ICPMS Introduction

ICPMS THE TECHNOLOGY DRIVING ALSICPMS THE TECHNOLOGY DRIVING ALS

ICPMS PEER GROUP

An Introduction to Inductively An Introduction to Inductively Coupled Plasma - Mass Coupled Plasma - Mass Spectrometry (ICP-MS)Spectrometry (ICP-MS)

1st August 2003

22ICPMS THE TECHNOLOGY DRIVING ALSICPMS THE TECHNOLOGY DRIVING ALS

What Is ICP-MS?What Is ICP-MS?


What is ICP-MS?What is ICP-MS?

ICP-MS is a technique which allows the analyst to identify and quantify the atomic/elemental make up of a material.

It provides a high speed, multi-element analysis.

It offers lower detection limits than ICP-OES for most elements.


How does an ICP-MS Work?How does an ICP-MS Work?

A n a lytica l R e a d O ut

D e te ctio n S ys tem(M a ss S p e c trom e te r)

Io n iza tion S ou rce(In d u ctive ly C o u p le d P la sm a)

S a m p le In tro du c tio n S ys tem(N e b u liza tio n )

Basic Components of an ICP-MS System


Sample Introduction SystemSample Introduction System

PurposePurpose

To take solution samples and transport To take solution samples and transport them as a homogenous aerosol to the them as a homogenous aerosol to the plasma.plasma.



Sample Introduction Sample Introduction System Main System Main ComponentsComponents

Peristaltic PumpPeristaltic Pump

NebulizerNebulizer

Spray ChamberSpray Chamber

Plasma Torch and Plasma Torch and InjectorInjector



Peristaltic PumpPeristaltic Pump

Ensures constant Ensures constant flow rate of sample. flow rate of sample.

Allows regulation of Allows regulation of uptake rate.uptake rate.


Sample Introduction SystemSample Introduction SystemNebulizer

Mixes Argon gas with sample solution to produce a mist or aerosol.

Many different nebulizers are available, each with their own advantages and disadvantages depending upon the application.

Meinhard Nebulizer



Spray ChamberSpray Chamber Separates out droplets by size.Separates out droplets by size. Large droplets removed by Large droplets removed by

collision with spray chamber collision with spray chamber walls.walls.

Only droplets of the correct Only droplets of the correct size and velocity will make it size and velocity will make it through the spray chamber to through the spray chamber to the torch.the torch.

Only around 2-3% of the Only around 2-3% of the originally aspirated solution originally aspirated solution reaches the torch.reaches the torch.



Plasma Torch and Injector.

Plasma gas flow ~15 l/min, reacts with RF field to form the plasma.

Auxiliary gas flow controls position of plasma relative to the torch.

Nebulizer gas flow provides gas flow to the nebulizer and carries the sample aerosol into the plasma.


Ionization SourceIonization Source

PurposePurpose

The heat energy of the plasma firstly The heat energy of the plasma firstly dries the sample aerosol, and then dries the sample aerosol, and then strips electrons from the elements to strips electrons from the elements to create ions.create ions.



What is a plasma?

A plasma is a stream of highly ionized gas.A plasma is electrically conductive.A plasma is affected by magnetic fields.Operate at ~ 6-10000 K.Fourth state of matter.Most common state of matter in the universe.



How do we make Plasmas?


Ionization SourceIonization SourceHow Do We Make Plasmas?

A - Argon gas flows through three concentric tubes.

B - A copper coil, called the load coil, surrounds the top end of the torch and is connected to a radio frequency generator. When Rf power (typically 700-1500 Watts) is applied to the load coil, A/C oscillates at a rate corresponding to the frequency of the generator (27 or 40 megahertz) which causes Rf electric and magnetic fields to be set up.

C - With Argon flowing through the torch, a Tesla spark is applied causing some electrons to be stripped from the Argon atoms.



How Do We Make Plasmas? - Continued

D - Stripped electrons are then caught in the magnetic field and accelerated. The high energy electrons collide with Argon atoms stripping off still more electrons and propagating the chain reaction. (adding energy to the electrons by the use of a coil is called inductively coupling)The Inductively Coupled Plasma (ICP) discharge is sustained as long as the Rf energy is transferred through the inductive coupling process.E – The sample aerosol-carrying nebulizer flow distorts the plasma.



Plasma Processes• Desolvation

• Remove solvent from sample.

• Vapourization• Decompose individual

particles into a gas of individual molecules.

• Atomization• Dissociate molecules

into atoms.

• Ionization• Removal of electron



Why use Plasmas in Analytical Instruments?

