CH3 Atomic Spectroscopy 2.pptx PDF

Analytical Chemistry 3 – Atomic Spectroscopy Outline 3.1. Types of Atomic Spectroscopy – AES and AAS 3.2. Atomization process and different atomization methods (Flame, GF, ICP) 3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages...

Analytical Chemistry 3 – Atomic Spectroscopy Outline 3.1. Types of Atomic Spectroscopy – AES and AAS 3.2. Atomization process and different atomization methods (Flame, GF, ICP) 3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks 3.4. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks 3.5. Spectral interferences in AAS 3.6. Safety precautions 3.7. Detection limits for atomic spectroscopy Further Reading: Fundamentals of Analytical Chemistry, 9th edition, D. A. Skoog et. al. pages 773- 799 Prepared By: Analytical Chemistry Team 2022 2  3.1. Types of Atomic Spectroscopy – AES and AAS Types of Atomic Spectroscopy Atomic Atomic Emission Absorption Spectrometry Spectrometry (AES) (AAS) Atomic spectroscopy methods are categorized based on the type of atomization. Atomization = a process by which molecular constituents (analyte) of a sample are and converted to atoms (and ions) in the gaseous state. The atomization process is the “signal generator”. pages 773- 775 01/04/2025 Prepared By: Analytical Chemistry Team 2022 3  3.1. Types of Atomic Spectroscopy – AES and AAS tors contribute to atomic spectral line widths 1. Natural Broadening 2. Collisional Broadening 3. Doppler Broadening Partial absorption spectrum for Electronic transitions responsible sodium vapor. for the absorption lines in (a) pages 773- 775 01/04/2025 Prepared By: Analytical Chemistry Team 2022 4  3.2. Atomization process and different atomization methods (Flame, GF, ICP) Atomization Process nebulization desolvation vaporization [M+,X-]aq [M+,X-]aq [MX]solid [MX]gas solution mist atomization n io at iz om excitation at or emission absorption [M0]gas [M*]gas (via heat or [M0]gas [X0]gas ground state excited state light) [M+]gas [X+]gas pages 776- 777 The details of the process is explained in the book please check the references in last slide  3.2. Atomization process and different atomization methods (Flame, GF, ICP) Atomization Spectroscopic Methods Flame Graphite Furnace (GF) or Electro-thermal Atomizer ICP (inductively coupled plasma) Prepared By: Analytical Chemistry Team 2022 6  3.2. Atomization process and different atomization methods (Flame, GF, ICP) tomization Spectroscopic Method: Flame  A range in atomization temperatures can be achieved by changing and varying the fuel/oxidant mixtures. pages 776- 777 01/04/2025 Prepared By: Analytical Chemistry Team 2022 7  3.2. Atomization process and different atomization methods (Flame, GF, ICP) Process in flame 3- Atoms and ions are dispersed into 3.Outer cone the atmosphere. ( secondary 4- Oxidation may take place before the combustion dispersion. zone) 2.Inner cone 2- Solid particles are carried by the (interzonal air-fuel velocity: atomization, region) excitation and relaxation take place. 1.Base region (primary 1- Solvent evaporates leaving the combustion fine solid particles behind. zone) 1 pages 786- 788  3.2. Atomization process and different atomization methods (Flame, GF, ICP) omization Spectroscopic Method: GF The atomization process is achieved and temperature is rigorously controlled using a series of heating steps. Atomization Typically 10-50 µL. 3 Enhanced sensitivity over flame atomization. The entire sample is analyzed 2 Much of the background matrix can be eliminated Remove water 1 Destroy organics pages 778- 781  3.2. Atomization process and different atomization methods (Flame, GF, ICP) omization Spectroscopic Method: ICP The atomization process is achieved by using plasma (about 6000 K) 3 - There is atomization, ionization and a more intense emission compared 3 to flame. 2 The ions couple with the magnetic field. The interaction of the magnetic field causes atoms and ions to undergo extreme resistive heating. 1 2 - They are passed through an induced magnetic field 1 - A stream of partially ionized argon gas pages 778- mixed with nebulized sample solution 781  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Atomic Emission Spectroscopy (AES) Prepared By: Analytical Chemistry Team 2022 11  3.5. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks ame Atomic Emission Spectroscopy What is atomic emission?  Rapid relaxation of excited species is accompanied by emitting of ultraviolet and visible light at discrete wavelengths (line spectra)  The emission of light from atoms is measured.  The intensity is proportional to the concentration of atoms in pages 786- 788 the particular excited state  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks ame Atomic Emission Spectroscopy Stages of flame emission spectroscopy 1 Evaporation sample dehydration by heat & solvent evaporation 2 Atomization metal ions are reduced to metal atoms 3 Excitation Electrons of metal atoms absorb energy from the heat of the flame 4 Emission of radiation pages 786- Electrons in the excited state move back down 788 to the ground state and emit the absorbed energy  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Flame Atomic Emission Spectroscopy: Instrumentation 2- Source 3 4 5 pages 786- 788 1- Sample 1. Sample 3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks container Sample solutions are aspirated from an external container (beaker) A nebulizer 2- a side arm, at convert 1- a small plastic right angle to the solutions tube, used to suck plastic tube for the into a fine up the sample oxidant flow aerosol solution spray The rapid flow of the oxidant through the side arm creates suction in the sample tube called pages 786- Venturi effect. 