ICP

Question 1

what does ICP stand for?

Answer 1

inductively coupled plasma

Question 2

An ICP torch is a devicce that produces a plasma - which is a fireball of what?

Answer 2

atoms, ions and electrons interacting at very high energies with temp of up to 10000 K

Question 3

what does exposing a sample to the high temp plasma do?

Answer 3

converts a very large proportion of its constituent atoms to an excited state

Question 4

ICP-AES can identify and determine how many elements? and with what detection limits?

Answer 4

0, ppb

Question 5

if a sample consists of more than metal, there will be multiple emissions - what is requied for this?

Answer 5

suitable polychromators and scanning monochromator to allow multi-element analysis

Question 6

Why is emission spectrum more complex?

Answer 6

because emission can occur to other excited states

Question 7

The fuel and oxidant of flame is replaced by what?

Answer 7

Ar

Question 8

Powerful radio-frequency electrical current is applied to what?

Answer 8

Cu load coil

Question 9

the rf current has an associated magnetic field with lines of force passing along what?

Answer 9

axis of a quartz tube places inside the coil

Question 10

A spark is applied, which ionises what?

Answer 10

a few Ar atoms

Question 11

What happens to the electrons which are formed?

Answer 11

they are rapidly accelerated to and fro in circular orbits by rapidly alternating electric field

Question 12

What do the collisions cause the gas to do?

Answer 12

heat up to a high temp of 10000K forming plasma

Question 13

In the plasma torch, outside flow is used as what?

Answer 13

coolant to prevent tube melting

Question 14

what maintains the plasma in plasma torch?

Answer 14

auxiliary flow

Question 15

What carries the nebulised sample?

Answer 15

central injector

Question 16

a hole is punched through the plasma creating a doughnut shape by what?

Answer 16

injector gas flow

Question 17

why is the nebuliser different in ICP than flame?

Answer 17

lower flow rate of carrier gas employed

Question 18

Name the 3 types of nebuliser?

Answer 18

babington, crossed flow, meinhard

Question 19

What is the difference between crossed bow nebuliser and nebuliser in AAS?

Answer 19

nebuliser in ICP has finer bores

Question 20

what does the high speed Ar flowing past tip of capillary create?

Answer 20

a low pressure region into which solution is aspirated as an aerosol

Question 21

What kind of sample is a babington nebuliser used for?

Answer 21

slurries and viscous liquids

Question 22

The sample flows over spherical surface and is converted into what?

Answer 22

an aerosol as high speed of Ar is forced through tiny hole in surface

Question 23

In Meinhard nebuliser, the sample is transported to tip via what?

Answer 23

Bermouli effect

Question 24

The high velocity gas flowing around tip of tube does what?

Answer 24

breaks up liquid into fine drops then carried to plasma

Question 25

The basic detection system for ICP-AES consists of 3 main components, the first of which are collimating lenses/mirrors. What is their purpose?

Answer 25

Focus emitted light through an entrance slit on to the diffraction grating which disperses the emitted light

Question 26

what are the other components of ICP-AES detector?

Answer 26

means of separating individual wavelengths, photomultiplier tubes

Question 27

what are the 2 main designs for detection commercially available?

Answer 27

similtaneous, sequential

Question 28

What are the 2 simultaneous spectrometers called?

Answer 28

polychromator, spectrograph

Question 29

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?

Answer 29

20

Question 30

What is a stepper motor used for in polychromator?

Answer 30

used to move entrance slit to scan peaks

Question 31

Polychromator can be used for rapid routine analysis, give 2 disadvantages to this technique

Answer 31

more expensive then sequential instruments and not as versatile

Question 32

What kind of spectrometer does a spectrograph utilise?

Answer 32

echelle

Question 33

What is a stepper motor used for in sequential spectrometers?

Answer 33

used to move grating or entrance slit and PMT

Question 34

Sequential spectrometers utilise slew scanning - what is this?

Answer 34

Has two speeds of scan, first fast (slews) to wavelength near line of interest, then slower to scan across line in small steps

Question 35

able to slew .. elements and record .......... in less than .. minutes

Answer 35

15, intensities, 5

Question 36

What are 2 disadvantages to slew scanning?

Answer 36

Generally slow and consume more sample than multichannel instruments

Question 37

sequential Uses scanning ........... and single ..............

Answer 37

monochromator, photomultiplier

Question 38

how is the monochromator scanned in sequential?

Answer 38

using a stepper motor under computer control

Question 39

What does a scanning echelle operate as?

Answer 39

scanning or simultaneous multichannel instrument

Question 40

What does aperture plate consist of in scanning echelle of sequential spectrometers?

Answer 40

consists of lots of slits corresponding to different elements spectral line

Question 41

is scanning echelle able to run in slew scanning mode?

Answer 41

yes

Question 42

How can scanning echelle be made multichannel?

Answer 42

if several PMTs are mounted behind appropriate slits in aperture plate

Question 43

If an analysis was needed to be done on samples of various concentrations/elements rapidly, what spectrometer would you opt for?

Answer 43

similtaneous

Question 44

If the sample type is relatively constant and speed of analysis is important, which system would be preferred?

Answer 44

polychromator

Question 45

In a general lab, the monochromator system is the preferred system - why?

Answer 45

usually designed to scan in important 190-450nm region

Question 46

What are 3 advantages of sequential?

Answer 46

cost, flexibility, and allows optimisation of parameters

Question 47

What are 3 advantages of similtaneous?

Answer 47

speed, accuracy and precision since 1 channel can be set for IS

Question 48

How can the spectral interference of adjacent atomic lines overlapping be avoided? 2

Answer 48

applying correction for other element, change observation height

Question 49

how can background emiision interferences be avoided?

Answer 49

measuring background either side of emission line and subtracting mean

Question 50

how can the matrix effect caused by changes occurring during nebulisation or sample introductin be avoided?

Answer 50

matrix matching

Question 51

what is another matrix effect?

Answer 51

Effects in plasma where widely varying amounts of other elements influence the excitation process

Question 52

3 parameters can be optimised during analysis, what are they?

Answer 52

observation height, RF power level, 3 separate Ar flow rates

Question 53

What are the 2 factors which govern choice of wavelength?

Answer 53

intensity and freedom for atomic spectral interference

Question 54

The most intense line normally used, why would less intense lines be used?

Answer 54

may avoid need for dilution with high concentrations or to avoid spectral interferences

Question 55

what is observation height?

Answer 55

the height of the plasma tail flame at which measurements are made

Question 56

lower height = ....... temp

Answer 56

higher

Question 57

What are 5 advantages of ICP?

Answer 57

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

Question 58

what are 2 disadvantages of ICP?

Answer 58

Costly, innacurate identification

Question 59

What technique, out of all discussed, is favoured for analysis of gunshot residue elements?

Answer 59

GFAAS

Question 60

What are 3 forensic applications of ICPAES, GFAAS, and FAAS?

Answer 60

analysis of bullet fragments, metal analysis, antifraud

Question 61

What techniques are best suited for trace elements in foods? Why?

Answer 61

GFAAS, HGAAS, CVAAS due to excellent sensitivity