Higher plasma temperatures improve excitation/ionization.

Flames and Furnaces have upper ranges of 3000C, plasmas easily attain 6000C or higher.

The higher ICP temperatures reduce many chemical interferences.



Condition of the sample in the plasma• Most elements are 90% ionized in the 6000oC environment of the

plasma. Exceptions to this are: As - 52% Se - 33% S - 14% F - 0.0009%

• Singly charged positive ions predominate. • There are some small doubly charged populations that exist, the

worst case is Ba++.



Why use Plasmas in Analytical Instruments?

Low background.

Low detection limits.

Multielement technique.

Extended calibration range.


Detection SystemDetection System

PurposePurpose

The mass spectrometer receives an ion stream The mass spectrometer receives an ion stream from the plasma. It then focuses the stream from the plasma. It then focuses the stream and filters it so that only ions with a certain and filters it so that only ions with a certain mass-to-charge (m/z) ratio are allowed to mass-to-charge (m/z) ratio are allowed to reach the detector.reach the detector.

The ion stream hits the detector, which The ion stream hits the detector, which generates an electrical signal which is used generates an electrical signal which is used to determine how many hits/counts it has to determine how many hits/counts it has received. received.



The Mass Spectrometer consists of The Mass Spectrometer consists of several important sub-components:several important sub-components: Ion extraction system (Interface)Ion extraction system (Interface) Ion Focusing System (Ion Optics)Ion Focusing System (Ion Optics) Vacuum SystemVacuum System Mass FilterMass Filter DetectorDetector



The Interface

The interface is the region between the plasma and the central chamber of the Mass Spectrometer

• The main function of the interface region is to extract ions from the central channel of the plasma and direct them to where the mass separation will take place.



The Interface and Vacuum System Ion extraction is achieved through use of vacuum pumps. A mechanical pump evacuates the region between the sampler and skimmer cone. This serves to pull ions from the plasma through the sampler orifice.The main chamber is evacuated using powerful turbo pumps which draw the ion stream from the interface region through the skimmer orifice.

ICP

Sampler cone

Skimmer cone

Main Chamber



The Vacuum System - Turbo Pumps The Vacuum System - Turbo Pumps

The turbo pump has two important purposes:The turbo pump has two important purposes:

The first is to assist in ion extraction.The first is to assist in ion extraction.The second is to remove neutral species The second is to remove neutral species from the main chamber so as to provide a from the main chamber so as to provide a collision free path for the ion stream.collision free path for the ion stream.


Detection SystemDetection SystemIon OpticsIon Optics

The function of the ion optics is The function of the ion optics is to focus the ions extracted by to focus the ions extracted by the interface and direct them the interface and direct them into the mass filter. into the mass filter.

Using the electric field from Using the electric field from specially shaped metal pieces specially shaped metal pieces (ion lenses), the ions are (ion lenses), the ions are pushed into the mass filter. pushed into the mass filter. These electric fields are These electric fields are created by applying an electric created by applying an electric current or voltage to the lens.current or voltage to the lens.

InterfaceIon OpticsMass Filter

Mass Filter

Rf Only Filter

Differential Aperture Photon

Stop

SamplerSkimmer

Cylinder Lens (E1)


Detection SystemDetection SystemIon OpticsIon Optics

The Perkin Elmer ELAN series of instruments that ALS The Perkin Elmer ELAN series of instruments that ALS Chemex uses has an adjustable voltage lens called an Chemex uses has an adjustable voltage lens called an AUTOLENS.AUTOLENS.

The Autolens is cylindrical in shape.The Autolens is cylindrical in shape.

As the ion stream passes through the Autolens, the applied As the ion stream passes through the Autolens, the applied voltage focuses the analyte of interest.voltage focuses the analyte of interest.

The voltage applied to the Autolens is computer controlled The voltage applied to the Autolens is computer controlled and adjusts to an optimal voltage for each particular analyte.and adjusts to an optimal voltage for each particular analyte.


Detection SystemDetection SystemMass FilterMass Filter

After the ion stream is focused by the autolens, it then enters After the ion stream is focused by the autolens, it then enters the quadrupole mass filter.the quadrupole mass filter.

A quadrupole is a set of four gold plated ceramic rods A quadrupole is a set of four gold plated ceramic rods which are set in a rigid mount.which are set in a rigid mount.

The rods are charged, with opposing rods having the same The rods are charged, with opposing rods having the same charge as shown below. charge as shown below.