788  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages 2. Flame and drawbacks 2.1.Turbulent Flow burners Flame Photometers are equipped with nebulizer + burner = single unit Advantages Introduces a relatively large and representative sample into the flame (sample flow rate ≈ 1 to 3 ml/min). Disadvantages (a) Short path length. Clogging of tip occurs frequently. (b) Noisy flame (c) Sample is nebulized at the tip, (on the burner head). Large sample droplets are not eliminated. Type of fuel used acetylene and air High Temperature pages 786- Low burning rate 788 (2300 K) 3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Prepared By: Analytical Chemistry Team 2022  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks 2.2. Premix (Laminar Flow) burner Pre-mix Advantages  Long sample path length (5-10 cm). NO problem of clogging.  Quiet flame.  Sample is nebulized by oxidant before reaching the burner head. Large sample droplets are drained out at the mixing chamber. Disadvantages Lower rate of sample introduction. This reduces the chance of introducing a representative sample into the flame pages 790- 795 3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Premix (Laminar Flow) burner  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks 3. Wavelength Selector To isolate a narrow wavelength band from the continuous wavelength of the electromagnetic spectrum Bandwidth is the section of the band Filters are used for wavelength that is allowed to selection pass through Filters are colored glasses allow absorption in the visible region only pages 786- The narrowness of the bandwidth the high 788 resolution is obtained  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks 4. Detector Light sensors such as photomultiplier tubes or photodiodes pages 786- 788  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Flame Atomic Emission Spectroscopy: Instrumentation pages 786- 788  3.3. Atomic Emission Spectroscopy – Flame AES instrumentation, advantages and drawbacks Advantages of flame photometry simple Instrumentation cheap sensitive Less maintenance Drawback Limited application pages 786- 788  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Atomic Absorption Spectroscopy (AAS) Prepared By: Analytical Chemistry Team 2022  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks AAS – Basic Components  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Source of Radiation in AAS Hollow Electrodeles Cathode s Discharge Lamps (HCL) Lamps )EDL) 26  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks ollow Cathode Lamps (HCL) Exit window composed of pyrex or quartz; depending on wavelength produced Filled with an inert gas (Ne or Ar) at low Lamps receive vacuum (1-5 an applied torr) potential of ~ pages 790- 795 300 V DC  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks An applied potential of ~ 300 V DC ionizes the inert gas Ar (g) -----> Ar+* (g) + e- positively charged Ar+ collide with the metal cathode e.g. Fe, Mn, Ca The solid metal atoms Some of the sputtered cations sputtered from are in excited states (M*) the cathode & changed to and emit light (hn) as they gaseous metal atoms return to ground state (M0) M (s) -------> M (g) M* -----> M0 + hn  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks HCL Light Intensity Limitation sputtered cations redeposit; this occurs mostly on the cathode, but some also deposit on the inner glass surface Light intensity limitation –> self absorption As the current increases, M sputtered increases, but the % M* decreases. Unexcited gaseous atoms (M0) absorb light produced within the lamp, preventing it from exiting the lamp. pages 790- 795  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Electrodeless Discharge Lamps A radio frequency (or microwave) The quartz tube coil surrounds the lamp is under high vacuum a sealed quartz tube (lamp) containing argon gas & a metal /metal salt of interest Characteristics: ~ 10 times MORE intense than a hollow cathode lamp Unstable output pages 790- ONLY available for about 17 metals 795 3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Ar M Ar* Ar* M* M Collision EMITION Argon gas Energy Intense RF transferred M* Return Argon=Ioniz to ground ed + gains state M IONIZATIO kinetic EXCITATIO Emit light N energy N Ar ---------> Ar* (g) (g) + M (s) -------> M* (g) + Ar (g) Hn pages 790- M (s) 795  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Chopper and background correction pages 790- 795 Prepared By: Analytical Chemistry Team 2022  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Wavelength Selector  placed between the flame and the detector  It filters out flame emissions and light from the room, so that ONLY radiation from the light source reaches the detector.  