Elemental Spectroscopy ICP-OES

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Content: ICP-OES

• Fundamentals of ICP-OES

• Instrument Components

Theory of Inductively Coupled PlasmaOptical Emission Spectroscopy

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ICP is shorthand for ICP-AES or ICP-OES.

What is ICP-AES? It is:Inductively Coupled Plasma Atomic Emission Spectrometer.

ICP Basics

What is ICP-OES? It is:Inductively Coupled Plasma Optical Emission Spectrometer.

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Atomic Emission Theory

• Atomic emission spectroscopy (AES or OES) uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration

• Analyte atoms in solution are aspirated into the excitation region where they are desolvated, vaporized, and atomised by a plasma

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Atomic Emission Theory

Plasma Polychromator Detector

Inductively Coupled Plasma Atomic Emission Spectrometer

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Excitation

E x c i t e d S t a t eG r o u n d S t a t e

ER e l a x a t i o n

E x c i t a t i o n

Electrons can be in their ground state (unexcited) or enter one of the upper level orbitals when energy is applied to them. This is the excited state

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Atomic Emission

PhotonExcited State Ground State

+ hv

A photon of light is emitted when an electron falls from its excited state to its ground state

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Element Wavelengths

• Each element has a unique set of wavelengths that it

can emit

180nm 800nm400nm <-- visible --><-- uv -->

1 2 3 4 5

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Atomic Emission explained

• Atomic Emission – the wavelength regions

Spectral Region

Vacuum UV Ultra-Violet Visible Near IR

Wavelength = nm 160 190 360 760 900

Lower wavelengths are shorter and have more energy, higher wavelengths e.g. in the Visible region, are longer and have less energy

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Effect of Temperature on Emission

Wavelength increasing ->

2000 k

3000 k

5000 k

Ca Na Li

K

Ca

Na Li

K

KLiNa

Ca Ba

Ba

CuMg

Mg CuAs Pb Mn

200 300 400 600 800

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Emission sources

• Flames

• Arcs / Sparks

• Direct Current Plasmas (DCP)

• Inductively Coupled Plasmas (ICP)

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Inductively Coupled Plasma (ICP) – source, plasma formation, plasma zones

• Quartz torch surrounded by induction coil

• Magnetic coupling to ionized gas

• High temperature – equivalent to 10,000k

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Plasma Advantages

• High Temperature – allows for full dissociation of sample components

• Argon is Inert – non reactive with sample• Linearity – analysis of samples from ppb to ppm range in the same

method• Matrix tolerance – robust and flexible design with Duo and Radial

options

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Plasma Torch

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Plasma Zones

Plasma Zones

sample

6000 k

6500 k

7000 k

8000 k

10000 k

0

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observationregion (mm) TEMPERATURE ~ 2X

NITROUS OXIDE ACETYLENE FLAME

RESIDENCE TIME ~ 2MS

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Instrument Components

There are six basic components to an ICP

1. Sample Introduction

2. Energy Source

3. Spectrometer

4. Detector

5. Electronics

6. Computer and Software

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Instrument Components

6. Computer and Software

1. Sample Introduction

2. Energy Source

3. Spectrometer

4. Detector5. Electronics

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1. Sample Introduction The sample solution

cannot be put into the energy source directly. The solution must first be converted to an aerosol.

The function of the sample introduction system is to produce a steady aerosol of very fine droplets.

Instrument Components

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1. Sample Introduction

There are three basic parts to the sample introduction system.

i. the Peristaltic pumpdraws up sample solution and delivers it to

ii.the Nebulizerwhich converts the solution to an aerosol that is sent to

iii. the Spray chamberwhich filters out the large, uneven droplets from the aerosol.

Instrument Components

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1. Sample Introduction

i. the Peristaltic pump

ii. the Nebulizer

iii. the Spray chamber

Instrument Components

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Concentric Nebuliser

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2. Energy Source The sample aerosol

is directed into the center of the plasma. The energy of the plasma is transferred to the aerosol.

The main function of the energy source is to get atoms sufficiently energized such that they emit light.

