ICP Flashcards
what does ICP stand for?
inductively coupled plasma
An ICP torch is a devicce that produces a plasma - which is a fireball of what?
atoms, ions and electrons interacting at very high energies with temp of up to 10000 K
what does exposing a sample to the high temp plasma do?
converts a very large proportion of its constituent atoms to an excited state
ICP-AES can identify and determine how many elements? and with what detection limits?
0, ppb
if a sample consists of more than metal, there will be multiple emissions - what is requied for this?
suitable polychromators and scanning monochromator to allow multi-element analysis
Why is emission spectrum more complex?
because emission can occur to other excited states
The fuel and oxidant of flame is replaced by what?
Ar
Powerful radio-frequency electrical current is applied to what?
Cu load coil
the rf current has an associated magnetic field with lines of force passing along what?
axis of a quartz tube places inside the coil
A spark is applied, which ionises what?
a few Ar atoms
What happens to the electrons which are formed?
they are rapidly accelerated to and fro in circular orbits by rapidly alternating electric field
What do the collisions cause the gas to do?
heat up to a high temp of 10000K forming plasma
In the plasma torch, outside flow is used as what?
coolant to prevent tube melting
what maintains the plasma in plasma torch?
auxiliary flow
What carries the nebulised sample?
central injector
a hole is punched through the plasma creating a doughnut shape by what?
injector gas flow
why is the nebuliser different in ICP than flame?
lower flow rate of carrier gas employed
Name the 3 types of nebuliser?
babington, crossed flow, meinhard
What is the difference between crossed bow nebuliser and nebuliser in AAS?
nebuliser in ICP has finer bores
what does the high speed Ar flowing past tip of capillary create?
a low pressure region into which solution is aspirated as an aerosol
What kind of sample is a babington nebuliser used for?
slurries and viscous liquids
The sample flows over spherical surface and is converted into what?
an aerosol as high speed of Ar is forced through tiny hole in surface
In Meinhard nebuliser, the sample is transported to tip via what?
Bermouli effect
The high velocity gas flowing around tip of tube does what?
breaks up liquid into fine drops then carried to plasma
The basic detection system for ICP-AES consists of 3 main components, the first of which are collimating lenses/mirrors. What is their purpose?
Focus emitted light through an entrance slit on to the diffraction grating which disperses the emitted light
what are the other components of ICP-AES detector?
means of separating individual wavelengths, photomultiplier tubes
what are the 2 main designs for detection commercially available?
similtaneous, sequential
What are the 2 simultaneous spectrometers called?
polychromator, spectrograph
a polychromator is an array of detectors each tuned to emission wavelength of an element - How many elements can it determine quantitiatively within 5 mins?
20
What is a stepper motor used for in polychromator?
used to move entrance slit to scan peaks
Polychromator can be used for rapid routine analysis, give 2 disadvantages to this technique
more expensive then sequential instruments and not as versatile
What kind of spectrometer does a spectrograph utilise?
echelle
What is a stepper motor used for in sequential spectrometers?
used to move grating or entrance slit and PMT
Sequential spectrometers utilise slew scanning - what is this?
Has two speeds of scan, first fast (slews) to wavelength near line of interest, then slower to scan across line in small steps
able to slew .. elements and record ………. in less than .. minutes
15, intensities, 5
What are 2 disadvantages to slew scanning?
Generally slow and consume more sample than multichannel instruments
sequential Uses scanning ……….. and single …………..
monochromator, photomultiplier
how is the monochromator scanned in sequential?
using a stepper motor under computer control
What does a scanning echelle operate as?
scanning or simultaneous multichannel instrument
What does aperture plate consist of in scanning echelle of sequential spectrometers?
consists of lots of slits corresponding to different elements spectral line
is scanning echelle able to run in slew scanning mode?
yes
How can scanning echelle be made multichannel?
if several PMTs are mounted behind appropriate slits in aperture plate
If an analysis was needed to be done on samples of various concentrations/elements rapidly, what spectrometer would you opt for?
similtaneous
If the sample type is relatively constant and speed of analysis is important, which system would be preferred?
polychromator
In a general lab, the monochromator system is the preferred system - why?
usually designed to scan in important 190-450nm region
What are 3 advantages of sequential?
cost, flexibility, and allows optimisation of parameters
What are 3 advantages of similtaneous?
speed, accuracy and precision since 1 channel can be set for IS
How can the spectral interference of adjacent atomic lines overlapping be avoided? 2
applying correction for other element, change observation height
how can background emiision interferences be avoided?
measuring background either side of emission line and subtracting mean
how can the matrix effect caused by changes occurring during nebulisation or sample introductin be avoided?
matrix matching
what is another matrix effect?
Effects in plasma where widely varying amounts of other elements influence the excitation process
3 parameters can be optimised during analysis, what are they?
observation height, RF power level, 3 separate Ar flow rates
What are the 2 factors which govern choice of wavelength?
intensity and freedom for atomic spectral interference
The most intense line normally used, why would less intense lines be used?
may avoid need for dilution with high concentrations or to avoid spectral interferences
what is observation height?
the height of the plasma tail flame at which measurements are made
lower height = ……. temp
higher
What are 5 advantages of ICP?
offers similtaneous analysis capability, high t plasma gives large choice of emission lines for wide range of elements, good detection limit and precision, long linear calibration range
what are 2 disadvantages of ICP?
Costly, innacurate identification
What technique, out of all discussed, is favoured for analysis of gunshot residue elements?
GFAAS
What are 3 forensic applications of ICPAES, GFAAS, and FAAS?
analysis of bullet fragments, metal analysis, antifraud
What techniques are best suited for trace elements in foods? Why?
GFAAS, HGAAS, CVAAS due to excellent sensitivity
