hot gaseous cload of atoms, ions and electrons - neutral overall - no combustion - 5000-10000K

1. Easily ionisable 2. Background 3. Dominant Matrix 4. Wavelength coincidence 5. Chemical

ICP2 Flashcards by Patrick B

AES details

atoms excited causing photon emission

wavelength characteristic of element

intensity proportional to concentration

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Plasma Details

hot gaseous cload of atoms, ions and electrons

neutral overall
no combustion
5000-10000K

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Direct Current Plasma Details

High voltage between 3 electrodes ionises gas creating plasma

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DCP advantages

economical

sample tolerance esp liquids

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DCP cons

Sample doesn’t reach hottest parts (5000K)

unreliable

electrodes consumed

interference from electrodes

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Microwave induced plasma details

microwave radiation heats gas to plasma

2000K

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MIP pros

can run on N2

inexpensive

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MIP cons

low temps

severe matrix effects (from low temps)

easily extinguished

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ICP Torch

3 concentric tubes encapsulated by RF coil

~8000K

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ICP process

RF coil creates rapidly oscillating field in torch

charged ions/e- become energetic creating collisions

collisions generate heat creating plasma

seed ions needed initially but thereafter inductively heated

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ICP pros

instantly responsive

very high temps

reproducible

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ICP cons

consumes a lot of Ar

only 2% of sample reaches plasma

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Plasma process

solvent vaporisation

melting and Vaporisation of analytes

fragmentation

atomisation

ionisation and excitation

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Advantages of Plasma over flame

higher temps mean simultaneous multielemental analysis (5-10000K vs 1500K)
more elements excited
higher proportion excited so higher sensitivity
reduced cool zone and interferences
simpler spectra
MS
refractory compounds analysis
non metals
linear calibration over wider range
greater control and reproducibility

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ICP AES spectrometers pros cons

Sequential e.g. photonmultiplier tube

more sensitive
better signal to noise
slower

Simultaneous e.g. CCD

fast
higher noise

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AES spectrometer orientation

Radial - side on

smaller cool zone
shorter path length

Axial - end on

larger cool zone
longer path length, more sensitive
needs better spectrometer

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AES Interferences

Easily ionisable
Background
Dominant Matrix
Wavelength coincidence
Chemical

Correcting AES interferences

higher temperatures

matrix matching

standard addition

standards

remove interferring

preconcentrate

observe different wavelength

ICP MS parts

sample introduction
ICP torch
MS interface
Mass separator
detector

MS process

sample introduced

ionised in plasma

ions drawn through cone by voltage

pumps at interface keep MS under vacuum

ions separated by MS

ions collide with detector and measured as current

Mass Spectrometers

Quadrupole

Magnetic sector

double focussing MS

Quadrupole details

4 rods of alternating polarity

magnetic field controlled to allow only one m/z to reach detector rest deflected

Quadrupole pros and cons

fast simple cheap

only unit resolution

Magnetic Sector Details

ion beam is curved by magnet

extent ions curve determined by m/z

select m/z by altering magnetic field and accelerating voltage

Magnetic Sector pros and cons

Higher resolution limited by energy distribution of ions expensive

Double Focussing MS details

electrostatic analyser focusses ion energies allowing for higher resolution

Double focussing MS pros and cons

highest resolution less interferences most expensive

MS detectors

Electron multiplier electron channel multiplier

MS spectro interferences

1. isobaric overlap - isotopes of same mass 54 Fe Cr 2. polyatomics - mainly argon adducts e.g. 80ArAr and Se 3. multicharged e.g Cu+ and Ba2+

MS spectro interference solutions

observe different isotope use higher res use isotope abundances to subtract interference use common element acids e.g. HNO3 desolvate/ remove solvent remove interferring e.g. collision/reaction cell

MS Matrix interferences

Easily ionisable High Conc - greater variation, non-reproducible, memory effects Carbon deposition - blocked cones reduce sensitivity

MS Matrix interferences solutions

Dilution Matrix matching standard addition internal standard chemically remove isotope dilution

Collision Cell details

polyatomics are larger thus collide more, lose more energy. energy barrier then removes simply

Reaction Cell

Contains reactive gas e.g. CH4, NH3 reacts selectively with polyatomics converting them to uncharged non-interferring species e.g. 56ArO+ + NH3 -\> O + Ar + NH3+

Triple Quad

Quad MS mass shift reaction cell Quad MS

Benefits of MS and con

Multielemental isotope analysis mos elements interference free fast low detection limits large linear calibration range only 2% of sample reaches plasma

Liquid sample intro

1. Nebulise - creates fine mist to prevent extinguishing pneumatic or ultrasonic (better) 2. spray chamber - removes large droplets makes homogeneous

Gas Intro and pros

Some metals form volatile hydrides can thus be readily extracted from matrix e.g, M^m+ + (m+n)H -\> MH_n+ MH⁺ preconcentrated more efficient than nebuliser selective

Solid Intro

Electrothermal Vaporisation e.g polymers Laser ablation e.g. rocks - targetted

ICP quantification

External standards - compare intensity against known conc results Standard Addition - add known amount of standard to sample to create calibration curve and work backwards to original (better as eliminated matrix differences) internal standard - for checking matrix of external standards

Electrothermal Vaporisation pros and cons and analytes

polymers pro good detection limit con homogeneous sample conducting sample decompose sample

Laser Ablation Details, analytes, pros and cons

higher energy sputters surface molecules into vapor rocks or anything pros targetted non conducting different scan modes cons can decompose sample