used is such that the proportion of the broth and the nutrients is such that the production of antibiotics, industrial enzymes etc. is optimum.
-In submerged fermentation, the rate of utilisation of the substrates is high. Therefore, the rate of depletion of them is high. For this reason, the nutrients need to be constantly replenished.
-A specific microorganism is used as the starter culture for this process. This starter organism may be fungi, bacteria or any other suitable organism. A nutrient rich broth is taken in a flask and this starter culture is then inoculated in it to begin the process.
-This technique demands high oxygen levels as the enzymes and other products are produced when microorganisms responsible for production react sufficiently with the broth and the nutrients and break them down to produce the desired products. This process requires oxygen and it is therefore an important aspect of the process.
-In the process, the compounds that are bioactive need to be secreted into the reactant broth/medium.
METHODS OF CARRYING OUT SUBMERGED FERMENTATION:
The primary two types of techniques that are used in submerged fermentation are:
Fed Batch fermentation, and
These are discussed below:
FED BATCH FERMENATION:
In batch-fed fermentation sterilized growth nutrients are added to the culture. Fed batch fermentation is widely used in bio-industries as it helps in the increase of cell densities in the bioreactors. In these processes, the broth is usually highly concentrated to prevent or stop dilution from occurring. To maintain the culture growth rates, the nutrients are added as and when needed. Doing so, promotes the reduction of the risk of overflow metabolism.
Parameters of fed-batch fermenters:
Size- small lab scale fermenters: 1-2 L to 15 L
pilot scale fermenters: 25-100 G to2000 G
large fermenters: 5000 G to 5,00,000 G
Working volume – less than total volume as head space is left to allow to allow aeration, splashing, foaming.
Ph control – This is done by the addition of acid /alkali.
Temperature control – Heating/cooling coils are used for the temperature control inside the bioreactor. In these devices, a ‘heat transfer fluid’ is passed through the coils or the jackets of the devices which help maintain the heat equilibrium.
Agitation: – Impellor: The agitator is mounted on a central drive shaft. Impeller blades are mounted on the shaft. The blades that are used usually cover two thirds of the total diameter of the vessel.
Most batch reactors also use baffles. Baffles are immobile blades. These work by breaking up/promoting the dissipation of the flow with the help of a agitator that rotates. They are usually fixed on the inside wall of the vessel.
Aeration – Aeration is done with the help of a sparger.
–Principal modes of injecting air:
Impeller air injection—air is fed to impeller by hollow drive shaft and then injected into the medium through holes in impeller.
Two phase injection— mixture of air and nutrient medium fed in foam or suspension form
Sparger air injection– air fed by sparger orifices
Advantages: -Initial capital expenditure is lower
-It is simple and feasible to remove contamination, if any occurs during the process,
Disadvantages: – It is less effective for the production of biomass and primary (growth-associated) metabolic products.
-Batch-to-batch variability of the product
-Increased non-productive down-time, involving cleaning, sterilizing, refilling and post sterilization cooling.
-The probes and the instruments may tend to get damaged due to repeated, periodic sterilization processes.
Continuous fermentation: An open system is constructed for continuous fermentation. In continuous fermentation, the rate of utilization of the nutrients by the microorganisms is equal to the rate of input of the externally supplied nutrients and growth factors. Due to this continuous process, a steady-rate of production is achieved.
Working mechanism: -Continuous addition of fresh fermentation medium occurs with constant stirring and agitation.
-Constant volume is maintained by incorporating an airflow weir.
-The rate of removal of broth or the spent fermentation broth is equal to the rate of addition of the fresh medium during the utilization of broth via the microorganisms present.
-There comes a stage then, where the rate at which the microbial cells grow is equal or proportionately equal to the rate at which the cells are displaced.
-The primary variables that need to be maintained to ensure the optimal production of substances using this technique include temperature, pH and gas levels (like oxygen and carbon dioxide).
The examples of the substrates used in submerged fermentation are:
Intellectual property rights (IPR) are designed to allow novel technologies to be available so that the scientist or company receives a reward for the initiative established. Intellectual property possessions can be any codified knowledge, innovation, or anything of actual or potential economic value that has arisen from rudimentary research, analysis, and manipulation of biological systems, industrial application, or for commercial use.
The various types of biotechnological inventions may be grouped into the following-
Approaches/processes of generating useful products.
Numerous products, for example- Antibiotics, vitamins, etc.
