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Adventures in Sample Introduction for ICP-OES and ICP-MS. Geoffrey N. Coleman Meinhard Glass Products A Division of Analytical Reference Materials International. Sample Introduction Components. ICP Torches Spray Chambers Nebulizers Conventional High Efficiency Direct injection

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adventures in sample introduction for icp oes and icp ms

Adventures in Sample Introduction for ICP-OES and ICP-MS

Geoffrey N. Coleman

Meinhard Glass Products

A Division of Analytical Reference Materials International

sample introduction components
Sample Introduction Components
  • ICP Torches
  • Spray Chambers
  • Nebulizers
    • Conventional
    • High Efficiency
    • Direct injection
  • Accessories
overview
Overview
  • Brief review
  • Components
    • Torches
    • Spray chambers
    • Nebulizers
    • What’s new....
references
References

Richard F. Browner, Georgia Institute of Technology

Anders G.T. Gustavsson, Swedish Institute of Technology

Jean-Michel Mermet, Universite Claude Bernard-Lyon, France

Akbar Montaser, George Washington University

John W. Olesik, Ohio State University

Barry L. Sharp, Macauley Land Use Institute, Scotland

“Pneumatic Nebulizers and Spray Chambers for Inductively Coupled Plasma Spectroscopy”, Journal of Analytical Atomic Spectrometry, 1988, 3, 613 – 652 (Part 1); 939 – 963 (Part 2).

processes
Processes

Starting with a “homogeneous” solution sample....

  • Nebulization
  • Desolvation
  • Dissociation
  • Excitation

All require energy and time.

There is a “domino” effect.

interferences
Interferences
  • Nebulization
  • Desolvation
  • Dissociation
  • Excitation

Probably 85% of significant interferences occur at nebulization, due to changes in surface tension, density, and viscosity.

These are multiplicative interferences.

mean droplet size

1.5

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Mean Droplet Size

NUKIYAMA AND TANASAWA EQUATION

d3,2 = Sauter mean diameter - (m)

V = Velocity difference of gas-liquid - (m/s)

 = Surface tension - (dyn/cm)

 = Liquid density - (g/cm3)

 = Liquid viscosity - (Poise or dyn·s/cm2)

Ql = Volume flowrate, liquid - (cm3/s)

Qg = Volume flowrate, gas - (cm3/s)

S. Nukiyama and Y. Tanasawa, Trans. Soc. Mech. Eng., Tokyo, 1938-40, Vol. 4 – 6, Reports 1 – 6.

rule of thumb
Rule-of-Thumb

When the Total Dissolved Solids exceeds about 1000 ppm, changes in surface tension, density, and viscosity begin to affect the droplet size distribution and, thus, the slope of the analytical calibration curve.

interferences9
Interferences

Control by:

  • Matrix Removal – usually not practical
  • Swamping – risk of contamination
  • Matrix Matching – probably most useful
  • Internal Standard – line selection
  • Method of Standard Additions – most tedious and time-consuming
single droplet studies
Single Droplet Studies

Desolvation begins

Evaporation from surface

Droplet diameter diminishes

Crust forms as solvent evaporates

Internal pressure builds

Droplet explodes

Escaping water vapor cools immediate surroundings

Particles dehydrate

Particles evaporate

implications
Implications
  • Large Surface Area/Volume
  • Small Droplets
    • Faster desolvation and vaporization
  • Narrow Size Distribution
    • Consistent desolvation and vaporization
    • Well-defined excitation/observation zones
  • Virtually no signal comes from droplets larger than 8 - 10 m
  • Most signal comes from < 3 m.
icp plasma torches
ICP Plasma Torches
  • Tg 6000 – 9000 K
  • Skin Effect
    • Electric
    • Magnetic
    • Pressure/Temperature
  • Injection Velocity

3 – 5 m/sec to overcome skin effects

Injector diameter 1.0 – 2.4 mm i.d.

Carrier at 0.7 – 1.0 L/min

  • Residence Time
  • Highly Volatile Solvents
  • Chemical Interferences
  • Viewing Zone
icp plasma torches13
ICP Plasma Torches

End-on Viewing

  • Must remove “tail flame”
    • Ground state atoms
    • Molecular species
  • Larger injector diameters – longer residence time
  • Significant chemical interferences
  • Significant sensitivity improvement – up to 10x
icp plasma torches14
ICP Plasma Torches
  • Outside: 16 – 18 mm
  • Inner – Outer Gap: 0.5 – 1.0 mm
  • Injector: 1.0 – 4.0 mm
    • 1.0 mm for volatile solvents
    • 2.0 mm general purpose radial torch
    • 2.4 mm general purpose axial torch
  • Demountable Injectors
    • Ceramic (alumina) or sapphire for HF
    • Flexibility
    • Complexity
    • Cost
icp spray chambers
ICP Spray Chambers

