introduction
Interference is a phenomena
that leads to changes (either positive or negative) in intensity of the analyte signal in spectroscopy.
Interferences in atomic absorption spectroscopy fall into two basic categories, namely, non-spectral and spectral.
1. spectral 2. Non Spectral ( Matrix interference, chemical interference, ionization interference)
PRINCIPLE - atomic absorpion spectroscopy
Atoms of the analyte have a fixed number of electrons.
If the light of a specific wavelength is passed through a flame containing that atom, electrons present in different energy levels, known as orbitals, absorb a certain wavelength and excite to higher energy levels.
The extent of absorption ά the number of ground-state atoms in the flame.
Only for information- The ground state is more stable than the excited state. The electrons spontaneously return back to the ground state. It emits the same amount of radiant energy. This process is called fluorescence. Fluorescence is used in atomic emission spectroscopy.
Brief note on - Instrumentation
The basic components of atomic absorption are:
Light source
Chopper
Atomizer
Burners
flames
Monochromators
Detectors
Amplifier
Readout devices
WORKING PROCESS
Calibration
Quantitative analysis in AAS
Safety measures
Important questions and answer
In this slide contains Interference In Atomic Absorption Spectroscopy and applications.
Presented by: Shaik Gouse ul azam. ( department of pharmaceutical analysis.)
RIPER, anantpur.
In this slide contains Interference In Atomic Absorption Spectroscopy and applications.
Presented by: Shaik Gouse ul azam. ( department of pharmaceutical analysis.)
RIPER, anantpur.
this ppt contain all basic information related to the mass spectrometry like introduction, principle of MS, type of ions, fragmentation processes eg. mcLafferty rearrangement, alpha clevage, sigma bond clevage, retro-diels-alder reaction
this ppt contain all basic information related to the mass spectrometry like introduction, principle of MS, type of ions, fragmentation processes eg. mcLafferty rearrangement, alpha clevage, sigma bond clevage, retro-diels-alder reaction
Atomic absorption spectroscopy is a method of elemental analysis. It is particularly useful for determining trace metals in liquids and is most independent of molecular form of the metal in sample.
Pharmaceuticals: In some pharmaceutical manufacturing processes, minute quantities of a catalyst used in the process (usually a metal) are sometimes present in the final product. By using AAS the amount of catalyst present can be determined.
Atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES) is a spectro analytical procedure for the quantitative determination of chemical elements by free atoms in the gaseous state.
Atomic absorption spectroscopy is based on absorption of light by free metallic ions.
In analytical chemistry the technique is used for determining the concentration of a particular element (the analyte) in a sample to be analyzed. AAS can be used to determine over 70 different elements in solution, or directly in solid samples via electrothermal vaporization
Atomic absorption spectrometry (AAS) is an analytical technique that measures the concentrations of elements.
Atomic absorption is so sensitive that it can measure down to parts per billion of a gram (µg dm–3 ) in a sample.
The technique makes use of the wavelengths of light specifically absorbed by an element. They correspond to the energies needed to promote electrons from one energy level to another, higher, energy level.
Atomic absorption spectrometry has many uses in different areas of chemistry.
Clinical analysis : Analysing metals in biological fluids such as blood and urine.
Environmental analysis: Monitoring our environment – eg finding out the levels of various elements in rivers, seawater, drinking water, air, petrol and drinks such as wine, beer and fruit drinks.
The technique makes use of the atomic absorption spectrum of a sample in order to assess the concentration of specific analytes within it. It requires standards with known analyte content to establish the relation between the measured absorbance and the analyte concentration and relies therefore on the [Beer–Lambert law].
The electrons within an atom exist at various energy levels. When the atom is exposed to its own unique wavelength, it can absorb the energy (photons) and electrons move from a ground state to excited states.
The radiant energy absorbed by the electrons is directly related to the transition that occurs during this process.
Furthermore, since the electronic structure of every element is unique, the radiation absorbed represents a unique property of each individual element and it can be measured.
An atomic absorption spectrometer uses these basic principles and applies them in practical quantitative analysis
A typical atomic absorption spectrometer consists of four main components:
Atomization
Light source,
Atomization system,
Monochromator &
Detection system
Atomization can be carried out either by a flame or furnace.
