INSTRUMENTAL ANALYSIS ACS EVALUATION EXAMS
QUESTIONS AND ANSWERS SURE A+
✔✔Fourier Transform - ✔✔Converts signal from time domain to a frequency domain,
Helps separate signal from noise.
breaks down signal into frequencies to allow the isolation of noise
✔✔signal averaging: - ✔✔taking multiple measurements to improve S/N.
Q: Effect on S/N? A: S/N increases as √n (n = number of measurements). Takes more
time tho
✔✔Wave Properties (frequency, wavelength, velocity, amplitude). - ✔✔-wavelength (λ):
Distance between peaks of a wave.
-frequency (ν): Number of waves per second.
-velocity (c): Speed of light (3.0 × 10⁸ m/s).
-amplitude: Height of the wave (related to intensity).
c=λν
E=hν
✔✔What is a photon?
Energy equation? - ✔✔- A particle of light with energy.
E=hν, Energy is proportional to frequency.
✔✔Electromagnetic Spectrum
What do different regions do? - ✔✔Radio → microwave → IR → visible → UV → X-ray
→ gamma.
- Cause different transitions (electronic, vibrational, rotational)
increasing freq as well when increasing energy
✔✔types of scattering of radiation - ✔✔Can be used to determine the size of particles
• Rayleigh scattering: greater scattering of
shorter wavelengths
• Scattering by large molecules is different indifferent direction; called Mie scattering
✔✔Polarization of light - ✔✔Restricting the vibration of the light wave to a single plan
✔✔What does quantized energy mean? - ✔✔bound systems (atoms/molecules) have
discrete, quantized energy levels, meaning they can only exist in specific states rather
than a continuous range of energies.
Energy exists in specific levels (not continuous)
✔✔Fluorescence vs Phosphorescence - ✔✔- fluorescence: Fast emission (very quick).
- phosphorescence: Slower emission (lasts longer).
, ✔✔Components of Optical Instruments: Radiation Sources - ✔✔continuous sources:
Emit a wide range of wavelengths. (e.g., Tungsten lamp (visible, 320-2400 nm),
Deuterium lamp (UV, 190-380 nm), Xenon arc lamp (broad, 200-1000 nm)
line sources: Emit specific wavelengths.
(e.g., hollow cathode lamps, electrodeless discharge lamps, lasers).
✔✔Components of Optical Instruments:Wavelength Selectors
components of them are? - ✔✔Allow certain wavelengths through.
- filters: Absorption filters, Interference filters
- monochromator (Device that isolates one wavelength, can be by Prism or Grating
components;
~resolution: Ability to separate close wavelengths.
~bandwidth: Range of wavelengths passed.
~dispersion: Separation of light into wavelengths.
✔✔Components of Optical Instruments: Radiation detectors - ✔✔Photomultiplier Tubes
(PMT): Very sensitive detectors for low light (amplifies signal).
Photodiodes: Convert light into current.
CCD (Charge-Coupled Device): Detects many wavelengths at once (like a camera
sensor).
IR Detectors:
- thermocouples/bolometers: Detect heat (infrared radiation).
✔✔Beer's law and limitations - ✔✔A=εbc
*Absorbance is proportional to concentration*
3 main limitations:
- fundamental limitation: At high concentration, molecules interact → changes
absorptivity.
- chemical limitation: If analyte is in equilibrium, concentration is not accurate.
- instrumental deviation: Stray light and non-monochromatic light.
✔✔Stray Radiation and Non-Monochromatic Radiation - ✔✔Stray Radiation: Extra
unwanted light reaching detector. Makes absorbance LOWER than expected (negative
deviation).
🔹 Non-Monochromatic Radiation:
Beer's Law assumption is that Light is one wavelength (monochromatic), if it's not
Absorbance decreases.
to fix, Measure at λmax (max absorbance).
