Discuss instrument design Plasmas, Arcs or Sparks ...faculty.uml.edu/david_ryan/84.314/Instrumental...
Transcript of Discuss instrument design Plasmas, Arcs or Sparks ...faculty.uml.edu/david_ryan/84.314/Instrumental...
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Chapter 10: Emission Spectroscopy Using Plasmas, Arcs or Sparks
– Inductively Coupled Plasma (ICP)– Direct Current Plasma (DCP)– Arcs and Sparks
Still talking about Optical Atomic SpectrometryFocus primarily on plasmas as sourcesDiscuss instrument designand other considerations
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Sources
• In AE the plasma, flame, arc or spark act as the device for atomization and the source to excite the atoms – no light source needed
• High temperatures generate a significant population of excited state atoms from the Boltzmann distribution
• High temp. sources also remove or burn off many potentially problematic molecular species that might result in interferences
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ICP Torch with sample
introduction system (nebulizer
and spray chamber)
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ICP Temps.
The viewing area for each
element is typically
reported as mm above
the load coil
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Direct CurrentPlasma (DCP)Torch
Lab will involveuse of DCP formultielementanalysis
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Wavelength Selection Detection
• Same concepts as Molecular Spectroscopy• Grating and prism based monochromators• Need very high resolution because atomic
lines are narrow & many – overlaps possible• Can do simultaneous multi-element analysis• Two types of general approaches:
– Fixed optical arrangements = direct reading spec– Slew scanning or sequential analysis
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High resolution Echelle Polychromator as used in the DC Plasma AE Spectrometer & other instruments
Aperature plate consisting of multipleexit slits where PMTdetectors can be arranged for multi-element detection
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Another diagram of an Echelle optical system employing aCharge Injection Transducer (i.e. a 2D array based detector)
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Another plasma polychromatorsystem employing the classicRowland circle design
entrance slit, grating &exit slits are located ina circular arrangement
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Slew-Scan spectrometer scans rapidly between lines& slowly near lines of interest
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Analytical considerations• More than one emission line
can be used for analytical purposes– To avoid interferences– To reduce sensitivity
• Calibration curves highly linear – large dynamic range
• Internal standards sometimes used to remove matrix interferences
• Spectrochemical buffers added to samples & standards to control ionization
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ICP Calibrationcurves forseveral metals,log-log plots
note linearityover at least2 orders ofmagnitude
Tl & Nb linesare curvedpossibly due toimproper back-ground correction
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Four types of samplesare compared here toshow the lack of anyeffect for matrix specieslike Na, Ca & Mg vs.distilled water
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Electrodes for arc & spark emission spectrometrysamples are coated on surface or placed wells
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Eagle Mounting usedhistorically for arc &spark emission with photographic detection
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Photographic detection givesline spectra
Lines can becompared witha densitometerfor intensity &semi-quantitativeanalysis
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Direct readingflame photometerfor K, Li & Na
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Chapter 11: Atomic Mass Spectrometry (Inorganic MS)
• Mass Spectrometers• ICP-MS• Spark Source MS• Glow-Discharge MS• Elemental Surface Analysis by MS• Laser Ablation ICP-MS
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Atomic Mass Spec processes• Atomization (sample intro)• Conversion to ions• Separation based on m/z ratio• Detection
In other forms of MS (GC-MS or MS of organic compounds), sample introduction does not involve making atoms, just getting molecules into the high vacuum system
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Basic MSdesigncomponents
Note highvacuum