Atomic Spectroscopy Flashcards
Types of Atomic Spectroscopy (3)
- Atomic Absorption Spectroscopy
- Atomic Emission Spectroscopy
- Atomic Fluorescence Spectroscopy
Basic Instrumentation of Atomic Absorption Spectroscopy
Radiation Source > Focusing Lens > Atomizer and Sample > Focusing Lens > Wavelength Selector > Detector > Amplifier > Signal Processor
Radiation source that consists of a tungsten anode and a cylindrical cathode sealed in a glass tube containing an inert gas (e.g., Ar)
Hollow Cathode Lamp
Using Hollow Cathode Lamp, the cathode is fabricated from the analyte metal or serves as
_____ of that metal application of a potential of about +300 V across the electrodes causes ionization of ____ to ____
a support for coating
Ar to Ar+ & e-
Using Hollow Cathode Lamp, ionized Ar+ strikes that cathode with sufficient energy to ____ and _____
dislodge and excite some of metal atoms
In using Hollow Cathode Lamp, excited metal atoms emit their _____ as they return to ground state
characteristic wavelengths
Radiation source that has a lamp constructed from a sealed quartz tube, containing an inert gas (ex. Ar) at a pressure of few torr and a small quantity of the analyte metal (or its salt)
Electrodeless Discharge Lamp
In electrodeless discharge lamp, a ____ or _____ generates intense RF field, causing the ionization of Ar
coil of radiofrequency (RF) or microwave radiation
In electrodeless discharge lamp, the ions (ionized Ar) are accelerated by the RF field, thereby ______, whose emission spectrum is sought
colliding with and exciting the atoms of the metal
Radiation source where electric arc between two electrodes causes excitation of xenon filled in a quartz tube and xenon atoms/atoms upon deexcitation gives continuous spectrum
Xenon arc lamp
Radiation source that can emits continuous spectrum at high intensity and all the elements can be measured from 185-900 nm
xenon arc lamp
High intensity Xe lamp gives ___ and ____
better signal/noise ratio and detection limit
Atomization process that involves reduction to a fine spray by passing the solution through thin nozzle
nebulization
Atomization process that involves removal of solvent, leaving just the analyte and other matrix compounds
desolvation
Atomization process that involves converting solid analyte/matrix into gas phase
volatilization
Atomization process that involves break-up molecules into atoms
dissociation
Atomization process that involves light, heat, etc. for spectra measurement
excitation
Atomization process that causes atom to become charged
ionization
Sample -?-> mist -?-> solid/gas aerosol -?-> gaseous molecules -?-> atoms
Sample —nebulization—> mist —desolvation—> solid/gas aerosol —volatilization—> gaseous molecules —dissociation—> atoms
In flame atomization method, ideal flow rate is ____
flow velocity +burning velocity
In flame atomization method,
Too high flow rate = ____
Too low flow rate = _____
Too high flow rate = flame blows off
Too low flow rate = flashback occurs
In flame optimization, the maximum temperature is located _____
above the primary combustion zone
In flame optimization, beam from lamp has to be focused on the part of the flame where _____
As this is different for elements, the ____ has to be adjusted while aspirating a standard solution of the analyte
atomization efficiency of the analyte is greatest
burner height
In flame optimization, increasing the angle ____ the path length of the light beam through the flame and ___ the absorbance
This can be useful for the analysis of concentrated solutions which may give off-scale absorbance reading when _____ is use
