Spectrophotometry One
The height of the wave
amplitude
The lamp that is used for visual light is _______, and the light used for ultraviolet light is _________.
What is atomization?
The process of converting the analyte to a gaseous form.
To separate the components of a mixture to make the individual components easier to analyze.
Define eluent and eluate.
eluent: what goes into the column
eluate: what comes out of the column
This type of electromagnetic radiation promotes electrons to a higher energy level
Disperses light into its component wavelengths and then selects one wavelength to measure.
What are the parts used in flame atomic absorption spectroscopy?
hollow cathode lamp
flame
monochromator
detector
amplifier
display
Define mobile and stationary phase.
mobile: liquid or a gas that acts as a carrier to push the analyte down the column.
stationary: usually called a column; can be a solid or liquid; analytes interact with the stationary phase differently which causes separation.
Retention time is mainly based on__________.
Vapor pressure
What are the components of a simple spectrophotometer?
light source
monochromator
sample
light detector
display
Define the following three terms:
superposition principle
constructive interference
destructive interference
Superposition principle: two waves can add together give a resulting wave.
Constructive interference: when two waves are completely in phase
Destructive interference: when two waves are completely out of phaseState three differences between atomic and molecular spectroscopy.
• Atomic • UV or visible λ • electron transitions only • atomic orbitals • s « p « d « f • atoms/ions have different transition energies, specific • absorption or emission • Analyte needs to be in vapor phase, atoms • Makes absorption/emission λ very narrow range (~0.1 nm wide
• Molecular • UV, visible, IR, or microwave λ • IR: vibrations (need bonds) • microwave: rotations (need at least two atoms) • UV/Vis: electronic transitions • now some electrons are bonded (or antibonded) in molecular orbitals • s « p, p « p*, etc. • n « p, for example • Sample usually in solution • Broad absorbance λ’
If a column is 25 m long and the plate height is 357 cm, how many plates are there?
There are 70 plates.
To help the molecules that are more similar to the stationary phase come off the column.
What is Beer's Law? Define all variables.
A=ebc
A: absorbance
e: molar absorptivity, the probability that a photon will be absorbedb: path length
c: concentration
True or false: In fluorescence, the emitted photon will have a higher energy than the absorbed photon.
What are three advantages of Fourier-Transform Infrared Spectroscopy?
high throughput
high resolution
fast
What is the Van Deemter equation? Define all variables.
H = A +(B/u) + Cu
H: plate height
A: accounts for multiple path lengths
B: accounts for longitudinal diffusion in the mobile phaseu:linear velocity down the column
What causes overloading and tailing of peaks?
Overloading is caused by too much analyte which causes the concentration to be so high that affects the solubility of the analyte.
Tailing is caused by some solvent or mobile phase interaction with the column is competing with the analyte which prevent the analyte from reaching equilibrium before it moves down the column.
What is the relationship between transmittance and absorbance? If the absorbance is 1, how much of the light is transmitted?
Absorbance is equal to the negative log of transmittance which is equal to the ratio of light out: light in. 10% of the light is transmitted.
Determine the concentration in the following problem.
Ozone has a molar absorptivity of 2700 1/M*cm near 260nm. Find the concentration of ozone (M) in air if a sample has an absorbance of 0.23 in a 10.0 cm cell. Assume the absorbance of air is negligible.
What is 8.5x10^-6 M.
Rank the following in order of increasing sensitivity:
Inductively coupled plasma AES
Flame AA
Inductively coupled plasma mass spectrometry
Graphite Furnace AAFlame AA
Inductively coupled plasma AES
Graphite Furnace AA
Inductively coupled plasma mass spectrometry
What is the general setup for mass spectrometry and what is the difference between hard and soft ionization?
A sample goes into a vacuum where there is an ionization source, separation, and then detection.
Hard ionization gives more energy to the molecule and leads to more fragmentation. Soft ionization gives less energy to the molecule and leads to less fragmentation. Soft also gives a higher abundance of the molecular ion.
Which would come out first on a reverse phase column and on a normal column and why, ascorbic acid at pH 2 or 8? (pKa=4.2)
Normal: pH2 then pH8
Reverse: pH8 then pH2
Ascorbic acid is neutral at pH2meaning it will be less polar; therefore, it will interact longer wherever the nonpolar phase is.