Applications of UV-Vis Molecular Absorption Spectrometry Chap 14
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NASA's alpha particle X-ray spectrometer (APXS). Image credit: NASA The APXS is designed to study the alpha particles (from radioactive decay) and X-rays emitted by rocks and soils in order to determine their elemental chemistry. Knowing the elemental composition of Martian rocks will provide the scientists with information about the formation of the planet's crust, as well as any weathering that has taken place. Clues as to the nature or weathering on the surface of Mars, will, again raise the issue of whether or not there was surface water.
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Transcript of Applications of UV-Vis Molecular Absorption Spectrometry Chap 14
NASA's alpha particle X-ray spectrometer (APXS).
Image credit: NASA
The APXS is designed to study the alpha particles (from radioactive decay) and X-rays emitted by rocks and soils in order to determine their elemental chemistry. Knowing the elemental composition of Martian rocks will provide the scientists with information about the formation of the planet's crust, as well as any weathering that has taken place. Clues as to the nature or weathering on the surface of Mars, will, again raise the issue of whether or not there was surface water.
Applications of UV-Vis MolecularApplications of UV-Vis Molecular Absorption SpectrometryAbsorption Spectrometry
Chap 14
Spectral data may be plotted with ordinate as:
• absorbance (A)
• percent transmittance (%T)
• log absorbance (log10 A)
Abscissa normally:
• wavelength (nm)
• wavenumber (cm-1)
• frequency (GHz)
ordinate
abscissa
Application to Qualitative Analysis
Table 14.1 Absorption Characteristicsof Some Common Chromophores
Table 14-4 Absorption Characteristics of Aromatics
Fig 6-24 (a)
Partial energy leveldiagram for UV-Vis
absorption in an organicmolecule
Fig 14-1
UV-Vis AbsorptionSpectra for
1,2,4,5 tetrazine
Fig 14-6
Effect ofsolvent onabsorptionspectrum of
acetaldehyde
Transparency: Solvents for the UV-Vis
Table 14-3
Cutoff wavelengths
Solvents: Effect on absorbing system
• Polar solvents tend to “blur” vibrational
features more than nonpolar solvents
• Polar solvents more likely to shift λmax
n → π * blue shiftedblue shifted
• solvation of lone pair lowers energy of n
• ∼ 30 nm when hydrogen-bonding possible
π → π* red shiftedred shifted
• ∼ 5 nm due to attractive polarization
Solvent effects imply that:
UV-Vis is not reliable for qualitative
but excellent for quantitative analysis
Develop Calibration Curve
with Standards
Challenge:
Preparing standards in
same matrix as analyte
Quantitative Analysis
Fig. 14-8Standard Addition Method
Determination of NO2ˉ in water by UV-Vis
M7709.2]NO[ 2
Case (a) : Significant overlap
• Best treated by using aspreadsheet procedure with data obtained at many λ’s.
Case (b) : Little overlap
• Measure Abs of X at λʹ• Measure Abs of Y at λʺ• Solve simultaneousequations for [X] and [Y]
Analogous to Fig. 14-9
Analysis of a Binary Mixture
Analysis of a Binary Mixture of Ti and V
Analysis of a Binary Mixture of Cr2O72- and MnO4
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