SPECTROSCOPY (PPT)

• Spectrochemical Methods


  Measurements based on light and other forms of electromagnetic radiation
• Spectrochemical Methods provided the most widely used tools for the elucidation of modern atomic theory
• Spectrophotometry

  (spectroscopy) is any analytical method that uses light for measurement of chemical concentrations
• Spectroscopy

  Originally the study of the interaction between radiation and matter as a function of wavelength (λ)
• Historically, spectroscopy referred to the use of visible light dispersed according to its wavelength, e.g. by a prism
• Spectroscopy

  Dispersion of light as it travels through a triangular prism
• Light

  Can be thought of as a wave or particle
• Wavelength (λ)


  The distance between crests of a wave (m)
• Frequency (ν)


  The number of oscillations per second (Hz)
• Spectral Distribution of Radiant Energy

  Wave Number (cycles/cm)
• Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines
• Beer–Lambert law

  Also known as Beer's law, Lambert–Beer law or Beer–Lambert–Bouguer law, is an empirical relationship that relates the absorption of light to the properties of the material through which the light is travelling
• Beer-Lambert Law

  The law states that there is a logarithmic dependence between the transmission (or transmissivity), T, of light through a substance and the product of the absorption coefficient of the substance, α, and the distance the light travels through the material
• Transmittance


  The fraction of incident light at a specified wavelength that passes through a sample
• Optical density


  A unitless measure of the transmittance of an optical element for a given length at a given wavelength
• Classification of Spectroscopy

  • Electromagnetic spectroscopy
  • Electron spectroscopy
  • Mass Spectrometry (MS)
• Electromagnetic spectroscopy


  Involves interactions of matter with electromagnetic radiation, such as light
• Types of Electromagnetic Spectroscopy

  • Emission spectroscopy
  • Absorption spectroscopy
  • Scattering spectroscopy
• Emission spectroscopy


  The study of electromagnetic radiation spectra given off by atoms or molecules that undergo a transition to a lower energy level
• Emission spectroscopy

  • Fluorescence spectroscopy or fluorometry or spectrofluorometry
  • Flame emission spectroscopy
  • X-ray fluorescence spectroscopy
  • Stellar spectroscopy
• Absorption spectroscopy


  The study of electromagnetic radiation spectra absorbed by atoms or molecules that change energy levels; the atoms usually positioned between a radiation source and the observer
• Types of Absorption Spectroscopy

  • Vibrational spectroscopy - absorption of infrared radiation
  • Atomic absorption - technique for determining the concentration of a particular metal element in a sample
  • UV/visible spectroscopy - absorption of ultraviolet and visible light
  • Mossbauer spectroscopy - Measures the absorption of gamma rays by atoms bound in a solid as a function of gamma-ray energy
• Atomic Absorption Spectroscopy


  It relies heavily on Beer-Lambert law, the electrons of the atoms in the atomizer can be promoted to higher orbitals for an instant by absorbing a set quantity of energy (i.e. light of a given wavelength), this amount of energy (or wavelength) is specific to a particular electron transition in a particular element, and in general, each wavelength corresponds to only one element, giving the technique its elemental selectivity
• Atomic Absorption Spectroscopy

  As the quantity of energy (the power) put into the flame is known, and the quantity remaining at the other side (at the detector) can be measured, it is possible, from Beer-Lambert law, to calculate how many of these transitions took place, and thus get a signal that is proportional to the concentration of the element being measured
• Infrared spectroscopy (IR spectroscopy)

  The subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum, widely used in both research and industry as a simple and reliable technique for measurement, quality control and dynamic measurement, of special use in forensic analysis in both criminal and civil cases, enabling identification of polymer degradation for example, perhaps the most widely used method of applied spectroscopy
• Infrared Spectroscopy

  A beam of infrared light is produced and split into two separate beams, one is passed through the sample, the other passed through a reference which is often the substance the sample is dissolved in, the beams are both reflected back towards a detector, however first they pass through a splitter which quickly alternates which of the two beams enters the detector, the two signals are then compared and a printout is obtained
• Infrared Spectroscopy

  A reference is used to prevent fluctuations in the output of the source affecting the data and to allow the effects of the solvent to be cancelled out (the reference is usually a pure form of the solvent the sample is in)
• Scattering spectroscopy


  Measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles, the scattering process is much faster than the absorption/emission process, one of the most useful applications is Raman spectroscopy
• Raman spectroscopy


  A spectroscopic technique used in condensed matter physics and chemistry to study vibrational, rotational, and other low-frequency modes in a system, it relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range
• Electron spectroscopy


  Involves interactions with electron beams, Auger spectroscopy involves inducing the Auger effect with an electron beam, the measurement typically involves the kinetic energy of the electron as variable
• Mass Spectrometry (MS)


  An analytical technique for the determination of the elemental composition of a sample or molecule, also used for elucidating the chemical structures of molecules, such as peptides and other chemical compounds
• Mass Spectrometry

  MS instruments consist of three modules: an ion source, which splits the sample molecules into ions; a mass analyzer, which sorts the ions by their masses by applying electromagnetic fields; and a detector, which measures the value of an indicator quantity and thus provides data for calculating the abundances of each ion present
• Mass Spectrometry

  The technique has both qualitative and quantitative uses, including identifying unknown compounds, determining the isotopic composition of elements in a molecule, and determining the structure of a compound by observing its fragmentation, other uses include quantifying the amount of a compound in a sample or studying the fundamentals of gas phase ion chemistry, MS is now in very common use in analytical laboratories that study physical, chemical, or biological properties of a great variety of compounds
• Other Types of Spectroscopy

  • Acoustic spectroscopy
  • Dielectric spectroscopy
  • Mechanical spectroscopy
• Spectrophotometry

  The quantifiable study of electromagnetic spectra, more specific than the general term electromagnetic spectroscopy in that spectrophotometry deals with visible light, near-ultraviolet, and near-infrared
• Spectrophotometer


  A photometer (a device for measuring light intensity) that can measure intensity as a function of the color, or more specifically, the wavelength