Atomic Spectroscopy Flashcards by Ray Mark

Types of Atomic Spectroscopy (3)

Atomic Absorption Spectroscopy
Atomic Emission Spectroscopy
Atomic Fluorescence Spectroscopy

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Basic Instrumentation of Atomic Absorption Spectroscopy

Radiation Source > Focusing Lens > Atomizer and Sample > Focusing Lens > Wavelength Selector > Detector > Amplifier > Signal Processor

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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

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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-

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Using Hollow Cathode Lamp, ionized Ar+ strikes that cathode with sufficient energy to ____ and _____

dislodge and excite some of metal atoms

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In using Hollow Cathode Lamp, excited metal atoms emit their _____ as they return to ground state

characteristic wavelengths

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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

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In electrodeless discharge lamp, a ____ or _____ generates intense RF field, causing the ionization of Ar

coil of radiofrequency (RF) or microwave radiation

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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

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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

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Radiation source that can emits continuous spectrum at high intensity and all the elements can be measured from 185-900 nm

xenon arc lamp

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High intensity Xe lamp gives ___ and ____

better signal/noise ratio and detection limit

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Atomization process that involves reduction to a fine spray by passing the solution through thin nozzle

nebulization

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Atomization process that involves removal of solvent, leaving just the analyte and other matrix compounds

desolvation

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Atomization process that involves converting solid analyte/matrix into gas phase

volatilization

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Atomization process that involves break-up molecules into atoms

dissociation

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Atomization process that involves light, heat, etc. for spectra measurement

excitation

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Atomization process that causes atom to become charged

ionization

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Sample -?-> mist -?-> solid/gas aerosol -?-> gaseous molecules -?-> atoms

Sample —nebulization—> mist —desolvation—> solid/gas aerosol —volatilization—> gaseous molecules —dissociation—> atoms

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In flame atomization method, ideal flow rate is ____

flow velocity +burning velocity

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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

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In flame optimization, the maximum temperature is located _____

above the primary combustion zone

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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

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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)

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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)

1. Easy to use 2. Very fast 3. Lowest capital cost 4. Relatively few interference 5. Very compact instrument 6. Good performance 7. Robust interface

Limitations of FAAS (4)

1. Moderate detection limits 2. Element limitations 3. 1-10 elements per determination 4. 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

1. Dry: a fixed temperature and times is used to remove solvent (50-200 C) 2. Ash: a second temperature used to decompose the matrix (200-800 C) 3. Atomization: a rapid increase tot 2000-3000 C for just a few seconds

Strengths of GFAAS (5)

1. Very good detection limits 2. Small sample size 3. Moderate price 4. Very compact instrument 5. Few spectral interferences

Limitations of GFAAS (6)

1. Slower analysis time 2. Chemical interferences 3. Element limitations 4. 1-6 elements per determination 5. No screening ability 6. 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)

1. Wet Ashing 2. Dry Ashing 3. Fusion 4. Solubilization 5. 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)

1. Use higher temperature flame 2. Use of releasing agent 3. Use of protection agents

Spectral lines that occur at different λ than atomic lines

ionization interference

Causes of ionization interference (3)

1. decrease in AAS signal 2. ionization decrease at high concentration 3. competition between atoms for available energy

Remedy for ionization interference (3)

1. Use of low temperature flame 2. Use of high concentration of analyte 3. Use of ionization suppressor

Caused by the physical nature of matrix enhancing or depressing sensitivity

matrix interference

Remedy for matrix interference (3)

1. Use of standard addition technique 2. Use of solvent extraction to isolate the analyte 3. Use of radiation buffer

interference with overlapping of spectra (analyte and matrix absorb at the same wavelength)

spectral interference

Remedy for spectral interference (3)

1. Chemical separation prior to analysis 2. Modulation of the detector 3. 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)

1. Flame 2. Plasma 3. Electrothermal 4. Laser Ablation 5. Spark or arc ablation 6. 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)

1. Inductively coupled Plasma (ICP) 2. Microwave-induced plasma (MIP) 3. Direct current plasma (DCP) 4. Laser-induced Plasma

Atomization method for solution (2)

1. pneumatic nebulization (solution or slurry) 2. 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)

1. direct insertion 2. laser ablation

Atomization method for conducting solid (2)

1. spark or arc ablation 2. 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