+

-

+++

+


Detection SystemDetection SystemMass Filter

When the charge on the rods alternates at a certain frequency, only ions with a particular mass-to-charge ratio spiral perfectly through the quadrupole and reach the detector.All other masses are either lost from the quadrupole or collide with the negative rods.By changing the frequency of the alternating charge, ions of different masses can be analyzed.



Quadrupole from a Perkin Elmer ELAN 6000Quadrupole from a Perkin Elmer ELAN 6000

Detector

Quadrupole Rodset


Detection SystemDetection SystemThe DetectorThe Detector

After the analyte ions have passed through the mass filter After the analyte ions have passed through the mass filter they reach the detector.they reach the detector.

The detectors used in the Perkin Elmer ELAN series are The detectors used in the Perkin Elmer ELAN series are impact sensitive electron multipliers. (shown below)impact sensitive electron multipliers. (shown below)


Detection SystemDetection SystemThe Detector

Ions exiting the quadrupole are directed (via an electric field) on to an impact sensitive film.

When the ions hit the film they dislodge electrons on the outer layer of the film.

The dislodged electrons then make their way down a series of dynodes, with electron multiplication occurring at each successive dynode.

This is process is called electron cascading.




D e te ctio n S ys tem(S p e c tro m e te r)

E xc ita tion S ou rce(In d u ctive ly C o u p le d P la sm a)


Basic Components of an ICP-OES System


Analytical Read OutAnalytical Read Out

The amplified current

from the electron

multiplier is recorded.

The system software

then converts the

recorded signal to an

easily understandable

form, such as number

of counts or

concentration.


Analytical Read OutAnalytical Read Out

208Pb

52.4% Abundant

22.1% Abundant207Pb206Pb

24.1% Abundant


Analytical Read OutAnalytical Read OutFrom the analysis, we are able to calculate the intensity of the signal at a particular mass.

By running standards of known concentrations, we then create a calibration curve.

Given an unknown sample, we are able to determine the intensity of the signal, and then interpolate the concentration of a particular element.

Sb 121 - Calibration Chart

0

500000

1000000

1500000

2000000

2500000

0 5 10 15

Concentration (ppb)

Sig

na

l In

ten

sit

y


Analytical ReadoutAnalytical Readout

INTERERENCESINTERERENCES

When analysing the data, one needs to be When analysing the data, one needs to be aware of interferences. Three types of aware of interferences. Three types of interference occur:interference occur:

Isobaric interferences Isobaric interferences Polyatomic interferencesPolyatomic interferences Doubly charged ion interferences Doubly charged ion interferences



ISOBARIC INTERFERENCESISOBARIC INTERFERENCES

• Isobaric interferences arise when the analyte Isobaric interferences arise when the analyte mass coincides with an isotope of a different mass coincides with an isotope of a different element, for example, the major isotope of zinc at element, for example, the major isotope of zinc at mass 64 has an interference from a minor nickel mass 64 has an interference from a minor nickel isotope.isotope.

• In cases like this, it is best to read one of the In cases like this, it is best to read one of the other zinc isotopes that is free from interference.other zinc isotopes that is free from interference.



POLYATOM IC INTERFERENCESPOLYATOM IC INTERFERENCES

• Conditions in the plasma sometimes allow for the Conditions in the plasma sometimes allow for the formation of polyatomic ions. This occurs most formation of polyatomic ions. This occurs most often with elements that are in high abundance often with elements that are in high abundance such as argon, oxygen and chlorine. Examples such as argon, oxygen and chlorine. Examples of polyatomic interferences are :of polyatomic interferences are :

• Ar-Cl on mass 75 (As) and 77 (Se)Ar-Cl on mass 75 (As) and 77 (Se)• Cl-O on mass 51 (V)Cl-O on mass 51 (V)



DOUBLY CHARGED ION INTERFERENCES

• Conditions in the plasma can also permit the formation of doubly charged ions. This is a problem in that the quadrupole filters according to the mass-to-charge ratio, not mass alone. So, this means that Ba++ (m/z=138/2) will pass through the quadrupole at the same time as Ga+ (m/z=69/1).

* Interferences from polyatomic and doubly charged ions can be minimised by optimising the gas flow and lens voltage.


ICPMS in SummaryICPMS in SummaryIN SHORT, an ICPMS works in the

following way:

The ICP (Plasma) atomizes, and then ionizes the introduced sample.

The sample stream is then focused by an ion lens and passes through a mass filter.

The ion stream then hits the detector.

The number of hits or counts is then converted to a concentration of analyte by the system computer.

ICPMS Introduction

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