instrumental analysis chemistry Study guide
Beam Chopping corrects for flame emission but not for scattering. Can distinguish the signal of the flame from the atomic line at the same wavelength. The higher the absorbance the higher the transmittance.
Intro to IR
Near IR- (0.78 to 2.8 micrometers)
Mid IR- (2.5- 50 micrometers)
Far IR- (50-1000 micrometers)
Most common region used is Mid IR btwn 2.5- 15 micrometers
Mid IR: based on diffracting gratings but now current instrumentation are of Fourier transform type
Far-IR: useful now that Fourier transform instruments are available.
Can measure IR absorption, emission, and reflection in energy in order for a species to absorb IR radiation, it needs to undergo a net change in dipole moment (vibrational/rotational motion)
Rotational Vibrational transition not much energy needed
Liquids and solids intermolecular collisions and interaction that cause broadening lines into a continuum.
IR sources - consist of inert solid and heated electrically to very high temperatures 1500-2000K to get a continuum of radiation.
Nernst Glower- composed of rare earth oxides (ZrO2, Y2O3, and Er2O3) current is passed thru the device so that the device can reach the high temp of 1200-2000K, spectral out in the IR region
Globar source- silicon carbide rod heated to 1300-1500K
Disadvantage to using this is water cooling is required to prevent electrical arching.
Incandescent wire sources- tightly wound spiral michrome wire heated by electrical current to 1100k
IR absorption requirement
1 source of continuous IR radiation
2 IR transducer that’s sensitive
Mercury Arc Source (Far IR) only for Far IR region only has enough radiant power in this region. Quartz jacketed tube containing Hg vapor pressurized greater than 1 atm, electricity passed thru this Hg vapor (pressure emits a continuum of radiation in the far IR region.)
Disadvantage and the advantage to this source is that it only is used for the Far IR region only and can’t be used for any other IR
Intro to IR
Near IR- (0.78 to 2.8 micrometers)
Mid IR- (2.5- 50 micrometers)
Far IR- (50-1000 micrometers)
Most common region used is Mid IR btwn 2.5- 15 micrometers
Mid IR: based on diffracting gratings but now current instrumentation are of Fourier transform type
Far-IR: useful now that Fourier transform instruments are available.
Can measure IR absorption, emission, and reflection in energy in order for a species to absorb IR radiation, it needs to undergo a net change in dipole moment (vibrational/rotational motion)
Rotational Vibrational transition not much energy needed
Liquids and solids intermolecular collisions and interaction that cause broadening lines into a continuum.
IR sources - consist of inert solid and heated electrically to very high temperatures 1500-2000K to get a continuum of radiation.
Nernst Glower- composed of rare earth oxides (ZrO2, Y2O3, and Er2O3) current is passed thru the device so that the device can reach the high temp of 1200-2000K, spectral out in the IR region
Globar source- silicon carbide rod heated to 1300-1500K
Disadvantage to using this is water cooling is required to prevent electrical arching.
Incandescent wire sources- tightly wound spiral michrome wire heated by electrical current to 1100k
IR absorption requirement
1 source of continuous IR radiation
2 IR transducer that’s sensitive
Mercury Arc Source (Far IR) only for Far IR region only has enough radiant power in this region. Quartz jacketed tube containing Hg vapor pressurized greater than 1 atm, electricity passed thru this Hg vapor (pressure emits a continuum of radiation in the far IR region.)
Disadvantage and the advantage to this source is that it only is used for the Far IR region only and can’t be used for any other IR