Heat energy is utilized in atomic absorption spectroscopy to convert metallic elements to atomic dissociated vapor.
The temperature should be controlled very carefully for the conversion of atomic vapor.
At too high temperatures, atoms
Instrumental Method of AnalysisUnit 2 (3) Atomic absorption spectroscopy/AAS/
Atomic flame Photometry
(Part -1)
Introduction- Briefing
Atomic spectroscopy involved three major techniques- Atomic emission spectroscopy,
Atomic absorption spectroscopy, and Atomic fluorescence spectroscopy
Principle, Theory of atomic Absorption spectroscopy
Interferences
Instrumentation-
Type AAS
1. Single beam atomic absorption spectrophotometer
2. Double beam atomic absorption spectrophotometer
the light source/radiation source- that emits the spectrum of the element of inetrest
the atomization system/ absorption cell- in which atoms the sample are produced (flame, graphites furnance etc
the monochromator- for light dispersion
the detection system- which measures the light intensity and amplified the signal
A read out device- that show the reading after it has been processed
Working AAS instrument (B. chopper, C. Flame atomizer - There is two types of burners in common used
1. Total consumption burner
2. Premixed burner
D. Fuel/ oxidant
E. Monochromator- Prism, gratting
F. Detectors-Photomultiplier tube
G. Recorder
Difference between Atomic Absorption Spectroscopy and Atomic Emission Spectroscopy
Advantange and limitation
Applications
HPLC- Introduction, Theory, Instrumentation, Advantage, Applications
High-performance liquid chromatography or commonly known as HPLC, is an analytical technique used to separate, identify or quantify each component in a mixture.
The mixture is separated using the basic principle of column chromatography and then identified and quantified by spectroscopy.
In the 1960s, the column chromatography LC with its low-pressure suitable glass columns was further developed to the HPLC with its high-pressure adapted metal columns.
HPLC is thus basically a highly improved form of column liquid chromatography. Instead of a solvent being allowed to drip through a column under gravity, Solvent is forced through under high pressures of up to 400 atmospheres.
Principle
The separation principle of HPLC is based on the distribution of the analyte (sample) between a mobile phase (eluent) and a stationary phase (packing material of the column). Depending on the chemical structure of the analyte, the molecules are retarded while passing the stationary phase.
Instrumentation
1.Solvent reservoir and degassing system
2. Pumping System (Screw- driven syringe pump, Reciprocating pump, Pneumatic or constant- pressure pump)
3. Sample injection system(Septum injectors, Stop flow septum- less injection, Micro- volume sampling valves)
4. Columns- (1. Guard columns 2.separating column)
5. Detectors( The commonly used detectors in HPLC are
Bulk property detectors- examples
1. Refractive-index detectors
2. Conductivity detectors
Solute property detectors- Examples
1. UV detectors
2. Fluorescence detectors
Multipurpose detectors- Example-
1. Perkin-Elmer 3D system (UV absorption+ fluorescence + conductometric detection altogethers)
Electrochemical Detectors- Examples
1.Amperometric, 2. Coulometric detectors)
6. Recorder( There are various types of data processors; from a simple system consisting of the in-built printer and word processor while those with software that are specifically designed for an LC system which not only data acquisition but features, like peak-fitting baseline correction, automatic concentration calculation, molecular weight determination, etc.) Type of HPLC- Normal phase, Reverse Phase, ion exchange, size exclusion, Applications-Stability study- eg Atropin
Bioassays- HPLC is commonly used for the bioassay and analysis of peptide harmones and some antibiotics- cotrimoxazole, penicillins, sulphates and chloramphenicol
In cosmetic industries- used for analyzing the quality of various cosmetic products such as lipsticks, gels, creams etc
Isolation of Natural pharmaceutically Active Compounds– use in the isolation of different type of Alkaloids and Glycosides ( analysis of cinchona, liquorice, ergot extracts and digitalis.)
