Adventures in
Sample Introduction
for ICP-OES and ICP-MS
Adventures in
Sample Introduction
for ICP-OES and ICP-MS
Geoffrey N. ColemanMeinhard Glass Products
A Division of Analytical Reference Materials International
2
Sample Introduction Components
•ICP Torches
•Spray Chambers
•Nebulizers•Conventional
•High Efficiency
•Direct injection
•Accessories
3
Overview
•Brief review
•Components•Torches
•Spray chambers
•Nebulizers
•What’s new....
4
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).
5
Processes
Starting with a “homogeneous” solution sample....
•Nebulization
•Desolvation
•Dissociation
•ExcitationAll require energy and time.There is a “domino” effect.
6
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.
7
Mean Droplet Size
d3,2
0.5
0.5
0.45 3l
g
1.5585
V597
10 Q
Q +
( )
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.
8
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.
9
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
10
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
11
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.
12
ICP Plasma Torches
•Tg 6000 – 9000 K
•Skin Effect•Electric
•Magnetic
•Pressure/Temperature
•Injection Velocity3 – 5 m/sec to overcome skin effectsInjector 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
13
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
14
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
15
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
16
ICP Spray Chambers
Particle Motion in a Spray Chamber
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ICP Spray Chambers
Scott Double-Pass• Large volume (> 100 mL)
• Large surface area•Phase equilibria
• Stagnant areas
• Long stabilization time
• Long washout
• Drainage
18
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
19
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
20
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
21
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
22
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.
d3,2
0.5
0.5
0.45 3l
g
1.5585
V597
10 Q
Q +
( )
23
Self-Aspirating Nebulizers
•Concentric•Gouy design (1897)
•Efficiency approaching 3%
•Glass
•Quartz
•Teflon
•Cross-flow•Efficiency approaching 2.5%
•Glass
•Sapphire
24
Self-Aspirating Nebulizers
Glass Concentric
25
Self-Aspirating Nebulizers
Glass Concentric
26
Self-Aspirating Nebulizers
27
Self-Aspirating Nebulizers
28
Self-Aspirating Nebulizers
Cross-flow
29
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
30
Non-aspirating Nebulizers
V-groove (Babington)
31
Non-aspirating Nebulizers
• GEM Cone (PerkinElmer)
•Efficiency ~ 1.2%
• MiraMist/Parallel-Path (Burgener)
•Efficiency approaching 3 %
32
Non-aspirating Nebulizers
• MiraMistParallel-Path
33
Non-aspirating Nebulizers
Ultrasonic Nebulizer• Efficiency approaches 30%
• Sensitivity improves ~10x
• Droplet size < 5 m
• Potentially heavy solvent load
• Desolvation essentialMembrane separator available
• Desolvation interferences occur (eg., As III vs. As IV)
• Does not handle high solids well
34
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
35
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
36
Sample Introduction Accessories
•Fit Kits couple liquid and gas supplies to the nebulizer
•Especially useful for high pressure nebulizers
37
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
38
The MEINHARD®
Nebulizer
0
0.2
0.4
0.6
0.8
1
1.2
%R
SD
Cd Cu Fe Mn
Element
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
0
20
40
60
80
100
120
140
160
180
200
PP
B
Cd Cu Fe Mn
Element
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
0
0.5
1
1.5
2
2.5
3
3.5
4
PP
B
Cd Cu Fe Mn
Element
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
0
2000
4000
6000
8000
10000
12000
Co
un
ts
Cd Cu Fe Mn
Element
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
Inte
nsit
y,
40
pp
bP
recis
ion
, 40
pp
bB
EC D
L
39
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
40
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
41
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
42
HF-Resistant Kits
Complete Kits include:
•Demountable Torch
•Pt or Sapphire Injector
•Adapter
•Teflon PFA Spray Chamber
•Teflon PFA or Polypropylene Nebulizer
43
Nebulizers
44
Nebulizers
45
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
d3,2
0.5
0.5
0.45 3l
g
1.5585
V597
10 Q
Q +
( )
46
High Efficiency Nebulizer
Type A HEN
47
High Efficiency Nebulizer
48
High Efficiency Nebulizer
PN: TR-30-A3 MicroConcentric Nebulizer (Cetac) MicroMist (Glass Expansion)
49
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.
50
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
51
High Efficiency Nebulizer
52
High Efficiency Nebulizer
•Type A Nozzle Geometry
•Smaller Sample Uptake Capillary
Liquid flow rate from 10-1200 l/min
•Small Bore Sample InputLow Dead Volume Connection (LC, CZE)
•Smaller Gas Annular AreaHigher Ar pressure - 150 psig
53
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
54
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
55
DIHEN
•Typical demountable torch with DIHEN in place
•Detection limits better than conventional pneumatic nebulizer
•Detection limits not as good as HEN