Elemental Spectroscopy ICP-OES

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

Theory of Inductively Coupled Plasma Optical Emission Spectroscopy

ICP is shorthand for ICP-AES or ICP-OES. ICP Basics ICP is shorthand for ICP-AES or ICP-OES. What is ICP-AES? It is: Inductively Coupled Plasma Atomic Emission Spectrometer. What is ICP-OES? It is: Inductively Coupled Plasma Optical Emission Spectrometer. Libraries

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

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

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

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

Element Wavelengths Each element has a unique set of wavelengths that it can emit 180nm <-- uv --> 400nm <-- visible --> 800nm 1 2 3 4 5

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

Effect of Temperature on Emission Wavelength increasing -> 200 300 400 600 800 5000 k As Pb Mn Mg Cu Ca Ba Na Li K 3000 k Mg Cu Ca Ba Na Li K 2000 k Ca Na Li K

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

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

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

Plasma Torch

Plasma Zones Plasma Zones observation region (mm) TEMPERATURE ~ 2X NITROUS OXIDE ACETYLENE FLAME 25 6000 k 20 6500 k 15 7000 k RESIDENCE TIME ~ 2MS 8000 k 10000 k sample

Instrument Components There are six basic components to an ICP Sample Introduction Energy Source Spectrometer Detector Electronics Computer and Software

Instrument Components Sample Introduction Energy Source Spectrometer Computer and Software Electronics Detector

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

Instrument Components Sample Introduction the Peristaltic pump the Nebulizer the Spray chamber

Concentric Nebuliser

Instrument Components Energy Source = plasma 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. In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred. Libraries

Instrument Components Energy Source There are three basic parts to the energy source. the Radio frequency generator which generates an oscillating electo-magnetic field at a frequency of 27.12 million cycles per second. This radiation is directed to the Load coil which delivers the radiation to the Torch which has argon flowing through it which will form a plasma in the RF field. In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred. Libraries

Instrument Components Energy Source the Radio Frequency generator the Load coil the Torch In the case of commercially available ICP’s, the ionized gas is argon. Helium plasmas are possible but for cost and performance reasons, argon is preferred. It is possible to form plasmas using molecular gases –O2, N2, CO2– but these require huge amounts of energy and can react chemically with the analytes being measured so inert gases are preferred. Libraries

Plasma Configuration Axial Radial Axial and Radial

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

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

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

Dual View Optics Radial view Axial view

Instrument Components 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. Libraries

Simultaneous Optics – Echelle Spectrometer ICP-Source Detector Prism Grating The iCAP 6000 is echelle spectrometer. A shell spectrometer utilizes a prism and a grating working together To split the spectrum of byte order and wavelengths and end the entire spectrum onto the square or rectangular detector. This impulse cannot take on this alliance demonstrates the design of the echelle spectrometer. In the bottom right of the slide you can see the source which in this case is the ICP . Excited atoms In the ICP emit light at characteristic wavelengths which are focused into the spectrometer. The limited lights passes through a prism and is reflected off a grating to produce the echelle spectrum. As I mentioned in the previous slight the echelle spectrum is a square or rectangular shape and can be captured using a detector that matches exactly the shape of the spectrum. By adopting a national spectrometer design we can use a custom designed solid state detector to analyze the signal .

Instrument Components 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 Shutter Slit (dual) Echelle grating

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

Instrument Components 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. Libraries

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

Instrument Components 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. Libraries

Emission lines appear as points of light 177 nm 800 nm 740 nm 178 nm

Readout Subarray - CID 28 by 28 mm detector element Intensity Wavelength 28 by 28 mm detector element

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

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

Instrument Components 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. Libraries

Instrument Components 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. Libraries

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 Libraries