Applications of various processes/products, for example, the use of a promoter sequence to regulate gene action.
DNA sequences and the proteins.
Strains of microorganisms, cell lines are obtained by genetic modification.
Methods for genetic modification of organisms.
Patenting of Genes and DNA Sequence–
An artificially synthesized gene is patentable in almost all countries. A patented gene holds exclusive rights to the specific DNA sequence. Once patented, the holder of the patent dictates how the gene needs to be used (whether commercially or clinically) for a minimum of 20 years from the date of the patent. In the USA, genes isolated from the organisms are patentable; gene aroA (shows glyphosate resistance) isolated from a mutant bacterium was the first to be patented. For a patent to be granted in India, it should not be covered in the negative list in Section 39 which provides an extensive list of what are not the inventions under the Indian Patents Act. The act came into force in 1972 amending the Patent act,1970.
The three conditions in order to fulfil the rules imposed by Indian patent act are :
• It should be a novel creation
• It should involve an inventive step for the mankind
• There should be various industrial applications.
Ananda Mohan Chakrabarty got the first US patent for a genetically modified organism in 1981. He discovered a method for cross-linking in such a way that it fixed all the 4 plasmids to a much stabler microbe called Pseudomonas putida capable of consuming 2-3 times faster than previous strains. Its unique characteristic was hydrocarbon degradation, therefore the name was given as “multiplasmid hydrocarbon-degrading Pseudomonas”/superbug. Prof. Chakrabarty’s momentous research has since paved the way for many patents on genetically modified micro-organisms and other life forms for the coming years.
Can Life forms be patented?
The main arguments in favouring the patent of genetically modified life forms are
-They perform novel and useful functions
-They generate economic benefits
-Their production requires large financial and technical innovative inputs
However, the chief objections are usually based on ethical, moral, and religious considerations such as
-They are products of nature and hence should not be fiddled with
-Their genetic modification does not prove an industrial invention
-The inventions cause cruelty to animals
But in 1985, a patent was granted in the USA for a maize plant by overproducing tryptophan through plant tissue culture. Later, in 1988, a genetically engineered mouse called “OncoMouse” was the first mammal to be patented. It was primarily used for cancer research. The animal designed by Philip Leder and Timothy A Stewart of Harvard University used to carry a specific gene called known as an activated oncogene. The activated oncogene increased the mouse’s resistance to cancer, and thus the mouse is a promising model for cancer research. The patenting of OncoMouse, and the extensiveness of the claims made in those patents, were well-thought-out to be unreasonable by many of their colleagues. But, amid the controversies, it was finally patented in 1992.
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:
The orbital σ* (sigma star)
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:
from σ to σ*;
from n to σ*;
from n to π*;
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:
Single spectrometer beam
Spectrometer with double beams
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.
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.
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.
X-ray spectroscopy is a tool that detects and analyses photons with wavelengths in the X-ray section of the electromagnetic spectrum or particles of light. It is used to help scientists understand an object’s chemical and elemental properties. Many distinct X-ray spectroscopy techniques are used in science and technology, including archaeology, astronomy, and engineering. These approaches are used separately to construct a complete image of the substance or entity being studied.
1. In 1901, a German physicist, Wilhelm Conrad Roentgen, was awarded the first Nobel Prize in physics for the discovery of X-rays in 1895.
2. According to the SLAC National Accelerator Laboratory, his new invention was rapidly put to use by other scientists and doctors.
3. Between 1906 and 1908, Charles Barkla, a British physicist, conducted research that contributed to his discovery that X-rays could be typical of individual substances. He also received a Nobel Prize in physics for his work, but not until 1917.
4. In fact, the use of X-ray spectroscopy started a bit earlier, in 1912, beginning with William Henry Bragg and William Lawrence Bragg, a father-and-son team of British physicists.
5. To research how X-ray radiation interacted with atoms inside crystals, they used spectroscopy.
6. By the following year, their method, called X-ray crystallography, had become the standard in the field, earning the Nobel Prize in physics in 1915.
The absorbed photon’s energy lifts an electron from a deeply bound state into unoccupied bound states in x-ray absorption spectroscopy (XAS), or it gains enough energy to exit the atom. Thus, the absorption spectrum provides extensive information on the density of empty states and makes it possible to conclude coordination, the state of oxidation, and much more about the local structure. If the photon’s energy is sufficient to surpass the electron’s binding potential, the likelihood of absorption is affected by the mechanism of electron dispersion from the local atmosphere of the surrounding atoms. This system, called EXAFS, can be used to determine the local structure around the absorbed atoms.
