Sample Introduction System –Liquid

• Peristaltic pump or automated sampling system

• Nebulizer

• Spray chamber

• Plasma torch

Sample Introduction System

• Peristaltic Pump

– Pump liquid sample towards nebulizer and plasma torch

Sample Introduction System

• NEBULIZER

– Its function is to mix the liquid sample with the nebulizer gas (Argron) to produce a fine sample aerosol for introduction to the plasma discharge area.

Sample Introduction System

• NEBULIZERS– 3 main categories

• Pneumatic - concentric, cross flow, Babington, v-groove, ConeSpray

• Ultrasonic

• Direct insertion

Liquid sample – aspiratedeither in ‘free aspiration’mode or with a peristalticpump

Ar gas (0.6 to 1.2 L/min)

Aerosol production

-usually made of glass or variouskinds of polymers (for highly corrosiveliquids/samples)

Concentric nebulizers

Concentric nebulizers

• “Self-actuating”– Solutions are drawn up by the pressure drop

generated as the nebulizer gas passes through the orifice – also referred to as “free-running” or “self-aspiration”. Thus, a peristaltic pump is not necessarily required.

• Advantage-– Generally, the ion signal is much more stable

Concentric nebulizers

• Disadvantages– cannot handle high total dissolved salts (TDS

- 0.25% m/v solids); i.e. 250 mg sample dissolved in 100 g of solution

– samples with different viscosities will have different flow rates

– liquid uptake tied to nebulizer gas flow– cannot easily increase flow for different

samples

Optimal Ar gas flow rate

Concentric nebulizers• However……..• Can use concentric nebulizer in conjunction with

peristaltic pump - more commonly used than self-aspirating mode

• viscosity effects are reduced

• liquid uptake is metered by pump rate

• pump rate can be changed for each sample

• Disadvantages- Can occasionally lead to poorer precision due to

“pulsing” of the flow

Ion signal ‘pulsing’

Cross-flow nebulizers• Ar flow move across the tip of a capillary that

carries solution

• pressure reduction draws liquid up the capillary

• more resistant to clogging than Meinhard

• used with peristaltic pump

• similar in performance to Meinhard nebs

-optimal for samples that containa heavy matrix or small amountsof undissolved matter

Babington nebulizers• solution allowed to flow over a sphere

• gas pumped through an aperature which nebulizes the solution (liquid film)

• very resistant to high TDS (can nebulizeslurries!) – solutions are not flowing through tubing with small internal diameters

• very bad memory effects

• must be pumped

Babington Nebulizer

V-groove nebulizers – high TDS neb

• variant of the Babington

• solution pumped through orifice and allowed to flow down a v-shaped groove

• gas flows through another orifice which nebulizes the solution

• very resistant to high TDS

High-TDS nebs• Advantages:

– Capacity to analyze high TDS samples

– many are constructed of corrosion-resistant materials (i.e., PFTE)

– can aspirate HF or NaOH

• Disadvantages

– memory effects are usually severe

– even less efficient than concentric/crossflow

Hildebrand nebulizer (high TDS)

Pneumatic Nebulizers

• The problem with concentric and cross-flow nebulizers is that they produce only approx. 1% of droplets of the correct size to attain the plasma!

Ultrasonic Nebulizers (USN)• Sample solution is fed to the surface of a peizoelectric

transducer operated at a frequency of between 0.2 and 10 MHz.

• The longitudinal wave, propagated at right angles to the surface of the transducer towards the liquid-air interface, produces pressure that breaks the surface into an aerosol.

• Production of aerosols is very efficient and independent of gas flow rate (unlike pneumatic nebulizers).

Ultrasonic nebulizers

• Advantages:

– high efficiency - typically order of magnitude greater sensitivity compared to pneumatic nebulizers

– better detection limits

Ultrasonic nebulisers• Disadvantages:

– Long wash-out times

– LOTS of glassware that the aerosol passes through

– No HF or NaOH matrices

– Bad memory effects

– Cost

Aridus desolvating nebulizer

• ideal for low-volume applications (uptake of 60 uL/min; < 1 mL total volume)

• desolvating via heated PFTE membrane built of inert components

• shorter washout times compared to USN while retaining many of the benefits

• However, ………

Spray Chamber• Its function is to eliminate all droplets with the

exception of those that are the correct size and velocity for introduction into the plasma since plasma discharge is inefficient at dissociating large droplets (>10 micron- 1x10-6 metres). The latter are eliminated by gravity and exit through a drain tube.

• An aerosol with a diameter of ~1-5 microns is considered to have an ideal diameter for introduction into the plasma.

• Its secondary purpose is to smooth out pulses that occur during the nebulization process

Example of wet plasma introduction system

-Spray chamber is cooledto 5°C in order to providethermal stability, minimizethe amount of sample enteringthe plasma, and reducing the quantity of oxide species.

-Oxide species (M+O- vs. M+) should be kept to below 3% of total ion signal;If not, then the plasma has not beencorrectly fine-tuned.

Desolvating Introduction System- ‘Dry’Plasma (e.g. DSN-100, Nu Instruments)

DSN-100

• The main purpose of the heated spray chamber and PTFE membrane is to drive-off water from the sample, and thus reducing the overall size of the aerosols (hence the term ‘dry’ plasma).

• This action results in increasing the instrument’s ‘sensitivity’; i.e. the DSN-100 introduction system yields ~10 times more ion signalcompared to a meinhard nebulizer + cyclonic spray chamber (wet plasma) introduction system.

DSN-100

• Sample aspiration occurs in ‘free aspiration’mode, typically at a rate of 50 to 100 microlitresper minute, with a Meinhard (micromist) nebulizer

• The ‘nebulized’ sample (fine aerosols) are introduced into a heated (110ºC) spray chamber, where it is vapourized

• The vapourized sample is then carried into a heated (110ºC), semi-porous PTFE membrane wall and then transported away by an external gas stream (membrane gas flow)

Torches

• 2 main types: fixed and demountable

• fixed: 1 piece

• demountable: injector tube removable

Torches

• typically constructed of quartz glass

• injector tubes can be made of a variety of materials

• alumina tubes for HF solutions

• injector tubes can have varying diameters to accept a range of TDS solutions

Sample Introduction Systems - Liquid

HPLC – High Performance Liquid Chromatography

Hydride Generation

High-performance liquid chromatography(HPLC) ICP-MS

• Separation of species by use of a column packed with a phase (e.g. resin) that provides either a chemical or physical interaction with the analyte

High-performance liquid chromatography(HPLC) ICP-MS

• Certain species will be retarded during passage through the column such that the time it takes for them to pass through is moderately characteristic of the phase

• The analyte is forced through at high pressure

• Allows less time for species to diffuse within the column (improves resolution)

HPLC

• types of columns – size exclusion - separates on the basis of size

• ion exchange - both anion and cation– As III and As IV - use anion exchange column.

As III comes off column first

HPLC

• HPCL-ICPMS is another transient signal system

• Require the ICP-MS to continuously measure over time and measure the signal as each species comes off the column

Hydride Generation• gaseous sample introduction

• formation of volatile hydride species

• As, Bi, Ge, Pb, Sb, Se, Sn, and Te form volatile hydrides

• more efficient transport to plasma for the elements listed above than in straight solution-mode analysis

• separation of analyte from matrix improves sensitivity and reduces interferences