1 / 9

Ultraviolet-Visible S pectroscopy in the Detection of Nitrogen Oxide Air Pollutants

Ultraviolet-Visible S pectroscopy in the Detection of Nitrogen Oxide Air Pollutants. Nitrogen Oxides Pollution. NO x f orms from emissions from vehicles, power plants, and off-road equipment Adverse Effects: Formation of ground level ozone in the presence of heat of sunlight

amma
Télécharger la présentation

Ultraviolet-Visible S pectroscopy in the Detection of Nitrogen Oxide Air Pollutants

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Ultraviolet-Visible Spectroscopy in the Detection of Nitrogen Oxide Air Pollutants

  2. Nitrogen Oxides Pollution • NOxforms from emissions from vehicles, power plants, and off-road equipment • Adverse Effects: • Formation of ground level ozone in the presence of heat of sunlight • Airway inflammation and increased respiratory symptoms in asthma patients Nitrogen Dioxide Ozone

  3. EPA Regulation • EPA sets national standard for nitrogen oxide ambient air concentrations to 53 ppb (annual average) • Decreased by more than 40% since 1980 • Expected to decrease further as mobile source regulations that are taking effect • Ultraviolet-visible (UV-Vis) spectroscopy can determine the concentration of nitrogen oxides.

  4. Ultraviolet-Visible Spectroscopy • Molecular absorption due to excitation of bonding electrons • Can identify functional groups • Can quantify compounds with absorbing groups • The lowest energy transition is the HOMO-LUMO gap in the ground state (DE). • If energy of light exactly matches DE, photon can be absorbed • More conjugated systems have smaller HOMO-LUMO gap • Have lower DE and absorb longer wavelength of light

  5. UV-Vis measurements • Sample dissolved into a non-absorbing solvent • Sample placed in cell • A cell of pure solvent is also analyzed as control • Monochromatic light (190 nm- 800nm) is passed through cell • Intensity of light transmitted is detected • Wavelength varied to test absorption at different energies

  6. Ultraviolet-Visible Spectroscopy • Light transmitted (T) through the sample: T = (I/I0) I=Light intensity I0=Initial light intensity • Beer-Lambert Law of Absorbance (A): A = -log(I / I0) = εbc ε= molar absorptivity (L/mol*cm) b=pathlength of sample cell (cm) c=concentration of compound (mol/L)

  7. Example Absorption spectrum NO3

  8. Gas Chromatography-UV-Vis • Sample evaporated into gas phase • Sample injected into column • Analytes interact with stationary phase in column to different extents • Allows separation of different analytes • Detection by UV-Vis

  9. Advantages/DisadvantagesUV-Vis detection for GC • Advantages: • General indicator of functional groups • Minimal damage to sample • Good quantitation • Using GC eliminates solvent effects • Disadvantages: • Lack of sensitivity & selectivity • Limited to UV-Vis absorbing compounds

More Related