Control of microbiological processes- HPLC is used in analyse antibiotics (eg. Tetracyclines, chloramphenicol, strptomycin and penicillins )
Assay of cephalosporins
Advantage, Limitation
Gel chromatography, Introduction, Theory, Instrumentation, Applications .pptxVandana Devesh Sharma
Affinity chromatography- Content-Introduction
Theory
Instrumentation
Applications
Gel chromatography is a type of partition chromatography used for separating different sized molecules.
Gel chromatography is also called Gel permeation chromatography or gel filtration or gel exclusion, size exclusion, molecular- sieve chromatography.
The separation is based on the analyte molecular sizes since the gel behaves like a molecular sieve.
In size exclusion chromatography, the stationary phase is a porous matrix made up of compounds like
cross-linked polystyrene, cross-like dextrans, polyacrylamide gels, agarose gels, etc.
The gel structure being used contains pores of different diameters upto maximum size.
1.The test molecules are washed through a gel column and molecules larger than the largest pores in the gel are excluded from the gel structure.
2. Smaller molecules penetrate the gel and the extent of penetration depends on the molecular size----- This delay their movement through the column
This technique is used for the separation of proteins, polysaccharides, enzymes, and synthetic polymers. Instrumentation- A. Stationary phase- It is composed of semi-permeable, porous polymer gel beads with a well-defined range of pore sizes. eg. Dextran, Agarose, Acrylamide. 2. sample size and concentration- sample is applied in small volume (1-5% of the total bed volume).3. Column parameters- use long column, ratio of column diameter to column length (1:20 to :100). The method or steps used for gel preparation. 4. Choice of eluent/mobile phase- Buffers Ex- Phosphate buffer pH 7, NaCl solution, Ammonium acetate (CH3COO-NH4+ ), Ammonium bicarbonate (NH₄HCO₃) ethylenediamine acetate. 5. Effect of Flow rate- maintain with the help of pump. Elution carried out with buffer at optimal flow rate (Eg- 0.25-5ml/min) to give maximum resolution with optimal separation time.6. Separation of components from the sample-
Separation of component from mixture is achieved with the help of column. The retention volume (VR).7. Detection- Using UV absorption detectors. A graph of Elution Volume (ml) Vs Molecular weight. 7. Detection- Using UV absorption detectors. A graph of Elution Volume (ml) Vs Molecular weight. For calibration of the gel in column – Calibrators - (Proteins of known molecular weight. Procedure for gel filtration technique-1. Preparation of column- 2. Washing of the column- 3. Loading of the sample-4. Elution using mobile phase (buffers)5. Detection of compounds . Applications
Fluorimetry part 2, Instrumentation, single beam and double beam, light sourc...Vandana Devesh Sharma
Flourimetry- instrumentation (single beam and double beam flourimeter),Light source
Monochromators / filters
Sample cells/cuvettes
Detectors and
Polarisers
1.Light sources- The radiant energy required for exciting the fluorescent molecule or fluorophore is supplied by the light source.
The fluorescent molecules become excited only at certain wavelength range of the source, therefore, the source should supply energy only at these wavelengths.
2.Monochromators/Filters
A. Filters- made up of
The glass or dye containing wratten filters
Filters- Primary filter and secondary filter
The primary filter- Selects the UV radiation while
The secondary filter transmits visible fluorescent radiation
B.Monochromators- Prisms, gratings
Now a days prism are more used
Monochromator adjusts the angle which the (of) incident radiation makes with the grating surface after striking.
2 gratings are used 1. for incident light and 2. for emitted light
Sample cells/Cuvettes (Glass Cuvettes,Quartz cuvettes,Matched quartz cuvettes)4. Detectors-
(Photomultiplier tube) Working
Fluorimetry, principle, Concept of singlet,doublet,and triplet electronic sta...Vandana Devesh Sharma
Content-Principle
concept of singlet, doublet and triplet electronic stages,
Internal and external conversions,
Factors affecting fluorescence,
quenching,
Instrumentation and
applications
Types of luminescence including
bioluminescence,
chemiluminescence,
Fluorescence, and
phosphorescence
These various forms of luminescence differ in their method of emitting light.
