ICP2 Flashcards
AES details
atoms excited causing photon emission
wavelength characteristic of element
intensity proportional to concentration
Plasma Details
hot gaseous cload of atoms, ions and electrons
- neutral overall
- no combustion
- 5000-10000K
Direct Current Plasma Details
High voltage between 3 electrodes ionises gas creating plasma
DCP advantages
economical
sample tolerance esp liquids
DCP cons
Sample doesn’t reach hottest parts (5000K)
unreliable
electrodes consumed
interference from electrodes
Microwave induced plasma details
microwave radiation heats gas to plasma
2000K
MIP pros
can run on N2
inexpensive
MIP cons
low temps
severe matrix effects (from low temps)
easily extinguished
ICP Torch
3 concentric tubes encapsulated by RF coil
~8000K
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
ICP pros
instantly responsive
very high temps
reproducible
ICP cons
consumes a lot of Ar
only 2% of sample reaches plasma
Plasma process
solvent vaporisation
melting and Vaporisation of analytes
fragmentation
atomisation
ionisation and excitation
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
ICP AES spectrometers pros cons
Sequential e.g. photonmultiplier tube
- more sensitive
- better signal to noise
- slower
Simultaneous e.g. CCD
- fast
- higher noise
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
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
- isobaric overlap - isotopes of same mass 54 Fe Cr
- polyatomics - mainly argon adducts e.g. 80ArAr and Se
- 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
- Nebulise - creates fine mist to prevent extinguishing
pneumatic or ultrasonic (better)
- 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, Mm+ + (m+n)H -> MHn + 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
