New Chem

• Three major types of spectrometric methods

  • Optical spectrometry
  • Mass spectrometry
  • X-ray spectrometry
• Atomization


  Elements are converted to gaseous atoms or elementary ions
• Atomic mass spectrometry

  1. Atomization

  2. Converting gaseous atoms to positive ions

  3. Separating ions according to mass-to-charge ratio

  4. Quantitative data obtained by counting separated ions
• 1. ray spectrometry

  Atomization is not required, quantitative results are based on direct measurement of fluorescence, absorption, or emission spectrum
• Atomization methods

  • Inductively coupled plasma
  • Flame
  • Electrothermal
  • Direct-current plasma
  • Electric arc
  • Electric spark
• Atomic absorption spectra

  Consists of resonance lines which are a result of transitions from the ground state to upper levels
• For elements that have several outer electrons, absorption and emission spectra may be much more complex
• Atomic emission spectra

  Excited atoms relax to the ground state giving up their energy as photons of visible or ultraviolet radiation
• Resonance transition


  Transition to or from the ground state
• Resonance lines


  The resulting spectral line which is a result of the transition between an excited electron state and the ground state
• External energy


  Promotes outer electrons from ground state 3s orbitals to 3p, 4p, or 5p excited-state orbitals
• Atomic fluorescence spectra


  Radiant power of fluorescence is measured instead of the attenuated source radiant power
• Atomic fluorescence


  Measured at the same wavelength as the source radiation and is called resonance fluorescence
• Effective line widths

  Narrow lines are highly desirable to reduce interference due to overlapping lines
• To obtain atomic optical spectra and atomic mass spectra, the constituents of the sample must be converted to

  • Gaseous atoms
  • Ions
• The precision and accuracy of atomic methods depend critically on

  • The atomization step
  • The method of introduction of the sample into the atomization region
• Type of Atomizers

  • Flame
  • Electrothermal vaporization (ETV)
  • Inductively coupled argon plasma (ICP)
  • Direct current argon plasma (DCP)
  • Microwave-induced argon plasma (MIP)
  • Laser-induced plasma
  • Glow-discharge plasma
  • Electric arc
  • Electric spark
• Sample introduction system

  To transfer a reproducible and representative portion of a sample into the atomizers with high efficiency and no adverse interference effects
• Sample Introduction Methods

  • Pneumatic nebulization - solution or slurry
  • Ultrasonic nebulization- solution
  • Electrothermal vaporization- solid, liquid, solution
  • Hydride generation- solution of certain elements
  • Direct insertion- solid, powder
  • Laser ablation- solid, metal
  • Spark or arc ablation- conducting solid
  • Glow-discharge sputtering- conducting solid
• Atomization

  Devices fall into 2 classes, continuous and discrete
• Continuous atomizers


  Plasma and flames, samples are introduced in a steady manner
• Discrete atomizers


  Samples are introduced in discontinuous manner using syringe or autosampler, most common is the electrothermal atomizer
• Direct nebulization


  The nebulizer constantly introduces the sample in the form of a fine spray of droplets called an aerosol
• Discrete solution samples


  Introduced by transferring an aliquot of the sample to the atomizer
• Solutions are generally introduced into the atomizer by

  • Pneumatic nebulization - solution or slurry
  • Ultrasonic nebulization- solution
  • Electrothermal vaporization- solid, liquid, solution
• Introduction of solid samples

  • Direct manual insertion
  • Electrothermal vaporization
  • Slurry nebulization
  • Arc, spark, or laser ablation
  • Sputtering in a glow-discharge device
• Laser ablation


  Versatile method of introducing solid samples into atomizer
• Line Sources

  • Hollow cathode lamp
  • Electrodeless-discharge lamps
• Hollow cathode lamp


  Most useful source for atomic absorption spectroscopy, composed of tungsten anode and a cylindrical cathode sealed in a glass tube containing an inert gas at a pressure of 1-5 torr
• Electrodeless-discharge lamps


  Useful source of atomic line spectra, often one to two orders of magnitude more intense than their hollow-cathode counterparts, particularly useful for elements such as As, Se, and Te
• Complete Atomic Absorption Instrument

  • Photometers
  • Spectrophotometers
• Flame Atomic Absorption Spectroscopy


  Provides a sensitive mean for determining 60-70 elements, Disadvantage: only single element can be determined at a time
• Flame atomic absorption


  Quantitative analyses are frequently based on external standard calibration
• Atomic Fluorescence Spectroscopy


  The newest of the optical atomic spectroscopic methods, an external source is used to excite the element of interest
• Laser-excited atomic fluorescence spectrometry


  Capable of extremely low detection limits, particularly when combined with electrothermal atomization, Commercial instrumentation has not been developed, Atomic fluorescence has the disadvantage of being a single-element method unless tunable lasers with their inherent complexities are used
• 1. Ray Fluorescence (XRF)


  A non-destructive analytical technique used to determine the elemental composition of materials
• XRF Qualitative Analysis

  By measuring the energies (determining color) of the radiation emitted by the sample, it is possible which elements are present
• XRF Quantitative Analysis

  By measuring the intensities of the emitted energies (colors), it is possible to determine how much of each element is present in the sample
• 1. Ray Fluorescence Process

  A solid or a liquid sample is irradiated with high energy X-rays from a controlled X-ray tube, The source irradiates a sample and a detector measures the radiation coming from the sample
• Three important properties of the XRF detection system

  • Resolution- ability to distinguish between different energy levels
  • Sensitivity- indicates how efficient incoming photons are counted
  • Dispersion- indicates the ability to separate x-rays with different energies