shortens the path length
decreases the absorbance
a maximum path length (zero burner angle)
In flame optimization, the initial increase in absorbance as the _____ increases due to the longer exposure to the heat causing more _____ atoms to be formed
distance from the flame base
magnesium atoms
In flame optimization using magnesium, absorption _____ if the magnesium is exposed even longer because ______
decreases
oxides are formed which absorbs at a different wavelength
In flame optimization using ____, no stable oxides so a continuous increase in absorbance is seen
silver
In flame optimization using ____, forms very stable oxides so there is a continuous decrease in absorbance as it rises above the burner tip
chromium
Type of burner which draws sample up and nebulizes by Venturi action
Turbulent Flow Burner
Turbulent flow burner consumes ____ amount of sample but with ____ path length, ____ problems, and ____
large amount of sample
short path length
clogging problems
noisy
Type of burner in which the sample is nebulized by flow of oxidant past a capillary tip
laminar flow burner
Using Laminar Flow Burner, the resulting aerosol is mixed with fuel and flows past a series of baffles that remove _____
The ___, ____, and ___ are fed into the burner
remove all but finest droplets
aerosol, oxidant, and fuel
Laminar Flow Burner has ___ drop size, ___ and ___ flame, and _____ path length,
but has ____ if Vburning>Vflow, ～____% of sample is lost, and ____ mixing volume
uniform drop size, homogenous and quiet flame, and long path length
flashback if Vburning>Vflow, ～90% of sample is lost, and large mixing volume
Meaning of the ff. acronyms:
FAAS
GFAAS
CVAA
Flame Atomic Absorption Spectroscopy
Graphite Furnace Atomic Absorption Spectroscopy
Cold-Vapor Atomic Absorption
Strengths of FAAS (7)
- Easy to use
- Very fast
- Lowest capital cost
- Relatively few interference
- Very compact instrument
- Good performance
- Robust interface
Limitations of FAAS (4)
- Moderate detection limits
- Element limitations
- 1-10 elements per determination
- No screening ability
____ is often used as a purge gas to remove excess material during the dry and ash phases after atomization
Argon
External argon gas prevents _____ by reducing oxidation of the tube and provide a ____ during atomization since high temperature carbon will react with nitrogen to produce ____
Internal argon gas _____
tube destruction
protective blanket
cyanogen
circulates gaseous analyte
Three stages of sample preparation for graphite furnace
- Dry: a fixed temperature and times is used to remove solvent (50-200 C)
- Ash: a second temperature used to decompose the matrix (200-800 C)
- Atomization: a rapid increase tot 2000-3000 C for just a few seconds
Strengths of GFAAS (5)
- Very good detection limits
- Small sample size
- Moderate price
- Very compact instrument
- Few spectral interferences
Limitations of GFAAS (6)
- Slower analysis time
- Chemical interferences
- Element limitations
- 1-6 elements per determination
- No screening ability
- Limited dynamic range
It provides a method for introducing samples containing arsenic, antimony, tin, selenium, bismuth, and lead into an atomizer as a gas
Hydride generation
Volatile hydrides can be generated by addition of an ____ of a sample to a small volume of a 1% aqueous solution of ____
acidified aqueous solution
sodium borohydride (NaBH4)
The volatile hydride during hydride generation is swept into the atomization chamber by an ____ which enhances the ______ by a factor of 10 to 100.