Bioluminescence
Chemiluminescence
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation
In fluorescence, absorption and emission light takes place in very short time (10-12 or 10-9 seconds)
Fluorescence starts immediately after the absorption of light and stops as soon as the incident light is cut off
Eg -The fluorescent clothes, shoes
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation
In fluorescence, absorption and emission light takes place in very short time (10-12 or 10-9 seconds)
Fluorescence starts immediately after the absorption of light and stops as soon as the incident light is cut off
Eg -The fluorescent clothes, shoes
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation
In fluorescence, absorption and emission light takes place in very short time (10-12 or 10-9 seconds)
Fluorescence starts immediately after the absorption of light and stops as soon as the incident light is cut off
Eg -The fluorescent clothes, shoes
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation
In fluorescence, absorption and emission light takes place in very short time (10-12 or 10-9 seconds)
Fluorescence starts immediately after the absorption of light and stops as soon as the incident light is cut off
Eg -The fluorescent clothes, shoes
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation.
In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation
In fluorescence, absorption and emission light takes place in very short time (10-12 or 10-9 seconds) Fluorimetry
An analytical technique for identifying and characterizing minute amounts of substance by excitation of the substance with a beam of ultraviolet/Visible light and detection and measurement of the characteristic wavelength of fluorescent light emitted.Excited – State Processes in molecules
Principle
Interferences
Instrumentation and
Applications
The principle of flame photometer
is based on the measurement of the emitted light intensity when a metal is introduced into the flame.
The wavelength of the colour gives information about the element and
the colour of the flame gives information about the amount of the element present in the sample.
Flame photometry is one of the branches of atomic absorption spectroscopy.
It is also known as flame emission spectroscopy.
Currently, it has become a necessary tool in the field of analytical chemistry. Used to
Determine the concentration of certain metal ions like
potassium,lithium, calcium, cesium etc. In flame photometer spectra the metal ions are used in the form of atoms.
(IUPAC) Committee on Spectroscopic Nomenclature has named this technique as flame atomic emission spectrometry (FAES). Principle of Flame photometer
The compounds of the alkali and alkaline earth metals (Group II) dissociate into atoms when introduced into the flame.
Some of these atoms further get excited to even higher levels. But these atoms are not stable at higher levels.
Hence, these atoms emit radiations when returning back to the ground state.
These radiations generally lie in the visible region of the spectrum.
Each of the alkali and alkaline earth metals has a specific wavelength. Instrumentation-Source of flame, Nebuliser, Monochromator(Prism monochromator, Grating monochromators)DETECTOR (
The radiation emitted by the elements is mostly in the visible region and measured by photo detector. Hence conventional detectors like photo voltaic cell or photo tubes or photomultiplier tube is used), READ OUT DEVICE
[The signal from the detector is shown as a response in the digital read out device. The readings are displayed in an arbitrary scale (% Flame Intensity).], working of flame photometer, Advantages and disadvantage of flame photometer, Errors /interference in Flame Photometry-Flame Temperature, chemical interference, Radiation interference
Application of flame photometry
Potentiometry, Electrochemical cell, construction and working of indicator an...Vandana Devesh Sharma
Potentiometry - Electrochemical cell -Construction and working of reference (Standard hydrogen, silver chloride electrode and calomel electrode)
Indicator electrodes (metal electrodes and glass electrode)
Methods to determine end point of potentiometric titration
and applications
Potentiometry is the method to find the concentration of solute in
A given solution by measuring the potential between two Electrodes
(reference and Indicator electrode) . Potentiometric titration involves
the measurement of the potential of the indicator electrode and
reference electrode.
In potentiometric titration reference and indicator electrodes are
immersed in the solution of particular analyte (titrand) and
potential of indicator electrode is measured with relation to
reference electrode.
Titrant is added in analyte (Titrand) and change in potential is noted
down.
At the end point there is sharp change in potential on indicator
electrode.
Graph is plotted between the indicator electrode potential and
volume of titrant added.
This method is used for determination of sharp end point.