Monochromators are usually used for wavelength selection  To select wavelengths in both the UV and visible regions of the spectrum of pages 790- 795 Prepared By: Analytical Chemistry Team 2022  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Wavelength Selector  Monochromators Made up of three1-parts: (B) an entrance slit 2- (D) a dispersing element to splits the electromagnetic radiation into its constituent wavelengths e.g. a prism or a diffraction grating) pages 790- 795 3-(F) an exit slit  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Detector Photodiodes or photo-multipliers. Attached to an amplifier and an analog or digital readout device. pages 790- 795 Prepared By: Analytical Chemistry Team 2022  3.5. Atomic Absorption Spectroscopy – instrumentation, advantages and drawbacks Advantages (a) Used for the determination of over 60 elements (b) Suitable for routine analysis because measurements are fast (c) Hardly any clogging problem, therefore down time is very much reduced. Drawback Amount of sample enters the flame is relatively smaller than in Flame Photometry, therefore it is NOT as sensitive pages 790- 795  3.5. Types of interferences in Atomic Spectroscopy Types in Atomic Spectroscopy Analyte Interferences Blank Interferences: Physical spectral Chemical ionization pages 788- 789  3.5. Types of interferences in Types of analyte Atomic Spectroscopy Interferences in AES Chemical Spectral species in the sample when the absorption or matrix interfere with the emission spectra of an atomization of the interfering species analyte overlaps or lies close to Enhances or decreases that of the analyte. the volatility of the analyte Physical When the viscosity of the Ionization sample change(due to Present of easy ionized present of some element in the sample substance) to alter flow (e.g K) alter the less easy rate & nebulization ionized element (e.g Ca) efficiency pages 788- 789  3.5. Types of interferences in Atomic Spectroscopy Example of Spectral Interferences Determination of Ba in the presence of Ca pages 788-789 39 Prepared By: Analytical Chemistry Team 2022  3.5. Types of interferences in Atomic Spectroscopy Both Ca and Ba atomize simultaneously Ca (g) + oxidant -- >CaOH (g) CaOH (g) exhibits broad band molecular absorption The observed λBa λBa absorbance is in error Signal Signal due to the non-atomic Non-atomic signal signal coming from CaOH (g) pages 788- Wavelength Wavelength 789  Solutions for Spectral 3.5. Types of interferences in Atomic Spectroscopy Interferences oxidant/fuel mixture A Standards – A blank Source of correctio combustion n products Use hotter sample flame matrix e.g N2O- pages 788- acetylene flame 789  3.5. Types of interferences in Atomic Spectroscopy Chemical Interferences in Most chemical interferences result from a change in the atomization behavior of the analyte Usually the atomization signal is depressed The interference usually comes from analysis of an analyte in low concentration in a complex matrix (e.g. seawater) pages 788- 789 Prepared By: Analytical Chemistry Team 2022 Example of Chemical Interferences 3.5. Types of interferences in Atomic Spectroscopy Determination of Calcium in the presence of phosphate  An equilibrium exists in aqueous solutions between calcium and calcium phosphate Ca2+ + PO4-3 CaPO4-1 less volatile (more difficult to atomize) than Ca2+  as [PO4-3] increases, [CaPO4-1] increases and [Ca2+] decreases The absorbance of atomic calcium decreases as pages 788- phosphate content in the sample increases 789  3.5. Types of interferences in Solutions Atomic Spectroscopy for Chemical Interferen ces C. A. Protective Hotter agents B. flames Releasing forms stable but volatile agents compounds with analyte ions. reacts preferentially with the interfering e.g. EDTA anions pages 788- Strontium and lanthanum reacts with PO4-3, 789 preventing it from interfering during Ca determination.  Ionization interferences 3.5. Types of interferences in Atomic Spectroscopy Present of easy ionized(lower Solutions ionization energy) elementfor in the sample alkali Chemical and alkaline earth metal (e.g Interferences K) alter the less easy ionized element (e.g Ca) Solution pages 788- 789 ASAC2313 WAR 2010  Safety Precautions 3.6. Safety precautions Acetylene gas is highly flammable, therefore, gas cylinders must be - immovable - should be secured to a wall. - Standard pressure regulators should be firmly attached to these cylinders. - All tubings and connectors must be free of gas leaks. - Carts should be used to transport the cylinders rather than rolling them on the floor. There must be a vent fume hood placed above the flame to remove toxic combustion products. Volatile flammable organic solvents such as ether and acetone must not be kept near the bench where the instrument is. The nebulizer should be cleaned periodically to remove carbon deposits and other impurities to reduces flame noise. Gas flow regulators must be in good working conditions to avoid flashbacks resulting from improperly mixed fuel and air.  3.7. Detection limits for atomic Detection Limits for Atomic spectroscopy Spectroscopy Trend: ICP-MS > GFAAS > ICP-AES > page 796 FAAS > FAES More details are available in the book please check the references in last slide References Skoog, D.A., West, D.M., Holler, F.J., and Crouch, S.R. (2014) Fundamentals of Analytical Chemistry, 9th ed. USA: Brooks/Cole, Cencage Learning. Christian, G. D. (2003). Analytical Chemistry, 6th ed. USA: John Wiley & Sons. Harris, D.C. (2007) Quantitative Chemical Analysis, 7th ed. USA: W.H. Freeman and Company Dean, J.R., Jones. A.M., Homes, D., Reed, R., Wyers, J. and Jones, A. (2002) Practical Skills in Chemistry. Great Britain: Ashford Colour Press Gosport, Hants. 48 Prepared By: Analytical Chemistry Team 2022