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analytical chemistry > ICP > Flashcards

ICP Flashcards

1
Q

what does ICP stand for?

A

inductively coupled plasma

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2
Q

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

A

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

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3
Q

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

A

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

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4
Q

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

A

0, ppb

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5
Q

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

A

suitable polychromators and scanning monochromator to allow multi-element analysis

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6
Q

Why is emission spectrum more complex?

A

because emission can occur to other excited states

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7
Q

The fuel and oxidant of flame is replaced by what?

A

Ar

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8
Q

Powerful radio-frequency electrical current is applied to what?

A

Cu load coil

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9
Q

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

A

axis of a quartz tube places inside the coil

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10
Q

A spark is applied, which ionises what?

A

a few Ar atoms

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11
Q

What happens to the electrons which are formed?

A

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

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12
Q

What do the collisions cause the gas to do?

A

heat up to a high temp of 10000K forming plasma

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13
Q

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

A

coolant to prevent tube melting

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14
Q

what maintains the plasma in plasma torch?

A

auxiliary flow

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15
Q

What carries the nebulised sample?

A

central injector

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16
Q

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

A

injector gas flow

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17
Q

why is the nebuliser different in ICP than flame?

A

lower flow rate of carrier gas employed

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18
Q

Name the 3 types of nebuliser?

A

babington, crossed flow, meinhard

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19
Q

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

A

nebuliser in ICP has finer bores

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20
Q

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

A

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

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21
Q

What kind of sample is a babington nebuliser used for?

A

slurries and viscous liquids

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22
Q

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

A

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

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23
Q

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

A

Bermouli effect

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24
Q

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

A

breaks up liquid into fine drops then carried to plasma

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25
Q

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

A

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

26
Q

what are the other components of ICP-AES detector?

A

means of separating individual wavelengths, photomultiplier tubes

27
Q

what are the 2 main designs for detection commercially available?

A

similtaneous, sequential

28
Q

What are the 2 simultaneous spectrometers called?

A

polychromator, spectrograph

29
Q

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?

A

20

30
Q

What is a stepper motor used for in polychromator?

A

used to move entrance slit to scan peaks

31
Q

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

A

more expensive then sequential instruments and not as versatile

32
Q

What kind of spectrometer does a spectrograph utilise?

A

echelle

33
Q

What is a stepper motor used for in sequential spectrometers?

A

used to move grating or entrance slit and PMT

34
Q

Sequential spectrometers utilise slew scanning - what is this?

A

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

35
Q

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

A

15, intensities, 5

36
Q

What are 2 disadvantages to slew scanning?

A

Generally slow and consume more sample than multichannel instruments

37
Q

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

A

monochromator, photomultiplier

38
Q

how is the monochromator scanned in sequential?

A

using a stepper motor under computer control

39
Q

What does a scanning echelle operate as?

A

scanning or simultaneous multichannel instrument

40
Q

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

A

consists of lots of slits corresponding to different elements spectral line

41
Q

is scanning echelle able to run in slew scanning mode?

A

yes

42
Q

How can scanning echelle be made multichannel?

A

if several PMTs are mounted behind appropriate slits in aperture plate

43
Q

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

A

similtaneous

44
Q

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

A

polychromator

45
Q

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

A

usually designed to scan in important 190-450nm region

46
Q

What are 3 advantages of sequential?

A

cost, flexibility, and allows optimisation of parameters

47
Q

What are 3 advantages of similtaneous?

A

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

48
Q

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

A

applying correction for other element, change observation height

49
Q

how can background emiision interferences be avoided?

A

measuring background either side of emission line and subtracting mean

50
Q

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

A

matrix matching

51
Q

what is another matrix effect?

A

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

52
Q

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

A

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

53
Q

What are the 2 factors which govern choice of wavelength?

A

intensity and freedom for atomic spectral interference

54
Q

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

A

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

55
Q

what is observation height?

A

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

56
Q

lower height = ……. temp

A

higher

57
Q

What are 5 advantages of ICP?

A

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

58
Q

what are 2 disadvantages of ICP?

A

Costly, innacurate identification

59
Q

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

A

GFAAS

60
Q

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

A

analysis of bullet fragments, metal analysis, antifraud

61
Q

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

A

GFAAS, HGAAS, CVAAS due to excellent sensitivity

62
Q
A

analytical chemistry (8 decks)

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