Main parts of this instrument include:
An X-ray source,
The sample holder,
An X-ray monochromator, and
An X-ray is produced from the source by bombarding a heavy metal target with high energy electrons. The spectrum of the energy of the released X-rays influences the option of heavy metal. For instance, a tungsten target generates X-rays of more incredible energy than a silver (Ag) target. Most of the energy that drives this bombardment process is lost as heat, so it is essential to cool the target electrode. More modern sources and other X-ray sources, such as the Stanford synchrotron beamline, are more effective.
a. Source for X-ray:
1. the X-ray source aims to supply the sample with X-ray radiation so that either X-ray Fluorescence or absorption experiments can be carried out.
2. Atoms absorb X-rays from the source, and the wavelength of the absorbed X-ray in X-ray absorbance and the strength of that absorbance provides the identity of that atom, and concentration is consumed.
3. This X-ray absorption causes the electron that absorbs the X-ray to be ionized.
4. The atomic orbital electrons that absorb this light, in their orbitals, are very similar to the nucleus.
5. Absorbed X-rays in X-ray fluorescence cause an atomic electron to be expelled, that is, atomic ionization, and the void is subsequently filled by an electron from an orbital further from the nucleus.
6. The outer electron must emit energy in order to drop down to fill the hole. This emitted light is fluorescence from X-rays.
b. Samples are exposed to X-rays:
1. The monochromator in an X-ray instrument is very different from a wavelength grating or prism monochromator that is visible (400 to 700 nm) or UV (200 to 400 nm).
3. Since the X-ray wavelengths are so short (say, 0.1 to 1 nm), it is not practical to scatter light using a prism or (grating) closely spaced grooves. Instead, contact with crystals of high purity is required; they function like a grating.
4. The crystals are mounted on a movable stage at which the angle at which the incoming X-rays hit the crystal can be continuously and smoothly varied.
5. The angle at which X-rays are detected to disperse from the crystal is also varied at twice the angle of entry.
6. The crystal stage has rotated by 80 degrees in the picture below, so the detector stage has rotated by 160 degrees at this moment.
7. By the collision of X-rays with high purity argon (Ar) gas, the detector mentioned here produces an electronic signal, an X-ray photon transducer.
8. The collision causes Ar ionization and the development of free electrons that flow to a positive electrode. The detector’s current flux between the electrodes is proportional to the incoming X-rays: a signal, Voilà.
c. Detector for X-ray:
1. this double-stage rotation generates the X-ray spectrum with a wavelength on the x-axis and absorbance on the y axis as the detector signal is captured.
2. Energy plotted for a fluorescence spectrum is on the x, and fluorescence emission is on the y axis.
3. An absorbance spectrum is given below. K-edges are considered the shortest wavelength (highest energy) absorbance of elements studied by X-ray.
4. Longer absorbances for wavelengths are L-edge, M-edge. The absorbance edge shape is very typical of the atoms involved in the absorbance when the function is closely examined.
5. To assess the oxidation state of heavy metal atoms and whether the heavy metal atom is bound to carbon or hydrogen, modern K-edge X-ray spectra can be used.
6. In other words, X-ray spectroscopy can be used to determine the chemical environment of heavy metal atoms in complex samples by spectral fitting to the available specifications.
7. The atmosphere here means the environment for atomic bonding.
One of the pioneers who helped in the production of X-ray emission spectroscopy was Karl Manne Georg Siegbahn from Uppsala, Sweden (1924 Nobel Prize). He painstakingly developed numerous diamond-ruled glass diffraction gratings for his spectrometers (also called X-ray fluorescence spectroscopy). He measured high precision X-ray wavelengths of several elements, using high-energy electrons as a source of excitation.
With synchrotrons, intense and wavelength-tunable X-rays are now usually produced. In a material, relative to the incoming beam, the X-rays can suffer a loss of energy. This energy loss of the re-emerging beam reflects the atomic system’s internal excitation, an analogous X-ray to the well-known Raman spectroscopy typically used in the optical field.
Highly accelerated electrons are bombarded with a piece of metal wire called an anticathode. The metal piece becomes a source of radiation from X-ray. With a crystal spectrometer, this radiation can be analyzed.
