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AS deals with e transfer transition of valence electron between electronic states

AS deals with e transfer transition of valence electron between electronic states. =. =. -. -. =. =. -. -. I. I. I. I. A. A. log. log. T. T. log(. log(. /. /. ). ). o. o. =. =. ε bC. ε bC. µ. µ. A. A. C. C. AAS. A ： absorbance T ： transmittance C ： conc.

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AS deals with e transfer transition of valence electron between electronic states

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  1. AS deals with e transfer transition of valence electron between electronic states

  2. = = - - = = - - I I I I A A log log T T log( log( / / ) ) o o = = εbC εbC µ µ A A C C AAS A：absorbance T：transmittance C：conc. ε：absorpivity b：path length I0 I 吸收值與濃度呈線性關係 AFS Light source 於P0°角看放出之螢光 (P0°乃因有散射) ΦL = k′Φ0C ΦL C  Φ0 hν hν 螢光源與入射光頂角成正比,且與濃度成正比 AES 激發態原子不穩定會降到ground state,而以光的形式放出,放出之光的強度與處於激發態的原子數目有關 (波茲曼係數) Ej Nj/Ni = Pj*e-ΔEi/kT/Pi Ei

  3. Temperature effect on the atomic spectra Boltzmann equation Nj/N0 = gj/g0 * exp(ΔE/RT) AA吸收希望atoms在ground state, AES溫度要高,在excited state’s atoms or ions ↑. Spectral line intensity 原子在excited愈多,強度愈高 (僅電流多點即可) 當conc.很低時,conc. ↑或原子在excited增加,則intensity會增強,最後不再增強而變寬 變寬效應 Iem ∴Iem C (但不會無限制增加) λ

  4. Sequential ICP-AES Instrumentation

  5. Major Components of ICP-AES Sample Delivery System - pump, nebulizer, spray chamber Inductively Coupled Plasma - torch, RF generator Spectrometer - Monochrometer, photomultiplier tube

  6. Sample Delivery System • Nebulizer: • converts sample to aerosol by a jet of gas (compressed Ar) • Common types: • Pneumatic - concentric tube, cross flow • Ultrasonic Concentric-tube pneumatic nebulizer Cross flow nebulizer

  7. Ultrasonic nebulizer with desolvation

  8. Inductively Coupled Plasma • What is a Plasma? • Plasma source provides atomization • Plasma: “a gas-like phase of matter that consists of charged particles” • ICP-AES plasma source is from the carrier gas • Typically argon is used

  9. Drawback • Solid and liquid samples must be prepared so that they can be easily evaporated and ionized by the instrument1 • ICP-AES is a destructive technique, but only a small bit of sample is necessary • Sample introduction into the instrument: the thorn in the side of ICP-AES

  10. Plasma • Plasma source provides atomization • Plasma: “a gas-like phase of matter that consists of charged particles”2 • ICP-AES plasma source is from the carrier gas

  11. Inductively coupled plasma (ICP)…torch design…

  12. Radiofrequency Generator

  13. ICP torch

  14. ICP temperatures

  15. 2 Types of Detection Positions: • Radial Viewing • Axial Viewing Detection Radial Viewing

  16. How to perform Simultaneous Analysis • Simultaneous analysis was carried out until today by using: • polychromators, which are Paschen-Runge optics coupled to high sensitivity detectors known as Photomultiplers (PMT) • Echelle-Grating optics, coupled to Solid State Detectors , (CCD, SCD & CID types), also known as Charge Transfer Devices (CTD’s)

  17. Detail of a Paschen-Runge optics with PMT detectors Diffraction Grating Optical Fibers Photo multipliers

  18. Advantages: • High light throughput • Wide spectral range • Few optical components • Low stray light level • Robust Grating Rowland circle Exit slits Entrance slit Photomultiplier Tubes Photographic Film

  19. X Y PMT SCANNING + PMT

  20. Optics and Detectors

  21. Typical Echellogram

  22. ICP optical emission spectrometryICP-OES • Capable of true simultaneous multielement analysis • Minimal chemical interferences • Spectral interferences overcome with use of alternate lines or intensity corrections on either side of analytical line • Axial and side-on viewing systems available

  23. ICP-OES operation • Variety of sample introduction approaches available (pneumatic nebulizer with ~ 1 mL/min uptake is most common) • Sensitivities better than FAA and often comparable with GFAA when using axial viewing • Varying degrees of automation available

  24. Background Noise Sources • Argon emission lines • Carbon and silicon lines • Oscillation by the plasma itself and oscillations caused during aerosol production and sample delivery Such intensities are practically constant and easily recognized

  25. Poor Detection Limits on Certain Trace Elements • Examples of interferences include: • 40Ar16O on the determination of 56Fe • 38ArH on the determination of 39K • 40Ar on the determination of 40Ca • 40Ar40Ar on the determination of 80Se • Solution: the cold/cool plasma

  26. Limits of Detection Decrease in limits of detection over the course of time using examples of Perkinelmer ICP emission Spectrometers ICP/5000 (1980), Optima 3000 (1993), Optima 3000 XL (1997) All detection limits were determined by the blank method using the statistical factor K = 3 [concentrations in ppb]

  27. DCP

  28. Inductively coupled plasma mass spectrometryICPMS

  29. ICPMS characteristics • “Simultaneous” multielemental analysis • 5-6 orders of magnitude in dynamic range(need fewer standards for calibration) • ppt and even ppq LODs available • Isotopic information available • Spectral interferences occur and involve polyatomic ions or isotopes of other elements • Interferences involving ion optics (e.g., “space charge”) and ionization efficiency are unique to ICPMS

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