Types of Potentiometric Titration
1. Acid-base titration 2. Redox Titration 3.Complexometric titration 4. Precipitation Titration
content- Principle
Ilkovic equation
Construction and working of dropping mercury electrode and rotating platinum electrode
Applications
Polarography is a voltammetric technique in which chemical species (ions or molecules) undergo oxidation (lose electrons) or reduction (gain electrons) at the surface of a dropping mercury electrode (DME) at an applied potential. Polarography only applies to the DME.
Objective of polarography
Polarography is an electroanalytical technique that measures the current flowing between two electrodes in the solution (in the presence of gradually increasing applied voltage) to determine the concentration of solute and its nature respectively
Polarography is based upon the principle that gradually increasing voltage is applied between two electrodes, one of which is polarisable (dropping mercury electrode) and other is non-polarisable and current flowing between the two electrodes is recorded.
A sigmoid shape current-voltage curve is obtained from which half wave potential as well as diffusion current is calculated.
Diffusion current is used for determination of concentration of substance.
Half wave potential is characteristic of every element.
Ilkovic equation is a relation used in polarography relating the diffusion current (id) and the concentration of the non-polarisable electrode, i.e., the substance reduced or oxidised at the dropping mercury electrode (polarisable electrode).
Definitions of types of currents
1. Residual current (ir), 2. Migration current (im): , 3. Diffusion current (id) 4.Half wave potential 5. Limiting current (il)
Dropping mercury electrode- Dropping mercury electrode (DME) is a polarisable electrode and can act as both anode and cathode.
The pool of mercury acts as counter electrode,
i.e., anode if DME is cathode or
cathode if DME is anode.
The counter electrode is a non-polarisable electrode.
To the analyte solution, electrolyte like KCl is added i.e., 50-100 times of sample concentration.
Pure nitrogen or hydrogen gas is bubbled through the solution, to expel (remove) out oxygen.
Eg: If the analyte solution contains cadmium ions, then cadmium ions are discharged at cathode (-)
Cd2+ + 2e- → Cd
Then, gradually increasing voltage is applied to the polarographic cell and current is recorded.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound and this is used in qualitative analysis.
Graph is plotted between voltage applied and current. This graph is called Polarograph and the apparatus is known as Polarogram.
The diffusion current produced is directly proportional to concentration of analyte and this is used in quantitative analysis.
The half wave potential is characteristic of every compound
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
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Acetabularia Information For Class 9 .docxvaibhavrinwa19
Acetabularia acetabulum is a single-celled green alga that in its vegetative state is morphologically differentiated into a basal rhizoid and an axially elongated stalk, which bears whorls of branching hairs. The single diploid nucleus resides in the rhizoid.
A Strategic Approach: GenAI in EducationPeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
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How to Make a Field invisible in Odoo 17Celine George
It is possible to hide or invisible some fields in odoo. Commonly using “invisible” attribute in the field definition to invisible the fields. This slide will show how to make a field invisible in odoo 17.
2. Interference is a phenomena
that leads to changes (either positive or negative) in intensity of
the analyte signal in spectroscopy.
Interferences in atomic absorption spectroscopy fall into two
basic categories, namely, non-spectral and spectral.
Interferences in AAS
Spectral
Non-spectral
Matrix Ionization
Chemical
3. Spectral interferences are caused by presence of:
1.another atomic absorption line,
2.or a molecular absorbance band close to the spectral line of
element of interest.
Most common spectral interferences are due to molecular
emissions from oxides of other elements in the sample.
The main cause of background absorption is presence of
undissociated molecules of matrix that have broad band
absorption spectra and tiny solid particles, unvaporized solvent
droplets or molecular species in the flame which may scatter
light over a wide wavelength region. When this type of non-
specific adsorption overlaps the atomic absorption of the
analyte, background absorption occurs.
The problem is overcome by:
1.measuring and subtracting the background absorption from the
total measured absorption to determine the true atomic
absorption.
4. 2.by choosing another line for the analyte. For example, a
vanadium line at 3082.11 Ao
interferes with aluminum line at
3082.15 Ao
.
This interference is avoided by employing the aluminum line at
3092.7 Ao
1. Matrix Interference
When a sample is more viscous or has different surface tension
than the standard, it can result in differences in sample uptake
rate due to changes in nebulization efficiency.