The spectrum of emissions is composed of two parts:
(a) Continuous spectrum
(b) Line spectrum
It consists of a line spectrum with a continuum of history. X-ray fluorescence generates X-radiation that only has a line spectrum without a continuous spectrum background.
(a). Continuous spectrum:
1. The continuous spectrum depends little on the metal used for the anticathode; with the increase of the metal’s Z, the curve’s height increases, but the curve’s form is independent of z. νmax is entirely independent of the anticathode metal used.
I (v) = constant Z (vmax– v)
2. The curve depends heavily on the voltage V used for electron acceleration.
3. With the voltage V, the maximum frequency increases proportionally.
eV = hvmax
4. Since the continuous spectrum is highly dependent on the velocity of the incident electron, it can be concluded that these electrons emit the corresponding X radiation.
1. They are subjected to intense electrostatic forces arising primarily from the nuclei of the constituent atoms as electrons traveling at high velocities enter the anticathode.
2. The electron is enormously accelerated, and the electrostatic charges emit electromagnetic waves, according to classical radiation theory, and the higher the acceleration, the higher the frequency.
3. It is the sudden slowing down of the electrons responsible for the continuous spectrum when they penetrate the anticathode; this can be defined as deacceleration radiation, but the German term Bremsstrahlung is also used.
1. The spectrum of the line primarily depends on the material from which the X-rays come, either the X-ray tube anticathode or the absorbing material used in a fluorescence experiment.
2. The spectral lines’ frequencies are independent of the electron-accelerating voltage and the incident radiation frequency. It only depends on the chemical components of which the substance is composed.
3. The frequencies are properties of the chemical elements’ atoms.
Several Applications :
In science and technology fields, including archaeology, astronomy, engineering, and health, X-ray spectroscopy is used today.
– By studying them with X-ray spectroscopy, anthropologists and archaeologists can reveal secret knowledge about the ancient artifacts and remains they discover. For example, to determine the sources of obsidian arrowheads produced by prehistoric people in the North American Southwest, Lee Sharpe, associate professor of chemistry at Grinnell College in Iowa, and his colleagues used a tool called X-ray fluorescence (XRF) spectroscopy.
– X-ray spectroscopy also allows astrophysicists to learn more about how space phenomena function.
– Researchers at Washington University, for instance, are preparing to observe X-rays that come from interstellar phenomena, such as black holes, for the future prospectus.
– The team, led by an experimental and theoretical astrophysicist, Henric Krawczynski, is preparing to launch a form of X-ray spectrometer called an X-ray polarimeter.
– The instrument will be suspended in the Earth’s atmosphere by a long-term, helium-filled balloon beginning in December 2018.
– Yury Gogotsi, a chemist and materials engineer at Drexel University in Pennsylvania, uses materials analyzed by X-ray spectroscopy to create spray-on antennas and water desalination membranes.
– The invisible spray-on antennas are only a few hundred nanometers thick but can relay radio waves and steer them.
A technique called X-ray absorption spectroscopy (XAS) ensures that the fragile material composition is right and helps assess the conductivity. To study the surface chemistry of complex membranes that desalinate water by filtering out particular ions, such as sodium, Gogotsi, and his colleagues also use X-ray spectroscopy.
– X-ray spectroscopy can also be used in various medical research and practice areas, such as modern CT scanning machines.
– According to Phuong-Anh T. Duong, Director of CT at Emory University Department of Radiology and Imaging Science, Phuong-Anh T. Duong, Director of CT at Emory University Department of Radiology and Imaging Science, Collecting X-ray absorption spectra during CT scans (via photon counting or spectral CT scanner) may provide more accurate information and contrast on what is going on inside the body, with lower radiation exposures from the X-rays and fewer or no need to use contrast materials (dyes)
b. most convenient and commonly used tool.
c. X-rays are not absorbed by air, so the specimen does not have to be in an evacuated chamber.
Disadvantages of X-rays:
With lighter elements, they do not interact very strongly.
It is a type of electromagnetic spectroscopy that analyses fluorescence from a sample. It is also known as fluorometry or spectrofluorometry. It requires the use of a light ray, usually, ultraviolet light, which excites the electrons of certain compounds in molecules and causes them to emit low-energy light, typically, but not always, visible light. Absorption spectroscopy is a complementary technique. Fluorometers or fluorimeters are called instruments that measure fluorescence.
