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Analytical > ICP2 > Flashcards

ICP2 Flashcards

1
Q

AES details

A

atoms excited causing photon emission

wavelength characteristic of element

intensity proportional to concentration

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2
Q

Plasma Details

A

hot gaseous cload of atoms, ions and electrons

  • neutral overall
  • no combustion
  • 5000-10000K
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3
Q

Direct Current Plasma Details

A

High voltage between 3 electrodes ionises gas creating plasma

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4
Q

DCP advantages

A

economical

sample tolerance esp liquids

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5
Q

DCP cons

A

Sample doesn’t reach hottest parts (5000K)

unreliable

electrodes consumed

interference from electrodes

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6
Q

Microwave induced plasma details

A

microwave radiation heats gas to plasma

2000K

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7
Q

MIP pros

A

can run on N2

inexpensive

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8
Q

MIP cons

A

low temps

severe matrix effects (from low temps)

easily extinguished

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9
Q

ICP Torch

A

3 concentric tubes encapsulated by RF coil

~8000K

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10
Q

ICP process

A

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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11
Q

ICP pros

A

instantly responsive

very high temps

reproducible

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12
Q

ICP cons

A

consumes a lot of Ar

only 2% of sample reaches plasma

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13
Q

Plasma process

A

solvent vaporisation

melting and Vaporisation of analytes

fragmentation

atomisation

ionisation and excitation

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14
Q

Advantages of Plasma over flame

A
  • 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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15
Q

ICP AES spectrometers pros cons

A

Sequential e.g. photonmultiplier tube

  • more sensitive
  • better signal to noise
  • slower

Simultaneous e.g. CCD

  • fast
  • higher noise
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16
Q

AES spectrometer orientation

A

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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17
Q

AES Interferences

A
  1. Easily ionisable
  2. Background
  3. Dominant Matrix
  4. Wavelength coincidence
  5. Chemical
18
Q

Correcting AES interferences

A

higher temperatures

matrix matching

standard addition

standards

remove interferring

preconcentrate

observe different wavelength

19
Q

ICP MS parts

A
  1. sample introduction
  2. ICP torch
  3. MS interface
  4. Mass separator
  5. detector
20
Q

MS process

A

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

21
Q

Mass Spectrometers

A

Quadrupole

Magnetic sector

double focussing MS

22
Q

Quadrupole details

A

4 rods of alternating polarity

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

23
Q

Quadrupole pros and cons

A

fast simple cheap

only unit resolution

24
Q

Magnetic Sector Details

A

ion beam is curved by magnet

extent ions curve determined by m/z

select m/z by altering magnetic field and accelerating voltage

25
Q

Magnetic Sector pros and cons

A

Higher resolution

limited by energy distribution of ions

expensive

26
Q

Double Focussing MS details

A

electrostatic analyser focusses ion energies allowing for higher resolution

27
Q

Double focussing MS pros and cons

A

highest resolution

less interferences

most expensive

28
Q

MS detectors

A

Electron multiplier

electron channel multiplier

29
Q

MS spectro interferences

A
  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+
30
Q

MS spectro interference solutions

A

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

31
Q

MS Matrix interferences

A

Easily ionisable

High Conc - greater variation, non-reproducible, memory effects

Carbon deposition - blocked cones reduce sensitivity

32
Q

MS Matrix interferences solutions

A

Dilution

Matrix matching

standard addition

internal standard

chemically remove

isotope dilution

33
Q

Collision Cell details

A

polyatomics are larger thus collide more, lose more energy.

energy barrier then removes simply

34
Q

Reaction Cell

A

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+

35
Q

Triple Quad

A

Quad MS

mass shift reaction cell

Quad MS

36
Q

Benefits of MS and con

A

Multielemental

isotope analysis

mos elements interference free

fast

low detection limits

large linear calibration range

only 2% of sample reaches plasma

37
Q

Liquid sample intro

A
  1. Nebulise - creates fine mist to prevent extinguishing

pneumatic or ultrasonic (better)

  1. spray chamber - removes large droplets makes homogeneous
38
Q

Gas Intro and pros

A

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

39
Q

Solid Intro

A

Electrothermal Vaporisation e.g polymers

Laser ablation e.g. rocks - targetted

40
Q

ICP quantification

A

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

41
Q

Electrothermal Vaporisation pros and cons and analytes

A

polymers

pro

good detection limit

con

homogeneous sample

conducting sample

decompose sample

42
Q

Laser Ablation Details, analytes, pros and cons

A

higher energy sputters surface molecules into vapor

rocks or anything

pros

targetted

non conducting

different scan modes

cons

can decompose sample

Analytical (7 decks)

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