Transcript Characterization of Tertiary Aerosols in ICP-AES

Characterization of Tertiary
Aerosols in ICP-AES
Jerry Dulude and Bobby Brezni
Glass Expansion
Melbourne, Australia
Salar Samii, Jonathan A. Levine, Kaveh Kahen, and Akbar Montaser
The George Washington University
Department of Chemistry
Washington, DC 20052
Overview
• Purpose: to characterize primary &
tertiary aerosols related to ICP-AES &
ICP-MS
• Methods: gravimetric and optical
measurements
• Results: Droplet size & transport
efficiency are related to gas flow,
nebulizer and spray chamber design,
and transport efficiency.
Introduction
The nature of the aerosol mist typically
generated by the combination of a
nebulizer and spray chamber has a
pronounced effect on the performance
of the ICP atomic emission spectrometer
into which it is directed. This work
reports on the relationships between the
efficiency of the sample introduction
system and the mean droplet size
including the effect of nebulizer gas
velocity and salt content.
Definitions
• Primary Aerosol:
the aerosol that
exits from the
nebulizer (A)
• Tertiary Aerosol:
the aerosol that
exits from the spray
chamber (B)
• Waste (W) =A-B
• Transport Eff.: % of
nebulized sample
leaving the
chamber
B
A
W
Experimental:
Transport Efficiency
For each nebulizer/spray chamber combination:
1. Aspirate solution for an appropriate time
period using self-aspiration.
2. Measure by weight the mass of solution
consumed.
3. Measure by weight the mass of solution
collected at the drain.
4. The difference between 2 and 3 is the
transport efficiency.
Measurement of Droplet Size
Distributions
•
•
•
•
The Phase Doppler Particle Analyzer was used
Simultaneous measurement of size & velocity
Size range = 0.5 to 680 mm
Velocity range = -585 to +585 m/sec
The Phase Doppler Particle Analyzer
Transmitting
probe
Ar+ laser
Fiberoptics
light coupler
Measurement
volume
Receiver
optics
Computer
Measurement
electronics
PMT
detectors
Transport Efficiency Study
7 different nebulizers run at 1.0LPM gas flow and their
natural uptake rate.
Uptake rate
Nebulizer P/N
(ml/min)
AR30-1-FC2E
AR30-1-FC1E
AR30-1-FM06E
AR30-1-FM04E
AR30-1-FM02E
AR30-1-FM01E
AR30-1-FM005E
2.1
1.4
0.61
0.50
0.27
0.11
0.03
Transport Efficiency vs. Uptake
60
%EFFICIENCY
50
40
30
Efficien
20
10
0
0.03
0.11
0.27
0.5
0.61
1.4
UPTAKE RATE (ML/MIN)
2.1
Tertiary Flow Rate vs. Uptake
Tertiary Flow Rate
(ul/min)
50
45
40
35
30
25
20
15
10
5
0
ul/min
0.03
0.11
0.27
0.5
0.61
1.4
UPTAKE RATE (ML/MIN)
2.1
Corroboration of Tertiary Flow Rates
Uptake rate
(ml/min)
This work
(mg/min)
Todoli paper*
(mg/min)
0.03
15
14
0.11
23
21
•Todoli, Hernandis, Canals, and Mermet, JAAS, 1999, 14, 1289-1295
Using GE MicroMist nebulizer with U-tube absorption for measurement
Inter-nebulizer Variability of
Transport Efficiency (AR30-07-FC2E)
3
2.5
2
1.5
Conikal
1
0.5
0
1
2
3
4
DIFFERENT NEBULIZERS OF SAME MODEL
3.6%RSD
Effect of Gas Flow Rate
48% Increase in Efficiency
4
3.5
3
2.5
2
Tertiary Eff.
1.5
1
0.5
0
0.7LPM
1.0LPM
NEBULIZER GAS FLOW RATE (LPM)
AR30-07-FC2E
AR30-1-FC2E
43% increase in analyte dilution in the plasma
Effect of Gas Pressure
4
3.5
3
2.5
2
Tert. Eff.
1.5
1
0.5
0
30
40
50
NEBULIZER GAS PRESSURE (PSIG)
Effect of Spray Chamber Design
4
3.69
3.39
3.5
2.91
3
2.5
2
Tert. Eff.
1.5
79%
92%
1
0.5
0
Cyclonic
Baffled Cyc
Mini-Cyc
Spray Chamber Designs
Cyclonic
Tracey™
Baffled Cyclonic
Twister™
Mini-Cyclonic
Cinnabar™
Effect of Chamber Volume
120
100
80
Rel.
60
Speed
velocity
cyclonic
40
20
0
0
5 10 15 20 25 30 35 40 45
Distance from Neb (mm)
Mini-cyclonic
Effect of Dissolved Salts
Conikal™ at 2ml/min uptake
4
3.69
3.5
3.27
3.4
3
2.5
2
Tert. Eff.
89%
1.5
92%
1
0.5
0
0
DIW
1% NaCl
1% CaCl
Primary Aerosol Size Distribution
Nebulizer Gas Flow Rate = 1.0 L/Min Solution Uptake Rate = Natural Aspiration
Conikal (FC2E)
1001
0.8
60
0.6
0.4
20
0.2
0
D32 = 17.2
0
10
20
30
40
50
60
Diameter (microns)
MicroMist (FM005E)
100
Normalized Volume
Normalized Count
Conikal Primary
D32 = 7.1
60
20
0
10
20
30
40
Diameter (mm)
50
Normalized VolumeNormalized Volume
Normalized Count
Conikal Primary
60
1
0.8
0.6
0.4
0.2
0
0
10
20
30
40
50
60
Diameter (microns)
MicroMist Primary
1
0.8
0.6
0.4
0.2
0
0
10
0
10
20
30
40
50
60
20 Diameter
30(microns)40
50
60
Diameter (mm)
Tertiary Aerosol Size Distribution
Nebulizer Gas Flow Rate = 1.0 L/Min Solution Uptake Rate = Natural Aspiration
Baffled Cyclonic Spray Chamber
Conikal Tertiary
Conikal
Normalized Count
D32 = 4.9
0.8
0.6
60
0.4
20
0.2
0
0
10
20
30
40
50
MicroMist
Tertiary
Diameter
(microns)
MicroMist
1001
Normalized Count
Normalized Count
1001
D32 = 5.0
0.8
0.6
60
0.4
0.2
20
0
0
10
0
10
20
30
Diameter
(microns)
20
30
Diameter (mm)
40
40
50
50
Conclusions
• Uptake of 0.6 ml/min gives max tertiary
transport
• Baffled spray chamber lowers cutoff
droplet size
• Salts lower transport efficiency
• Low uptake produces smaller primary
D32
• No effect on tertiary D32