Instrument Components

= plasma

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2. Energy Source

There are three basic parts to the energy source.

i. the Radio frequency generatorwhich generates an oscillating electo-magnetic field at a frequency of 27.12 million cycles per second. This radiation is directed to

ii.the Load coilwhich delivers the radiation to

iii. the Torchwhich has argon flowing through it which will form a plasma in the RF field.

Instrument Components

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2. Energy Source

i. the Radio Frequency generator

ii. the Load coil

iii. the Torch

Instrument Components

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Plasma Configuration

• Axial

• Radial

• Axial and Radial

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Radial or Axial Configuration

• Radial design – Robust, fewer interferences • Petrochemical• Metallurgy

• Axial design – best sensitivity,

lowest detection limits • Environmental• Chemical

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Axial Advantage

• Much more light available. This gives you the opportunity to achieve Lower Detection Limits than Radial Plasma

• BUT- unfortunately, you also get...

• More Matrix Interferences

• Slightly Reduced Dynamic Range

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Duo viewing

• Axial view plasma looks down the central channel of the plasma, this provides the best sensitivity and detection limits

• DUO – this is an axially configured plasma that also allows for radial view through a hole in the side of the axial torch

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Dual View Optics

Axial view

Radial view

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Instrument Components

3. SpectrometerOnce the atoms in a sample have been energized by the plasma, they will emit light at specific wavelengths. No two elements will emit light at the same wavelengths.

The function of the spectrometer is to diffract the white light from the plasma into wavelengths.

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Simultaneous Optics – Echelle Spectrometer

ICP-Source

Detector

PrismGrating

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Instrument Components

3. Spectrometer

There are several types of spectrometers used for ICP. Regardless of type, all of them use a diffraction grating.

For the iCAP, an echelle spectrometer is used. The components in this spectrometer are shown at left.

CID Detector

FocusingMirror

Prism

CollimatingMirror

Shutter

Slit(dual)

Echellegrating

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iCAP Optics - Polychromator

• High resolution• 7pm @ 200nm

• High image quality & low stray light• aberration compensation over whole CID

• High energy throughput• double pass prism

• All lines on chip• anamorphic magnification

• Stable• thermal insulation & heater control to 0.10C

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Instrument Components

4. DetectorNow that there are individual wavelengths, their intensities can be measured using a detector. The intensity of a given wavelength is proportional to the concentration of the element.

The function of the detector is to measure the intensity of the wavelengths.

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Charge Injection Device Array Detector

• >291,600 addressable silicon-based

photo detectors

• Full Spectrum Imaging

• Random Access Integration (RAI)

• Inherently Anti-blooming

– Non Destructive Readout (NDRO), allows the S/N ratio to be improved by repeatedly reading each pixel

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Instrument Components

4. Detector The detector is a silicon chip that is composed of many individual photo-active sections called “picture elements”. These picture elements, or pixels, will build up charge as photons impinge on them. Individual pixels are of a size such that they can be used to measure individual wavelengths.

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Emission lines appear as points of light

177 nm

800 nm 740 nm

178 nm

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Readout Subarray - CID

Intensity

Wavelength

28 by 28 mdetector element

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What you get

Full, continuous wavelength coverage; never miss an analyte

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Power and flexibility

• Rapid qualitative analysis• Ability to analyze for elements in the

future without rerunning samples• Fingerprinting• Matrix or spectral subtraction

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Instrument Components

5. ElectronicsThe output from the detector is processed by a set of electronics. The electronics control the detector as well as collect the readings from the pixels

The function of the electronics is to measure and process the output of the detector.

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Instrument Components

6. Computer and Software The software, via a computer, controls and runs the instrument. Not only are measurements made but the other five components of the instrument are controlled and monitored by the computer and software,

The function of the computer and software is to operate, monitor, and collect data from the instrument.

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ICP Basics

ICP Performance

• Typical analysis time for ICP is ~2-3 minutes. This includes flush time, multiple repeats, printing, etc. (Analysis time is independent of the number of elements being determined)

• Typical precision, amongst repeats within an analysis, is ~0.5%

• Typical drift is ≤ 2% per hour

• Typical detection limits are ~ 1-10 parts per billion