Aerosol Conditioning

  • Remove droplets larger than 20 um
    • Gravitational settling
    • Inertial impaction
    • Evaporation
    • Recombination
  • Reduce aerosol concentration
  • Modify aerosol phase equilibria
  • Modify aerosol charge equilibria
  • Reduce turbulence of nebulization
icp spray chambers16
ICP Spray Chambers

Particle Motion in a Spray Chamber

icp spray chambers17
ICP Spray Chambers

Scott Double-Pass

  • Large volume (> 100 mL)
  • Large surface area
    • Phase equilibria
  • Stagnant areas
  • Long stabilization time
  • Long washout
  • Drainage
icp spray chambers18
ICP Spray Chambers

Cyclonic with Baffle

  • Moderate volume: 50 mL
  • Moderate surface area
  • Entire volume swept by carrier flow
  • Fast equilibration
  • Fast washout
  • Sensitivity enhanced by 1.2 – 1.5x
  • Now most common type
icp spray chambers19
ICP Spray Chambers
  • Desolvation begins in the spray chamber
    • Extent affects droplet size
    • Affects amount transported to the plasma
    • Maintain constant temperature
  • Liquid on the walls must equilibrate with vapor
    • Minimize surface area
    • Drain away excess quickly
icp spray chambers20
ICP Spray Chambers
  • Speciation begins in the spray chamber
    • Volatile species in gas phase are more efficiently transported than droplets
    • Nebulization does not control the rate of sample introduction
    • Cool spray chamber (especially for organic solvents)
    • Minimize surface area
nebulizers
Pneumatic

Self-aspirating

Concentric

Cross-flow

Non-aspirating

Babington

V-groove

GEM Cone

MiraMist

Grid

Fritted

Other

Ultrasonic nebulizer

Thermospray

Spark ablation

Laser ablation

Specialty

HEN, MCN, MicroMist

DIHEN, DIN

Nebulizers
mean droplet size22

1.5

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0.5

3

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3,2

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r

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0.5

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Mean Droplet Size

NUKIYAMA AND TANASAWA EQUATION

d3,2 = Sauter mean diameter - (m)

V = Velocity difference of gas-liquid - (m/s)

 = Surface tension - (dyn/cm)

 = Liquid density - (g/cm3)

 = Liquid viscosity - (Poise or dyn·s/cm2)

Ql = Volume flowrate, liquid - (cm3/s)

Qg = Volume flowrate, gas - (cm3/s)

S. Nukiyama and Y. Tanasawa, Trans. Soc. Mech. Eng., Tokyo, 1938-40, Vol. 4 – 6, Reports 1 – 6.

self aspirating nebulizers
Self-Aspirating Nebulizers
  • Concentric
    • Gouy design (1897)
    • Efficiency approaching 3%
    • Glass
    • Quartz
    • Teflon
  • Cross-flow
    • Efficiency approaching 2.5%
    • Glass
    • Sapphire
non aspirating nebulizers
Non-aspirating Nebulizers
  • Original Babington Design (1973)
    • Very inefficient
    • Could nebulize “anything”
  • V-groove (Suddendorf, 1978)
    • Much improved efficiency, > 1%
    • Best choice for analysis of slurries
    • Best choice for analysis of used oils
  • Grid (Hildebrand, 1986)
    • Efficiency approaching 4.5%
    • Very difficult to maintain
non aspirating nebulizers30
Non-aspirating Nebulizers

V-groove

(Babington)

non aspirating nebulizers31
Non-aspirating Nebulizers
  • GEM Cone (PerkinElmer)
    • Efficiency ~ 1.2%
  • MiraMist/Parallel-Path (Burgener)
    • Efficiency approaching 3 %
non aspirating nebulizers32
Non-aspirating Nebulizers
  • MiraMist

Parallel-Path

non aspirating nebulizers33
Non-aspirating Nebulizers

Ultrasonic Nebulizer

  • Efficiency approaches 30%
  • Sensitivity improves ~10x
  • Droplet size < 5 m
  • Potentially heavy solvent load
  • Desolvation essential

Membrane separator available

  • Desolvation interferences occur (eg., As III vs. As IV)
  • Does not handle high solids well
sample introduction accessories
Sample Introduction Accessories

Desolvation: Apex Q from Elemental Scientific

  • Sensitivity improves ~10x
  • Uses concentric nebulizer and cyclonic spray chamber
  • Desolvation interferences
  • High solids problematic
  • Available in HF-resistant version
sample introduction accessories35
Sample Introduction Accessories