The problem is overcome by:
Such interferences are minimized by matching as closely as
possible the matrix composition of standard and sample.
2. Chemical Interference
If a sample contains a species which forms a thermally stable
compound with the analyte that is not completely decomposed by
the energy available in the flame then chemical interference exists.
5. Refractory elements
such as Ti, W, Zr, Mo and Al may combine with oxygen to form --
---thermally stable oxides.
The problem is overcome by:
Analysis of such elements can be carried out at higher flame
temperatures using nitrous oxide – acetylene flame ----instead
of air-acetylene to provide higher dissociation energy.
or
Alternatively, an excess of another element or compound can be
added e.g. Ca in presence of phosphate produces stable calcium
phosphate which ---reduces absorption due to Ca ion.
If an excess of lanthanum is added it forms a thermally stable
compound with phosphate and ----calcium absorption is not
affected.
6. 3. Ionization Interference
Ionization interference is more common in hot flames.
The dissociation process does not stop at formation of ground
state atoms.
Excess energy of the flame can lead to--- ionization of ground
state atoms ---by loss of electrons thereby ---resulting in
depletion of ground state atoms.
In cooler flames such interference is encountered with easily
ionized elements such as alkali metals and alkaline earths.
The problem is overcome by:
Ionization interference is eliminated by adding an excess of an
element which is easily ionized ----thereby creating a large
number of free electrons in the flame ----and suppressing
ionization of the analyte.
Salts of such elements as K, Rb and Cs are commonly used as
ionization suppressants.
9. Atomic absorption spectroscopy is a precise analytical
technique.
It is used for the quantification of metals present in the analyte.
It is one of the best techniques to detect the sample at trace
levels such as part per billion (ppb).
Atomic absorption spectroscopy was developed by Alan Walsh in
the 1950s.
This technique involves the absorption of radiant energy (usually
ultraviolet and visible) by a bunch of free atoms.
The sample used is in a gaseous state.
When an atom absorbs light of a specific wavelength, it results in
the excitation of electrons from the ground state to the excited
state.
The energy absorbed per mole is fixed and can be used for
qualitative and quantitative analysis.
10. PRINCIPLE
Atoms of the analyte have a fixed number of electrons.
If the light of a specific wavelength is passed through a flame containing
that atom, electrons present in different energy levels, known as orbitals,
absorb a certain wavelength and excite to higher energy levels.
The extent of absorption ά the number of ground-state atoms
in the flame.
Only for information- The ground state is more stable than the excited
state. The electrons spontaneously return back to the ground state. It emits
the same amount of radiant energy. This process is called fluorescence.
Fluorescence is used in atomic emission spectroscopy.
Instrumentation
The basic components of atomic absorption are:
1. Light source
2. Chopper
3. Atomizer
4. Burners
5. flames
6. Monochromators
7. Detectors
8. Amplifier
9. Readout devices
12. 1. LIGHT SOURCE
A hollow cathode lamp is used as the light source.
As the name suggests, it consists of a cylindrical hollow cathode
made up of the same element under consideration.
The anode is made up of tungsten.
Both anode and cathode are enclosed in a glass tube with a
quartz window.
The glass envelope is filled with inert gases (Ar, Ne) under
reduced pressure (1-5 torr).
When a high voltage (300-500 V) is applied across the
electrodes, it ionizes noble gases at the anode (+).
The ions produced as a result are accelerated toward the
cathode (-). When these fast-moving ions strike the surface of
the cathode, they cause some of the metal atoms to sputter.
Thus, the electrons of vaporized metals are excited to higher
energy levels. It is due to continuous collision with higher energy
gas ions.
13. 2. CHOPPER
A chopper is a rotating wheel between a hollow cathode lamp and a
flame.
It removes large droplets and allows uniform size droplets to enter
the flame.
It breaks the steady light from the lamp into pulsating light. This
gives the pulsating current in the photocell that is amplified and
recorded without any interference.
3. Sample introduction system
This is used to transfer samples to the atomizer.
It should produce no interference, must be independent of sample
type, and universal for all atomizers.
