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

17

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