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Elemental Spectroscopy ICP-OES. 2 Content: ICP-OES Fundamentals of ICP-OES Instrument Components.

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Presentation on theme: "Elemental Spectroscopy ICP-OES. 2 Content: ICP-OES Fundamentals of ICP-OES Instrument Components."— Presentation transcript:

1 Elemental Spectroscopy ICP-OES

2 2 Content: ICP-OES Fundamentals of ICP-OES Instrument Components

3 Theory of Inductively Coupled Plasma Optical Emission Spectroscopy

4 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.

5 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

6 6 Atomic Emission Theory Plasma Polychromator Detector Inductively Coupled Plasma Atomic Emission Spectrometer

7 7 Excitation 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

8 8 Atomic Emission Photon Excited State Ground State + hv A photon of light is emitted when an electron falls from its excited state to its ground state

9 9 Element Wavelengths Each element has a unique set of wavelengths that it can emit 180nm800nm400nm

10 10 Atomic Emission explained Atomic Emission – the wavelength regions Lower wavelengths are shorter and have more energy, higher wavelengths e.g. in the Visible region, are longer and have less energy

11 11 Effect of Temperature on Emission Wavelength increasing -> 2000 k 3000 k 5000 k CaNaLi K Ca NaLi K K Na CaBa CuMg CuAsPbMn

12 12 Emission sources Flames Arcs / Sparks Direct Current Plasmas (DCP) Inductively Coupled Plasmas (ICP)

13 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

14 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

15 15 Plasma Torch

16 16 Plasma Zones sample 6000 k 6500 k 7000 k 8000 k k observation region (mm) TEMPERATURE ~ 2X NITROUS OXIDE ACETYLENE FLAME RESIDENCE TIME ~ 2MS

17 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

18 18 Instrument Components 6.Computer and Software 1.Sample Introduction 2.Energy Source 3.Spectrometer 4.Detector 5.Electronics

19 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

20 20 1.Sample Introduction There are three basic parts to the sample introduction system. i. the Peristaltic pump draws up sample solution and delivers it to ii.the Nebulizer which converts the solution to an aerosol that is sent to iii. the Spray chamber which filters out the large, uneven droplets from the aerosol. Instrument Components

21 21 1.Sample Introduction i.the Peristaltic pump ii.the Nebulizer iii. the Spray chamber Instrument Components

22 22 Concentric Nebuliser

23 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

24 24 2.Energy Source There are three basic parts to the energy source. i. the Radio frequency generator which generates an oscillating electo- magnetic field at a frequency of million cycles per second. This radiation is directed to ii.the Load coil which delivers the radiation to iii. the Torch which has argon flowing through it which will form a plasma in the RF field. Instrument Components

25 25 2.Energy Source i.the Radio Frequency generator ii.the Load coil iii. the Torch Instrument Components

26 26 Plasma Configuration Axial Radial Axial and Radial

27 27 Radial or Axial Configuration Radial design – Robust, fewer interferences Petrochemical Metallurgy Axial design – best sensitivity, lowest detection limits Environmental Chemical

28 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

29 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

30 30 Dual View Optics Axial view Radial view

31 31 Instrument Components 3.Spectrometer Once 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.

32 32 Simultaneous Optics – Echelle Spectrometer ICP-Source Detector Prism Grating

33 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 Focusing Mirror Prism Collimating Mirror Shutter Slit (dual) Echelle grating

34 34 iCAP Optics - Polychromator High resolution 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 C

35 35 Instrument Components 4.Detector Now 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.

36 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

37 37 Instrument Components 4.DetectorThe 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.

38 38 Emission lines appear as points of light 177 nm 800 nm740 nm 178 nm

39 39 Readout Subarray - CID Intensit y Wavelength 28 by 28  m detector element

40 40 What you get Full, continuous wavelength coverage; never miss an analyte

41 41 Power and flexibility Rapid qualitative analysis Ability to analyze for elements in the future without rerunning samples Fingerprinting Matrix or spectral subtraction

42 42 Instrument Components 5.Electronics The 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.

43 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.

44 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


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