Pneumatic nebulizers are commonly used for introducing solutions.
A jet of compressed air, nebulization gas, aspirates and nebulize the
solution when the sample is sucked through the capillary tube.
Types of nebulizers
Concentric nebulizers
Angular or crossflow nebulizers
14. 4. Atomizers
The analyte is broken into the free atoms with the atomizer.
For this purpose, a very high temperature is required.
Only a portion of the sample solution is introduced into the
burner chamber through the nebulizer.
In the bottom of the chamber, large particles are accumulated.
These are then drained off.
5. Atomization sources
Burners
These are the basic types of burners used in atomic absorption
spectroscopy.
Total consumption burners
In the total consumption burner, the sample solution, the fuel
(usually acetylene), and the oxidizing gases enter through
separate passages at an opening in the base of the flame.
Here gases create a partial vacuum and force the sample to
move up through capillary action.
15. Premix chamber burners
In premix chamber burners, the sample is aspirated through a
nebulizer and sprayed as a fine aerosol into the mixing chamber.
Here the sample is mixed with fuel and oxidant gases and carried
to the burner head where atomization takes place.
6. Flames
Flame is generally produced by using a mixture of gases. There
are two types of flames commonly used in atomic absorption
spectroscopy.
Air acetylene flame
Nitrous oxide acetylene flame
7. Monochromators
The function of a monochromator is to select the specific
wavelength of light that is being absorbed by the sample.
Types of monochromators
Prism
Diffraction gratings
16. Dispersion from the grating is more uniform than dispersion from
the prism.
So, the grating can maintain a higher resolution over a longer
range of wavelengths.
8. Detectors
Photomultiplier tubes are the most commonly used detectors in
atomic absorption spectroscopy.
These are used to convert electromagnetic waves into electric
currents.
They are made up of photoemissive cathodes and dynodes.
These dynodes provide electron multiplications.
Photodiode array detectors
These detectors convert the transmitted light signals into an
electric pulse.
9. AMPLIFIERS
The output from detectors is fed to amplifiers which amplify the
current several times.
17. 10. Readout devices
Readout systems used in atomic absorption spectroscopy are
meters, chart recorders, digital display meters, etc. hard copies
can make on chart recorders, printers, or plotters.
WORKING PROCESS
Generally, the samples for atomic absorption spectroscopy
analysis should be in solution form.
The steps involved in the analysis are -
Conversion of sample into solution form.
Preparation of blank solution.
Preparation of a series of standard solutions.
Setup instrumental parameters
Measure the absorbance of standard solutions
A plot calibration curve (concentration vs absorbance)
Measure the absorbance of the sample solution.
The unknown concentration of the element is calculated from
the calibration curve.
18. Calibration
The instrument must be calibrated before analysis for better
results.
There must be five standard solutions containing a known
concentration of metals to be analyzed for calibration of the
instrument and of the same concentration as the sample
solutions.
Calibrating solution is generally prepared as a sample of salt
dissolved in water or dilute acid.
The calibration curve is plotted between concentration and
absorbance.
ABSORPTION SPECTRUM
It consists of a series of well-defined extremely narrow lines
arising from the electronic transition of the outermost electrons.
19. Quantitative analysis in AAS
Quantification of elements is done by plotting calibration curves.
At least four standards and a blanks solution are required to plot
a linear calibration curve of absorbance versus concentration.
In all absorbance measurements, the reading must be taken after
the instrument zero has been adjusted against a blank which
may be distilled water or a solution of similar composition to the
test solution.
Usually, standards are measured in the order of increasing
concentration.
After making the measurement with one solution, distilled water
is aspirated into the flame to remove all the traces of the
solution before proceeding to the next solution.
At least two to three separate readings should be taken and then
averaged.
20.
21. Safety measures
The atomic absorption room must be properly ventilated and
provided with an adequate exhaust system with airtight joints on
discharged side.
Gas cylinders must be fastened securely outside the room well
away from heat or ignition sources.
Pipes that carry the gas from cylinders must be securely fixed to
avoid damage.
Make periodic checks of leaks by applying soap solution to joints
and seals.
