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

Overview Brief review Components Torches Spray chambers Nebulizers What’s new....

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 Nebulization Desolvation Dissociation Excitation Starting with a “homogeneous” solution sample.... Nebulization Desolvation Dissociation Excitation All require energy and time. There is a “domino” effect.

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.

NUKIYAMA AND TANASAWA EQUATION Mean Droplet Size NUKIYAMA AND TANASAWA EQUATION d 3,2 0.5 0.45 3 l g 1.5 585 V 597 10 Q + = é ë ê ù û ú s r h sr ( ) 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 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.

Interferences Matrix Removal – usually not practical 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 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 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 Tg 6000 – 9000 K Skin Effect Injection Velocity 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 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 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 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

Particle Motion in a Spray Chamber ICP Spray Chambers Particle Motion in a Spray Chamber

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 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 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 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 Other Specialty Self-aspirating Non-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

NUKIYAMA AND TANASAWA EQUATION Mean Droplet Size NUKIYAMA AND TANASAWA EQUATION d 3,2 0.5 0.45 3 l g 1.5 585 V 597 10 Q + = é ë ê ù û ú s r h sr ( ) 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 Concentric Gouy design (1897) Efficiency approaching 3% Glass Quartz Teflon Cross-flow Efficiency approaching 2.5% Sapphire

Self-Aspirating Nebulizers Glass Concentric

Self-Aspirating Nebulizers Glass Concentric

Self-Aspirating Nebulizers

Self-Aspirating Nebulizers

Self-Aspirating Nebulizers Cross-flow

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 Nebulizers V-groove (Babington)

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

Non-aspirating Nebulizers MiraMist Parallel-Path

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 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 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 Accessories Fit Kits couple liquid and gas supplies to the nebulizer Especially useful for high pressure nebulizers

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® Nebulizer Intensity, 40 ppb Precision, 40 ppb BEC DL

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 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 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 Complete Kits include: Demountable Torch Pt or Sapphire Injector Adapter Teflon PFA Spray Chamber Teflon PFA or Polypropylene Nebulizer

Nebulizers

Nebulizers

NUKIYAMA AND TANASAWA EQUATION Mean Droplet Size NUKIYAMA AND TANASAWA EQUATION d 3,2 0.5 0.45 3 l g 1.5 585 V 597 10 Q + = é ë ê ù û ú s r h sr ( ) 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 Nebulizer Type A HEN

High Efficiency Nebulizer

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

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 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 Nebulizer

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 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 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 Typical demountable torch with DIHEN in place Detection limits better than conventional pneumatic nebulizer Detection limits not as good as HEN