Organic Analysis (2). What is light? 1. Light as a continuous wave 1. Light as a continuous wave 2. Light as a stream of discrete energy particles (photons).

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Presentation transcript:

Organic Analysis (2)

What is light? 1. Light as a continuous wave 1. Light as a continuous wave 2. Light as a stream of discrete energy particles (photons). 2. Light as a stream of discrete energy particles (photons). Neither theory completely explains all the properties of light. Neither theory completely explains all the properties of light.

“The Wave Theory” Wavelength (λ) and frequency (f) of light.

Electromagnetic radiation spectrum All electromagnetic radiations travel at the speed of light. All electromagnetic radiations travel at the speed of light. Distinguishable by their different wavelengths and frequencies. Distinguishable by their different wavelengths and frequencies. Gamma rays ~ X-rays ~ UV~ Visible ~ IR ~ microwave ~ Radio rays Gamma rays ~ X-rays ~ UV~ Visible ~ IR ~ microwave ~ Radio rays VIBGYOR VIBGYOR Decreasing frequency  Increasing wavelength 

Frequency and wavelength of visible/white light

Coherent vs. Incoherent Light Incoherent light: collection of waves possessing different frequencies and wavelengths. Incoherent light: collection of waves possessing different frequencies and wavelengths. Coherent light: light that is pulsating in unison. Coherent light: light that is pulsating in unison.

Light as a continuous wave f= c λ λ f is frequency (# of crests or troughs), measured as cycles per second. c is speed of light in a vacuum (3 x 10 8 m/s). λ is wavelength, measured as nanometers.

Light as a stream of particles called photons E = hf E = hf E is energy of the photon. f is frequency of radiation h is Planck’s constant (6.626 x J-sec) (6.626 x J-sec)

UV, IR and Visible Spectrophotometry

Spectrophotometry Measures the amount (or quantity) of radiation a particular material absorbs as a function of wavelength / frequency. Measures the amount (or quantity) of radiation a particular material absorbs as a function of wavelength / frequency. Absorption of electromagnetic radiation by chemical substances is selective. Absorption of electromagnetic radiation by chemical substances is selective.

Beers’ Law A= kc A= kc A is absorption of light at a single frequency. k is the proportionality constant. c is the concentration of absorbing material. material. Use Beer’s law for all spectrophotometric applications.

The Spectrophotometer 1. Radiation source (visible, UV or IR) 2. Monochromator (frequency/wavelength selector) 3. Sample holder 4. Detector (convert radiation to electrical signal) 5. Recorder (graph the signal)

Components of a Spectrophotometer.

Which radiation source? Visible, Ultraviolet or Infrared. Visible radiation sources are used for many applications but produce very similar spectra. Visible radiation sources are used for many applications but produce very similar spectra. UV spectra can be similar for many substances. UV spectra can be similar for many substances. IR spectra are different for each substance. IR spectra are different for each substance. IR spectrophotometry is one of the few tests available for specific identification. IR spectrophotometry is one of the few tests available for specific identification.

IR absorption spectra of dichloromethane

Mass Spectrometry Aim a beam of high energy electrons at the sample.  electrons are lost and they acquire a positive charge (“ions”)  decompose into small fragments  magnetic field will separate them according to their mass Results are graphed as a fragmentation pattern.

Forensic applications of mass spectrometry No two substances have the same fragmentation pattern. No two substances have the same fragmentation pattern. Only need grams Only need grams Widest application is in identification of drug mixtures. Widest application is in identification of drug mixtures.

Gas Chromatography-Mass Spectrometry (GC-MS) Gas chromatograph can be linked directly to the mass spectrometer for definitive identification. Gas chromatograph can be linked directly to the mass spectrometer for definitive identification.

Inside the GC-MS

Gas chromatography-mass spectrometry How a GC/MS works How a GC/MS worksHow a GC/MS worksHow a GC/MS works