What are the three main types of atomic spectroscopy mentioned?
Atomic Absorption Spectroscopy (AAS), Atomic Fluorescence Spectroscopy (AFS), and Atomic Emission Spectroscopy (AES).
What fundamental transition is involved in AAS, AFS, and AES?
The transition of outer electrons of an element.
What is the primary purpose of sample-introduction methods in atomic spectroscopy?
To transfer a reproducible and representative portion of a sample into the atomizer with high efficiency and no adverse interference effects.
What are the four complex processes that occur during flame atomization
1) Desolvation (solvent evaporates to leave solid aerosol).
2) Volatilization (solid aerosol turns to gas).
3) Dissociation (molecules break into free atoms).
4) Ionization (atoms lose electrons to form ions).
Definition: Direct Nebulization
Direct nebulization in instrumental analysis is a technique where a liquid sample is converted directly into a fine aerosol (mist) for introduction into an instrument,
What is the main advantage of an ultrasonic nebulizer over a pneumatic one?
It produces a more dense and more homogeneous aerosol, leading to higher efficiency.
How does a pneumatic nebulizer work?
It uses a high-velocity stream of gas to break up a liquid sample into small droplets. This process often aspirates (draws up) the liquid using the Bernoulli effect.
Definition: Electrothermal Atomizer (Graphite Furnace)
A device that uses electrical resistance heating to rapidly raise the temperature of a small graphite tube, converting a micro-volume of liquid sample into free gaseous atoms.
Mechanism
1) A few (µL) of the sample is placed on a graphite furnace
2) the graphite furnace is heated to a low temp and the solvent evaporates leaving behind aerosols
3) The temp is increased to an intermediate temperature and the aerosols ashed onto the furnace
4) The current is increaaed to several hundreds if ampere, which caused the temp to increase around 2000-3000°C and the sample atomizes and is carried away by the gas
Why is an electrothermal atomizer more sensitive than a flame atomizer?
The electrothermal atomizer is a more efficient atomizer. It requires much less sample and keeps the atomic vapor in the beam for a longer time than does a flame.
Residence Time in Optical Path:
- In a flame atomizer, the atoms travel through the optical path very quickly (on the order of milliseconds) before dispersing.
- In an electrothermal atomizer, the atoms are confined within a small graphite tube, and the average residence time in the optical path is increased to a second or more. This allows the detector to measure the signal from each atom for a longer duration.
Total Sample Atomization:
- During flame atomization, a solution is nebulized, and a large portion of the sample is often lost to drainage before reaching the flame.
- Conversely, in electrothermal atomization, the entire sample (typically a micro-volume) is placed in the tube and atomized in a short period, ensuring every atom present in the sample can contribute to the measurement.
Lower Detection Limits: These physical advantages result in detection limits that are often 10 to 100 times better than those of flame atomic absorption.
Calculate the energy of the average wavelength of 589.3nm for the two sodium emission lines corresponding to the
“3 p->3 s transitions”
What are the three heating stages in an electrothermal atomizer?
1) Drying (evaporation at low temp).
=>A few µL of sample is first evaporated at a low temperature,
2) Ashing (removal of matrix at intermediate temp).
=>in an electrically heated graphite tube.
3) Atomization (rapid heating to 2000-3000°C to create atomic vapor).
Additional info
4) The absorption of the atomic vapor is then measured in the region immediately above the heated surface.
What is the function of the L’vov platform in a graphite furnace?
It delays atomization until the furnace wall temperature stabilizes, ensuring atomization occurs in a more constant, isothermal environment for better reproducibility.
Definition: Hydride Generation
Introducing samples containing Arsenic (As), Antimony (Sb), Tin (Sn), Selenium (Se), Bismuth (Bi), and Lead (Pb) into an atomizer as a gas.
How it works
1) Volatile hydrides are generated by adding an acidified aqueous solution of the sample to a small volume of a 1% aqueous solution of sodium brorhydride.
2) the volatile hydride is then swept into the atomization chamber by and inert gass. (The atomization chamber is heated to several hundred degrees) .
