Transcript 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
•ICP Torches
•Spray Chambers
•Nebulizers
•Conventional
•High Efficiency
•Direct injection
•Accessories
2
Overview
•Brief review
•Components
•Torches
•Spray chambers
•Nebulizers
•What’s new....
3
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).
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Processes
Starting with a “homogeneous” solution
sample....
•Nebulization
•Desolvation
•Dissociation
•Excitation
All require energy and time.
There is a “domino” effect.
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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.
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Mean Droplet Size
NUKIYAMA AND TANASAWA EQUATION
585  s 
d
3,2 = V  r 
0.5
 h

+ 597 
 (sr ) 0.5 
0.45
 10 3 Q 
l
 Q

g
1.5
d3,2 = Sauter mean diameter - (m)
V = Velocity difference of gas-liquid - (m/s)
s = Surface tension - (dyn/cm)
r = Liquid density - (g/cm3)
h = 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.
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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.
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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
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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
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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.
•
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Mean Droplet Size
NUKIYAMA AND TANASAWA EQUATION
585  s 
d
3,2 = V  r 
0.5
 h

+ 597 
 (sr ) 0.5 
0.45
 10 3 Q 
l
 Q

g
1.5
d3,2 = Sauter mean diameter - (m)
V = Velocity difference of gas-liquid - (m/s)
s = Surface tension - (dyn/cm)
r = Liquid density - (g/cm3)
h = 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.
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Self-Aspirating Nebulizers
•Concentric
•Gouy design (1897)
•Efficiency approaching 3%
•Glass
•Quartz
•Teflon
•Cross-flow
•Efficiency approaching 2.5%
•Glass
•Sapphire
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Self-Aspirating Nebulizers
Glass Concentric
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Self-Aspirating Nebulizers
Glass Concentric
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Self-Aspirating Nebulizers
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Self-Aspirating Nebulizers
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Self-Aspirating Nebulizers
Cross-flow
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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
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Non-aspirating
Nebulizers
V-groove
(Babington)
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Non-aspirating
Nebulizers
• GEM Cone (PerkinElmer)
•Efficiency ~ 1.2%
• MiraMist/Parallel-Path
(Burgener)
•Efficiency approaching 3 %
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Non-aspirating
Nebulizers
• MiraMist
Parallel-Path
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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
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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
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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
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Sample Introduction
Accessories
•Fit Kits couple liquid
and gas supplies to the
nebulizer
•Especially useful for
high pressure
nebulizers
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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
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12000
1
0.8
8000
%RSD
Counts
10000
6000
0.2
2000
0
Cd
Cu
Fe
Mn
Cd
Cu
Mn
4
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
180
160
140
TR-30-A3(8)
3.5
TR-30-A3(1)
TR-30-C1(12)
3
TR-30-K2/3(22)
2.5
PPB
120
100
80
DL
PPB
Fe
Element
Element
200
BEC
0.6
0.4
4000
0
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
1.2
TR-30-A3(8)
TR-30-A3(1)
TR-30-C1(12)
TR-30-K2/3(22)
Precision, 40 ppb
Intensity, 40 ppb
The MEINHARD®
Nebulizer
2
1.5
60
1
40
0.5
20
0
Cd
Cu
Fe
Element
Mn
0
Cd
Cu
Fe
Mn
Element
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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
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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
40
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
41
HF-Resistant Kits
Complete Kits include:
•Demountable Torch
•Pt or Sapphire Injector
•Adapter
•Teflon PFA Spray
Chamber
•Teflon PFA or
Polypropylene
Nebulizer
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Nebulizers
43
Nebulizers
44
Mean Droplet Size
NUKIYAMA AND TANASAWA EQUATION
585  s 
d
3,2 = V  r 
0.5
 h

+ 597 
 (sr ) 0.5 
0.45
 10 3 Q 
l
 Q

g
1.5
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
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High Efficiency Nebulizer
Type A
HEN
46
High Efficiency Nebulizer
47
High Efficiency Nebulizer
PN: TR-30-A3
MicroConcentric Nebulizer (Cetac) MicroMist (Glass Expansion)
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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.
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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 TR30-A3 yield a mean
droplet size of about
15 m
•
•
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High Efficiency Nebulizer
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High Efficiency Nebulizer
•Type A Nozzle Geometry
•Smaller Sample Uptake Capillary
Liquid flow rate from 10-1200 l/min
•Small Bore Sample Input
Low Dead Volume Connection (LC, CZE)
•Smaller Gas Annular Area
Higher Ar pressure - 150 psig
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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
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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
54
DIHEN
•Typical demountable torch with DIHEN in place
•Detection limits better than conventional pneumatic
nebulizer
•Detection limits not as good as HEN
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