✔✔Absorption vs interference filter - ✔✔Absorption: wider range
interference: (narrower, more precise)
✔✔Instrument Types for UV/Vis : readout - ✔✔Filter Photometer
Single-Beam Spectrophotometer ⭐
QUESTIONS AND ANSWERS SURE A+
✔✔Fourier Transform - ✔✔Converts signal from time domain to a frequency domain,
Helps separate signal from noise.
breaks down signal into frequencies to allow the isolation of noise
✔✔signal averaging: - ✔✔taking multiple measurements to improve S/N.
Q: Effect on S/N? A: S/N increases as √n (n = number of measurements). Takes more
time tho
✔✔Wave Properties (frequency, wavelength, velocity, amplitude). - ✔✔-wavelength (λ):
Distance between peaks of a wave.
-frequency (ν): Number of waves per second.
-velocity (c): Speed of light (3.0 × 10⁸ m/s).
-amplitude: Height of the wave (related to intensity).
c=λν
E=hν
✔✔What is a photon?
Energy equation? - ✔✔- A particle of light with energy.
E=hν, Energy is proportional to frequency.
✔✔Electromagnetic Spectrum
What do different regions do? - ✔✔Radio → microwave → IR → visible → UV → X-ray
→ gamma.
- Cause different transitions (electronic, vibrational, rotational)
increasing freq as well when increasing energy
✔✔types of scattering of radiation - ✔✔Can be used to determine the size of particles
• Rayleigh scattering: greater scattering of
shorter wavelengths
• Scattering by large molecules is different indifferent direction; called Mie scattering
✔✔Polarization of light - ✔✔Restricting the vibration of the light wave to a single plan
✔✔What does quantized energy mean? - ✔✔bound systems (atoms/molecules) have
discrete, quantized energy levels, meaning they can only exist in specific states rather
than a continuous range of energies.
Energy exists in specific levels (not continuous)
✔✔Fluorescence vs Phosphorescence - ✔✔- fluorescence: Fast emission (very quick).
- phosphorescence: Slower emission (lasts longer).
, ✔✔Components of Optical Instruments: Radiation Sources - ✔✔continuous sources:
Emit a wide range of wavelengths. (e.g., Tungsten lamp (visible, 320-2400 nm),
Deuterium lamp (UV, 190-380 nm), Xenon arc lamp (broad, 200-1000 nm)
line sources: Emit specific wavelengths.
(e.g., hollow cathode lamps, electrodeless discharge lamps, lasers).
✔✔Components of Optical Instruments:Wavelength Selectors
components of them are? - ✔✔Allow certain wavelengths through.
- filters: Absorption filters, Interference filters
- monochromator (Device that isolates one wavelength, can be by Prism or Grating
components;
~resolution: Ability to separate close wavelengths.
~bandwidth: Range of wavelengths passed.
~dispersion: Separation of light into wavelengths.
✔✔Components of Optical Instruments: Radiation detectors - ✔✔Photomultiplier Tubes
(PMT): Very sensitive detectors for low light (amplifies signal).
Photodiodes: Convert light into current.
CCD (Charge-Coupled Device): Detects many wavelengths at once (like a camera
sensor).
IR Detectors:
- thermocouples/bolometers: Detect heat (infrared radiation).
✔✔Beer's law and limitations - ✔✔A=εbc
*Absorbance is proportional to concentration*
3 main limitations:
- fundamental limitation: At high concentration, molecules interact → changes
absorptivity.
- chemical limitation: If analyte is in equilibrium, concentration is not accurate.
- instrumental deviation: Stray light and non-monochromatic light.
✔✔Stray Radiation and Non-Monochromatic Radiation - ✔✔Stray Radiation: Extra
unwanted light reaching detector. Makes absorbance LOWER than expected (negative
deviation).
🔹 Non-Monochromatic Radiation:
Beer's Law assumption is that Light is one wavelength (monochromatic), if it's not
Absorbance decreases.
to fix, Measure at λmax (max absorbance).
✔✔Absorption vs interference filter - ✔✔Absorption: wider range
interference: (narrower, more precise)
✔✔Instrument Types for UV/Vis : readout - ✔✔Filter Photometer
Single-Beam Spectrophotometer ⭐
