ICP Theory

44
Elemental Spectroscopy ICP-OES

description

teori icp

Transcript of ICP Theory

Page 1: ICP Theory

Elemental Spectroscopy ICP-OES

Page 2: ICP Theory

2

Content: ICP-OES

• Fundamentals of ICP-OES

• Instrument Components

Page 3: ICP Theory

Theory of Inductively Coupled PlasmaOptical Emission Spectroscopy

Page 4: ICP Theory

4

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.

Page 5: ICP Theory

5

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

Page 6: ICP Theory

6

Atomic Emission Theory

Plasma Polychromator Detector

Inductively Coupled Plasma Atomic Emission Spectrometer

Page 7: ICP Theory

7

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

Page 8: ICP Theory

8

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

Page 9: ICP Theory

9

Element Wavelengths

• Each element has a unique set of wavelengths that it

can emit

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

1 2 3 4 5

Page 10: ICP Theory

10

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

Page 11: ICP Theory

11

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

Page 12: ICP Theory

12

Emission sources

• Flames

• Arcs / Sparks

• Direct Current Plasmas (DCP)

• Inductively Coupled Plasmas (ICP)

Page 13: ICP Theory

13

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

Page 14: ICP Theory

14

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

Page 15: ICP Theory

15

Plasma Torch

Page 16: ICP Theory

16

Plasma Zones

Plasma Zones

sample

6000 k

6500 k

7000 k

8000 k

10000 k

0

15

20

25

observationregion (mm) TEMPERATURE ~ 2X

NITROUS OXIDE ACETYLENE FLAME

RESIDENCE TIME ~ 2MS

Page 17: ICP Theory

17

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

Page 18: ICP Theory

18

Instrument Components

6. Computer and Software

1. Sample Introduction

2. Energy Source

3. Spectrometer

4. Detector5. Electronics

Page 19: ICP Theory

19

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

Page 20: ICP Theory

20

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

Page 21: ICP Theory

21

1. Sample Introduction

i. the Peristaltic pump

ii. the Nebulizer

iii. the Spray chamber

Instrument Components

Page 22: ICP Theory

22

Concentric Nebuliser

Page 23: ICP Theory

23

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

Page 24: ICP Theory

24

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

Page 25: ICP Theory

25

2. Energy Source

i. the Radio Frequency generator

ii. the Load coil

iii. the Torch

Instrument Components

Page 26: ICP Theory

26

Plasma Configuration

• Axial

• Radial

• Axial and Radial

Page 27: ICP Theory

27

Radial or Axial Configuration

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

• Axial design – best sensitivity,

lowest detection limits • Environmental• Chemical

Page 28: ICP Theory

28

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

Page 29: ICP Theory

29

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

Page 30: ICP Theory

30

Dual View Optics

Axial view

Radial view

Page 31: ICP Theory

31

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.

Page 32: ICP Theory

32

Simultaneous Optics – Echelle Spectrometer

ICP-Source

Detector

PrismGrating

Page 33: ICP Theory

33

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

Page 34: ICP Theory

34

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

Page 35: ICP Theory

35

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.

Page 36: ICP Theory

36

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

Page 37: ICP Theory

37

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.

Page 38: ICP Theory

38

Emission lines appear as points of light

177 nm

800 nm 740 nm

178 nm

Page 39: ICP Theory

39

Readout Subarray - CID

Intensity

Wavelength

28 by 28 mdetector element

Page 40: ICP Theory

40

What you get

Full, continuous wavelength coverage; never miss an analyte

Page 41: ICP Theory

41

Power and flexibility

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

future without rerunning samples• Fingerprinting• Matrix or spectral subtraction

Page 42: ICP Theory

42

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.

Page 43: ICP Theory

43

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.

Page 44: ICP Theory

44

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