Spray Chamber Cooling: PC3 from Elemental Scientific

  • Sensitivity improves
  • Reduces solvent loading
  • Reduces oxide interferences in ICPMS
  • Uses concentric nebulizer and cyclonic spray chamber
  • Available in HF-resistant version
sample introduction accessories36
Sample Introduction Accessories
  • Fit Kits couple liquid and gas supplies to the nebulizer
  • Especially useful for high pressure nebulizers
the meinhard nebulizer
The MEINHARD®Nebulizer

Type A

  • Lapped ends – capillary and nozzle flush
  • Simple, monolithic design

Type C

  • Recessed capillary for higher TDS tolerance
  • Vitreous, fire-polished ends
  • Stronger suction

Type K

  • Recessed capillary
  • Lapped ends
  • Lower Ar flow: 0.7 L/min
the meinhard nebulizer38
The MEINHARD®Nebulizer

Intensity, 40 ppb

Precision, 40 ppb

BEC

DL

the meinhard nebulizer39
The MEINHARD®Nebulizer

Type A

  • Lapped ends – capillary and nozzle flush
  • Simple, monolithic design

Type C

  • Recessed capillary for higher TDS tolerance
  • Vitreous, fire-polished ends
  • Stronger suction

Type K

  • Recessed capillary
  • Lapped ends
  • Lower Ar flow: 0.7 L/min
glass concentric nebulizer
Glass Concentric Nebulizer
  • Advantages
    • Simple, single piece desgin
    • All glass design, inert
    • Permanently aligned - self aligning
    • Easy to use
  • Disadvantages
    • Low efficiency ( ~3%)
    • Glass attacked by HF
    • High or undissolved solids may clog capillary
hf resistant nebulizers
HF-Resistant Nebulizers
  • Concentric nebulizers in Teflon PFA and Polypropylene from Elemental Scientific
  • Typical flows: 50 – 700 L/min; 1 L/min
  • Integral or demountable solution tubing
  • Efficiency: 2 – 3%

MicroFLOW PFA

PolyPro

hf resistant kits
HF-Resistant Kits

Complete Kits include:

  • Demountable Torch
  • Pt or Sapphire Injector
  • Adapter
  • Teflon PFA Spray Chamber
  • Teflon PFA or Polypropylene Nebulizer
mean droplet size45

1.5

0.45

0.5

3

ù

h

é

ù

é

10

Q

é

ù

585

s

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597

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ê

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ê

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ê

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3,2

ë

û

V

r

Q

0.5

ë

û

(

sr

)

ë

û

g

Mean Droplet Size

NUKIYAMA AND TANASAWA EQUATION

d3,2 = Sauter mean diameter - (m)

V = Velocity difference of gas-liquid - (m/s)

Ql = Volume flowrate, liquid - (cm3/s)

Qg = Volume flowrate, gas - (cm3/s)

  • Adjust annulus to increase V, but maintain Qg
  • Adjust capillary to decrease Ql
high efficiency nebulizer48
High Efficiency Nebulizer

PN: TR-30-A3 MicroConcentric Nebulizer (Cetac) MicroMist (Glass Expansion)

high efficiency nebulizer49
High Efficiency Nebulizer
  • The HEN normally aspirates 30 – 300 L/min
  • Design gas flow is 1 L/min of argon
  • Normal operating pressure is 170 psi, 150 and 90 psi versions are available.
high efficiency nebulizer50
High Efficiency Nebulizer
  • Under normal operating conditions, a HEN exhibits a D3,2 of 1.2 – 1.5 m
  • “Starved” TR-30-A3 exhibits D3,2 of 3.2 – 4.2 m
  • Normal operating conditions for a TR-30-A3 yield a mean droplet size of about 15 m
high efficiency nebulizer52
High Efficiency Nebulizer
  • Type A Nozzle Geometry
  • Smaller Sample Uptake Capillary
      • Liquid flow rate from 10-1200 ml/min
  • Small Bore Sample Input
      • Low Dead Volume Connection (LC, CZE)
  • Smaller Gas Annular Area
      • Higher Ar pressure - ³150 psig
high efficiency nebulizer53
High Efficiency Nebulizer

Applications:

  • Chromatography detection
    • Capillary electrophoresis
    • Liquid chromatography
  • Limited sample volume
  • Minimize speciation interferences
    • Very high analyte transport
    • Much less discrimination between volatile species and dissolved species
direct injection hen
Direct Injection HEN
  • DIHEN is designed to be inserted directly into a demountable torch
  • DIHEN is dimensionally similar to HEN (see table, slide 47)
  • DIHEN is operationally similar to HEN, except
    • Normal carrier flow is 0.2 – 0.4 L/min
  • Minimize speciation interferences
  • Easily introduce highly volatile solvents
  • Essentially 100% transport
  • Large-Bore version less prone to clogging, but noisy
dihen
DIHEN
  • Typical demountable torch with DIHEN in place
  • Detection limits better than conventional pneumatic nebulizer
  • Detection limits not as good as HEN