Never run acetylene gas at higher pressure (maximum 15 psi).
Tubes should be made of brass are other substances which
contain copper of less than 65%.
Never analyze the flame or hollow cathode lamp directly. (uses
protective eyewear).
When the atomic absorption spectrophotometer is turned off,
close the gas supply valve tightly, and bleed the gas line to the
atmosphere through exhaust systems.
22. What is the principle of atomic absorption spectroscopy?
When monochromatic light is passed through a flame containing the atom
under consideration, then the part of the light will be absorbed by the
electron of the atoms atom that causes the excitation. The extent of
absorption is proportional to the number of ground-state atoms.
What is the significance of the atomic absorption technique?
Atomic absorption is a technique used for the detection of metals in
solution at trace. It gives relative analysis such that every element is
detected one by one.
Which detector is used in atomic absorption spectroscopy?
There are two types of detectors used in atomic absorption spectroscopy i.e,
film and photomultipliers.
How accurate is atomic absorption spectroscopy?
Atomic absorption spectroscopy is a very accurate technique for the
detection of metals. It can detect the elements up to 0.1 µg/ mL. Since It is
100 times more precise than UV visible spectroscopy.
Which is the correct order instrumentation of AAS?
Order of instrumentation of AAS:
1. Light source
2. Chopper
3. Atomizer
4. Monochromators
5. Detectors
6. Amplifier
7. Readout devices
23. What can atomic absorption spectroscopy be used for?
Atomic absorption spectroscopy is used for the detection of metal at trace and ultra-
trace levels.
Atomic absorption spectroscopy is used for geochemical and metallurgical analysis.
It is used for the detection of metals in biological fluids i.e blood, and urine.
Atomic absorption is used for pharmaceutical analysis.
After absorption in Atomic Absorption Spectrometry AAS do electrons re-emit the
absorbed light?
When an electron absorbs energy the goes to a higher energy state. They remain in the
excited state for a while and come back to the ground state by emitting the absorbed
energy. Because the ground state is more stable than the excited state.
Why are nonmetals not detected by atomic absorption spectroscopy?
Metals are detected through atomic absorption by their ionization whereas, nonmetals
do not ionize. That’s why nonmetals are not detected by atomic absorption
spectroscopy.
What is atomic spectroscopy?
Spectroscopy is the interaction of light with matter. When we studied this interaction at
the atomic level then this is known as atomic spectroscopy.
What is the difference between a molecular absorption spectrum and an atomic
absorption spectrum?
A molecular spectrum is a study of molecules. It shows light absorb by the whole
molecule. The molecular spectrum has a broad peak. while atomic absorption has a
sharp distinct peak. It shows the light absorb by the atom.
What is the difference between fluorescence spectroscopy and absorbance spectroscopy?
Fluorescence spectroscopy deals with the emission of light when an electron returns to
the ground state. Whereas, absorbance spectroscopy deals with the absorbance of light
by electrons and their excitation.
24. What is molecular fluorescence spectroscopy?
In molecular fluorescence spectroscopy, light energy is used to excite an
electron of certain molecules. When this electron returns to the ground
state they emit light. This emitted light is directly proportional to the
number of atoms present in the analyte.
What elements can AAS detect?
Atomic absorption spectroscopy is used to detect metal atoms.
What are the disadvantages of Atomic Absorption Spectroscopy?
Disadvantages of AAS
Atomic absorption is used only for metals detection.
It cannot be used qualitative analysis
Very high temperature is required for analysis
AAS is a destructive technique
It is an expensive procedure
Toxic and flammable gases are required for analysis
Why are atomic absorption lines very narrow?
The atomic absorption spectrum is very narrow because AAS is a highly
specific method of analysis. Its spectrum displays the characteristic
wavelength absorbed by metal atoms.
What is the detection limit of AAS?
The detection limit of atomic absorption spectroscopy is ranging from ppm
to ppb or 0.1 µg/ mL to 1.0 µg/ mL.
What do AAS and FES stand for?
AAS stands for Atomic absorption spectroscopy whereas FES stands for
flame emission spectroscopy