Theory of Fluorescence spectroscopy:
Molecules have different states, referred to as levels of energy. Electronic and vibrational states are mainly concerned with fluorescence spectroscopy. In general, the species being studied would have an interest in the ground electronic state (a low energy state) and a higher energy excited electronic state. Various vibrational states are within any of these electronic states.
1. In fluorescence spectroscopy, from its ground electronic state to one of the different vibrational states in the excited electronic state, the species is first excited by absorbing a photon.
2. Collisions with other molecules cause vibrational energy to be lost by the excited molecule before the excited electronic state’s lowest vibrational state is reached.
3. The molecule then drops down, releasing a photon in the process to one of the ground electronic state’s different vibrational levels again.
4. The emitted photons have different energies, and therefore frequencies, as molecules can drop down into any of many vibrational levels in the ground state.
5. Therefore, the structure of the various vibrational levels can be calculated by studying the different wavelengths of light emitted in fluorescent spectroscopy and their relative intensity.
The various fluorescent light frequencies produced by a sample are calculated in a standard experiment, maintaining the excitation light at a constant wavelength. It is called the continuum of pollution. An excitation spectrum is measured using different wavelengths of excitation light by recording several emission spectra.
There are two general types of instrument:
a. In order to separate incident light and fluorescent light, filter fluorometers use filters.
b. In order to insulate the incident light and fluorescent light, spectrofluorometers use diffraction grating monochromators.
Both types use the following system:
1. The light passes through a monochromator or filter from an excitation source and strikes the sample.
2. The sample absorbs a proportion of the incident light, and some of the molecules fluoresce in the sample.
3. In all directions, fluorescent light is released.
4. To minimize the chance of emitted or reflected incident light hitting the detector, some fluorescent light passes through a monochromator or second filter and enters a detector usually positioned at 90° to the incident light beam.
5. Various light sources, including lasers, photodiodes, and lamps, can be used as excitation sources, xenon arcs, and mercury vapor lamps in particular.
6. At a very narrow wavelength interval, usually below 0.01 nm, a laser only emits high-irradiance light, making an excitation monochromator or filter unnecessary.
7. The drawback of this approach is, it is impossible to adjust a laser’s wavelength by much.
8. A mercury-vapor lamp is a line lamp, which means that it emits light near peak wavelengths.
9. The xenon arc, on the other hand, has a continuous emission spectrum of almost constant intensity in the 300-800 nm range and ample irradiance for measurements down to just over 200 nm.
10. Fluorimeter filters or monochromators can be used. With an adjustable tolerance, a monochromator transmits light at an adjustable wavelength.
11. A diffraction grating is the most common type of monochromator, i.e., collimated light illuminates a grating and exits depending on the wavelength at a different angle.
12. To choose which wavelengths to transmit, the monochromator can then be modified.
13. The addition of two polarization filters is required to enable anisotropic measurements: one before the emission monochromator or filter and one after the excitation monochromator or filter.
As stated before, the fluorescence relative to the excitation light is most commonly measured at a 90 ° angle. Instead of positioning the sensor at the excitation light line at an angle of 180 ° to prevent interference with the excitation light transmitted, this geometry is used. No monochromator is perfect and some stray light, that is, light with wavelengths other than the target, will be transmitted. An ideal monochromator can transmit only light in the specified range and have a high wavelength-independent transmission. Only the light scattered by the sample induces stray light when measured at a 90° angle and results in a higher signal-to-noise ratio relative to the 180 ° geometry, reducing the detection limit by about a factor of 10000. Besides, fluorescence from the front may also be measured, often done for turbid or opaque samples.
1. The detector can be either single- or multi-channeled.
2. The single-channel detector can only detect one wavelength’s intensity at a time, while the multi-channel detector simultaneously detects the intensity at all wavelengths, rendering the monochromator or filter of the emission unnecessary.
3. The most flexible fluorimetry can record both an excitation spectrum and a fluorescence spectrum with dual monochromators and a continuous excitation light source.
4. When measuring fluorescence spectra, the excitation light wavelength is kept constant, ideally at a high absorption wavelength, and the emission monochromator scans the spectrum.
5. The wavelength going through the emission filter or monochromator is kept constant for calculating excitation spectra, and the excitation monochromator is scanned.
6. As the fluorescence intensity is equal to the absorption, the excitation spectrum is usually similar to the absorption spectrum.
The fluorescence intensity usually is proportional to the concentration of the fluorophore at low concentrations.