inert gas
detection limits
Determining volatile hydride at ____ levels is quite important because several of these species are highly toxic
low concentration
Spectroscopy used for the determination of Hg
Cold-Vapor Atomic Absorption (CVAA) Spectroscopy
In CVAA Spectroscopy, sample solution is treated with a _____ such as ____ which converts mercury ions to metallic mercury
reducing agent such as Sn(II)
In CVAA Spectroscopy, the metallic mercury is then swept into a____ for absorption measurement
On the completion of the measurement, the mercury is flushed from the system by pumping the vapor through a ____
glass cell
mercury absorption solution (KMnO4)
Sample Preparation for Atomic Spectroscopy (5)
- Wet Ashing
- Dry Ashing
- Fusion
- Solubilization
- Microwave
performed in open reaction systems using Kjeldahl flask or autoclave using strongly oxidizing mineral acids (HNO3, HClO4, H2SO4)
wet ashing
sample is placed in crucible (Pt or fused silica) dried at 105-110 C then ashed between 400 8800 C using a muffle furnace; ash is then dissolved in a variety of acids or mixtures of acids
dry ashing
geological sample is mixed in a Pt crucible with a flux such as lithium metaborate, hashed in a furnace at 1000 C, then cooled to room temp dissolved in HNO3
fusion
biological sample is dissolved in quaternary ammonium hydroxide (tetramethylammonium hydroxide)
solubilization
sample is mixed with acid and placed in a sealed vessel within the microwave digestion system
microwave
Cations like LaCl3 from Ca, Mag, Sr that preferentially reacts with a species that would otherwise react with the analyte causing a chemical interference
Releasing agents
prevent interferences by forming stable and volatile products with the analyte (example: EDTA)
Protection agents
atoms that are more easily ionized than the analyte and provides a high concentration of electrons in the flame, thus suppress the ionization of the analyte
ionization suppressors
substance added in excess to both sample and standards which swamps the effect of the sample matrix on the analyte
radiation buffer
Result of any chemical process (formation of compounds of low volatility) which decreases or increases the absorption of analyte
chemical interference
Remedy for chemical interference (3)
- Use higher temperature flame
- Use of releasing agent
- Use of protection agents
Spectral lines that occur at different λ than atomic lines
ionization interference
Causes of ionization interference (3)
- decrease in AAS signal
- ionization decrease at high concentration
- competition between atoms for available energy
Remedy for ionization interference (3)
- Use of low temperature flame
- Use of high concentration of analyte
- Use of ionization suppressor
Caused by the physical nature of matrix enhancing or depressing sensitivity
matrix interference
Remedy for matrix interference (3)
- Use of standard addition technique
- Use of solvent extraction to isolate the analyte
- Use of radiation buffer
interference with overlapping of spectra (analyte and matrix absorb at the same wavelength)
spectral interference
Remedy for spectral interference (3)
- Chemical separation prior to analysis
- Modulation of the detector
- Background correction
Basic instrumentation of Atomic Emission Spectroscopy
Excitation source > Sample holder > Lens > Wavelength Selector > Detector
Sequential spectrometer- uses ____
Simultaneous spectrometer- uses ____
sequential = monochromator
simultaneous = polychromator
Sources of Excitation in Atomic Emission Spectroscopy (6)
- Flame
- Plasma
- Electrothermal
- Laser Ablation
- Spark or arc ablation
- glow-discharge sputtering
The same source of thermal energy used for atomization usually serves as the ____.
excitation source
_____ is an electrically conducting gaseous mixture containing enough cations and electrons to maintain the conductance
Plasma
Plasma Sources in Atomic Emission Spectroscopy (4)
- Inductively coupled Plasma (ICP)
- Microwave-induced plasma (MIP)
- Direct current plasma (DCP)
- Laser-induced Plasma
Atomization method for solution (2)
- pneumatic nebulization (solution or slurry)
- ultrasonic nebulization (solution)
Atomization method for solid, liquid or solution sample
electrochemical vaporization
Atomization method for solution of certain elements
hydride generation
Atomization method for solid and powder samples (2)
- direct insertion
- laser ablation
Atomization method for conducting solid (2)
- spark or arc ablation
- glow-discharge sputtering
In principle, line absorption should only affect a very unique wavelength but in reality, also _____ are absorbed called ___
slightly different wavelengths
line broadening
Line broadening because of uncertainties in the transition times
Uncertainty effect
Uncertainty effect results from the ____ principle postulated in 1927 by _____
uncertainty principle
Werner Heisenberg
Line broadening because of rapid movement of atoms; emitted or absorbed wavelength changes as a result of atom movement relative to detector
Doppler effect
Wavelength _____ if atom moves toward a photon detector
Wavelength _____ if atom moves away from a photon detector
Wavelength decreases if atom moves toward a photon detector
Wavelength increase if atom moves away from a photon detector
Line broadening due to collision between atoms of the same kind and with foreign atoms
Pressure effect
Pressure effect is ____ in high pressure conditions
worse
line broadening that affects the number of atoms in ground and excited state
temperature effect
Since temperature changes number of atoms in ground and excited state, ____ is needed
good temperature control