3) Decomposition of the hydride takes place in the atmization chamber
Definition: Glow-Discharge Atomization
A method where argon ions accelerated by an electric field bombard a solid sample (cathode), ejecting atoms through a process called sputtering.
Glow discharge device preforms both sample introduction and sample atomization.
Glow discharge occurs in a low-pressure of argon gas between a pair of electrodes maintained at a dc voltage of 250 to 1000 V.
1) The applied voltage causes the argon gas to ionized to Ar+ ion and e-
2) The electric field accelerates the Ar+ ions to the cathode surface (that contains the sample).
3) Neutral sample atoms are ejected from the cathode surface by a sputtering process.
The atomic vapor produced in a glow discharge consists of a mixture of atoms and ions that can be determined
by atomic absorption or fluorescence or by mass spectrometry.
And a fraction of the atomized species in the vapor is in an excited state, when they return to their ground state they produce a low intensity glow => this can be used for optical measurements
What is sputtering
Like for the Hollow cathode lamp, A sputtering process is when an inert atmosphere is created in a chamber, an inert gas is then introduced (often argon). Then a high volatage is applied between the electrodes and ionizing the argon gas: where the cations will migrate to the cathode and the free electrons migrates to the anode.
when the cations migrate to the cathode surface, thus will lead to the ejection (or sputtering) of atoms of the cathode metal layer. The atoms is ejected into the argon gas.
Why are Hollow-Cathode Lamps (HCLs) used as sources for AAS?
Because they emit extremely narrow, characteristic lines of the analyte element, which are necessary to effectively measure the very narrow atomic absorption lines and obey Beer’s Law.
“Explain why the use of a wide-bandwidth monochromator and a continuum light source in AAS results in poor sensitivity and a failure to obey Beer’s Law (non-linear calibration curve).”
The instrument’s bandwidth is much wider than the atomic absorption line. This leads to a very small fraction of light being absorbed (poor sensitivity) and a non-linear calibration curve (failure of Beer’s Law).
How does temperature affect the ratio of excited to ground-state atoms (Boltzmann Equation)?
Higher temperatures exponentially increase the population of excited atoms ($N_j/N_0$). This makes Atomic Emission highly temperature-sensitive.
Why is Atomic Absorption (AAS) less sensitive to temperature fluctuations than Atomic Emission (AES)?
AAS measures the ground-state population (approx. 99.98%), which changes negligibly with temperature. AES measures the tiny excited population, which changes drastically.
What is the ‘Doppler Effect’ in the context of line broadening?
The broadening of spectral lines caused by the rapid thermal motion of atoms. Atoms moving toward the detector absorb/emit higher frequencies; those moving away absorb/emit lower frequencies.
In a flame, which zone is typically used for spectroscopy and why?
The Interzonal Region. It is rich in free atoms and has the most uniform temperature, making it ideal for absorption and emission measurements.
What is the main advantage of Cold-Vapor Atomization?
It is the only method for determining Mercury (Hg), as it is the only metal with a significant vapor pressure at ambient temperature.
What is the difference between continuous and discrete atomizers?
and give expamples of continuos and discrete atomizers
Continuous: Sample is introduced steadily (e.g., Flame, Plasma).
Discrete: Sample is introduced in a discontinuous pulse (e.g., Electrothermal/Graphite Furnace), producing a transient signal.
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Chp. 3 OP amps28
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Signal and Noise Chp. 523
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Figures of merit Chp. 19
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Intro Spec Chp. 610
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Chp. 78
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Chp. 2 Electrical cicuits21
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Intro to optical atomic spec Cph. 852
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Chp.950
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Chp. 7 Components of Optical Instruments: FT21
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Chp. 10 Atomic emission spec28
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Assignments31
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Chp. 11 Mass spectroscopy43
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Chp. 12 X-ray spectroscopy25
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Chp. 13 + 14 UV-VIS and its applications44
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Chp. 15 Fluorescence and phosphor28
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Chp. 16 +17 IR + applications0