1. To achieve ‘real,’ i.e., machine-independent spectra, multiple variables influence and distort the spectra, and corrections are required.
2. Here, the various forms of distortions will be categorized as either instrument or sample-related.
3. Firstly, it addresses the distortion that occurs from the instrument. During each experiment and between each experiment, the intensity of the light source and wavelength characteristics differ over time.
4. Besides, at all wavelengths, no lamp has constant power.
5. To correct this, following the excitation monochromator or filter, a beam splitter may be added to direct a portion of the light to the reference detector.
6. Furthermore, attention must be given to the transmission efficiency of monochromators and filters. These can alter over time as well.
7. Depending on the wavelength, the propagation efficacy of the monochromator often varies. This is the reason why the excitation monochromator or filter should be put after an optional reference detector.
8. The percentage of fluorescence that the detector collects depends on the device as well.
9. Besides, the detector’s quantum efficiency, that is, the percentage of photons detected, differs between different detectors, as the detector eventually deteriorates with wavelength and with time.
10. A tedious method is the adjustment of all these instrumental variables to achieve a ‘normal’ continuum, which is only implemented in practice when it is strictly necessary.
11. This is when the quantum yield is measured. For example, when the wavelength with the highest emission intensity is detected.
As noted earlier, distortions also emerge from the sample. Any elements of the sample must be taken into account as well. Firstly, over time, photodecomposition can decrease the fluorescence intensity. The dispersion of light must also be noticed. Rayleigh and Raman’s scattering is the primary form of scattering in this context. The light dispersed by Rayleigh dispersion has the same wavelength as the incident light, while the dispersed light typically shifts wavelengths to longer wavelengths in Raman dispersion. The dispersion of Raman is the result of a simulated electronic state caused by the light of excitation. The molecules can relax from this virtual state back to a vibrational level other than the vibrational ground state. It is often seen in fluorescence spectra at a constant wavenumber difference compared to the excitation wavenumber, e.g., the peak appears lower than the excitation light in the water at a wavenumber of 3600 cm-1.
The inner filter effects are other things to remember. Reabsorption involves these. Reabsorption occurs because at the wavelengths at which the fluorophore releases radiation, another molecule or part of a macromolecule absorbs it. Any or all of the photons released by the fluorophore may be absorbed again if this is the case. Due to large concentrations of absorbing molecules, including fluorophores, another inner filter effect occurs. The consequence is that in the solution, the excitation light’s strength is not constant, by which a small amount of the excitation light, which is apparent to the detection system, enters the fluorophores. Both the intensity and spectrum of the emitted light are modified by the internal filter effects and must be considered when examining the fluorescent light emission spectrum.
1. Tryptophan is an effective intrinsic fluorescent (amino acid) probe that can be used to estimate the tryptophan microenvironment’s existence.
2. The microenvironment of tryptophan growth changes when conducting experiments with denaturants, surfactants, or other amphiphilic molecules.
3. E.g., if a protein containing a single tryptophan is denatured at a growing temperature in its ‘hydrophobic’ center, a red-shift emission spectrum will appear.
4. Compared to a hydrophobic protein interior, this is due to the proximity of the tryptophan to an aqueous environment.
5. In comparison, if the tryptophan is incorporated in the surfactant vesicle or micelle, the addition of a surfactant to a protein containing a tryptophan exposed to the aqueous solvent can produce a blue-shifted emission spectrum.
6. A fluorophore can be bound to proteins that lack tryptophan.
7. The tryptophan emission spectrum at 295 nm is dominant over tyrosine and phenylalanine’s weaker fluorescence.
Applications of fluorescence spectroscopy:
For the study of organic compounds, fluorescence spectroscopy is used in biochemical, medical, and chemical research fields, among others.
It is used in differentiating malignant, bashful skin tumors from benign tumors has also been documented.
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.
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.
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.
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:
Strong throughput of samples
Simple to make use of
Disadvantages/drawbacks of AAS are as follows:
It is only possible to evaluate solutions.
Less sensitivity compared to the furnace with graphite
Relatively large quantities of samples are needed (1-3 ml)
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).
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.
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.
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.
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.
Glow discharge-spectrometry of optical pollutants (GD-OES)
Laser-Induced Breakdown Spectroscopy (LIBS) (LIBS), also called plasma spectrometry induced by laser (LIPS)
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.
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.
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.
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.
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.
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.