Spectroscopy Basics
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Questions and Answers

What is spectroscopy?

The study of the interaction between electromagnetic radiation and matter.

What is electromagnetic radiation?

The type of energy that is transmitted through space at enormous velocities.

What does Amplitude (A) refer to in the context of waves?

The length of the electrical vector at the maximum in the wave.

What is wavelength (λ)?

<p>The linear distance between successive maxima or minima of a wave.</p> Signup and view all the answers

What is frequency (n)?

<p>The number of oscillations of the field per second.</p> Signup and view all the answers

What are photons or quanta?

<p>Packets of energy that electromagnetic radiation is made up of.</p> Signup and view all the answers

What is a chromophore?

<p>A functional group that absorbs light such as C=C, C=O, N=N, and N=O, having multiple bonding.</p> Signup and view all the answers

What are auxochromes?

<p>Functional groups that do not absorb in the UV/VIS region.</p> Signup and view all the answers

What is stray light?

<p>Unwanted light of wavelengths that differ from the target wavelength.</p> Signup and view all the answers

What is a disadvantage of a Single-Beam Spectrophotometer?

<p>Influenced by instability of light source.</p> Signup and view all the answers

What is an advantage of a Double-Beam Spectrophotometer?

<p>Not influenced by instability of light source.</p> Signup and view all the answers

What is a D2 lamp used for?

<p>Measurement in the ultraviolet region (190 to 350 nm).</p> Signup and view all the answers

What is a Halogen lamp used for?

<p>Measurement in the visible region (350 to 900 nm).</p> Signup and view all the answers

What region of the spectrum does a Deuterium/ Hydrogen Discharge Lamp provide a continuous source?

<p>Ultraviolet region.</p> Signup and view all the answers

A spectrophotometer generally has an entrance _____ and an exit _____.

<p>slit</p> Signup and view all the answers

What happens if the slit width is increased in a spectrophotometer?

<p>The intensity of the light irradiating the sample increases but the resolution worsens.</p> Signup and view all the answers

Give an example of a cuvette and its range.

<p>Quartz/fused silica cuvette - Wide range from 190 to 2500nm; Stable with most acids, bases, and organic solvents</p> Signup and view all the answers

What is the useful region for a Silicate glass cuvette?

<p>350 - 2000 nm; Windows of good quality optical glass transmit well throughout the visible range</p> Signup and view all the answers

Describe Plastic cuvettes.

<p>Disposable cells are molded from polystyrene methacrylate and other transparent plastics.</p> Signup and view all the answers

What is a photodiode?

<p>A type of semiconductor element that is used to convert light energy into electrical energy. It uses an electrical phenomenon called the 'photovoltaic effect' whereby a reverse current proportional in size to the light intensity is created.</p> Signup and view all the answers

What is UV/Vis spectroscopy suitable for?

<p>Characterization, but not for structural elucidation.</p> Signup and view all the answers

What role has UV/Vis spectroscopy taken?

<p>UV/Vis spectroscopy has taken a more important role in quantitation, rather than structural determination.</p> Signup and view all the answers

How would you measure a transparent liquid?

<p>Transmittance method.</p> Signup and view all the answers

How would you measure an opaque liquid?

<p>Reflectance method (by integrating sphere).</p> Signup and view all the answers

How would you measure solid powder/coatings/mirrored surfaces liquids?

<p>Reflectance method (by integrating sphere or specular reflectance accessories).</p> Signup and view all the answers

Describe single point calibration.

<p>Only 1 calibration standard is prepared; Mainly applied to pass/ fail situation; No way to identify dilution error from the graph</p> Signup and view all the answers

Describe multipoint calibration.

<p>At least 2 calibration standards are needed; More accurate method; Easier to identify dilution error occur in one of the standards</p> Signup and view all the answers

How many serial dilutions should you perform?

<p>Perform serial dilution to obtain generally 3 to 5 calibration standards.</p> Signup and view all the answers

What range should the concentration of standards fall between?

<p>Concentration of standards should fall between 0 to 0.4 absorption unit (depends on unit specs).</p> Signup and view all the answers

What is derivative spectroscopy?

<p>The derivatives of an absorbance with respect to the wavelength.</p> Signup and view all the answers

What are Integrating Spheres (ISR) used for?

<p>Used for measurement of diffuse and total reflectance, diffuse and total transmittance.</p> Signup and view all the answers

What is chromatography?

<p>Method for separating the solute from the stationary or mobile phase based on the difference in interaction</p> Signup and view all the answers

In what year was the birth of high performance liquid chromatography?

<p>1969</p> Signup and view all the answers

What is Polarity?

<p>Localization of electrons within a molecule can cause molecules to have negative and/or positive poles.</p> Signup and view all the answers

What is stationary phase in Normal-Phase/Absorption Chromatography?

<p>High polarity</p> Signup and view all the answers

What is mobile phase in Normal-Phase/Absorption Chromatography?

<p>Low Polarity</p> Signup and view all the answers

What is stationary phase in Reversed-Phase Chromatography?

<p>Low polarity</p> Signup and view all the answers

What is mobile phase in Reversed-Phase Chromatography?

<p>High polarity</p> Signup and view all the answers

What is Size Exclusion Chromatography?

<p>Chromatography method that separates compounds by molecular size (bulkiness).</p> Signup and view all the answers

Flashcards

Spectroscopy

The study of the interaction between electromagnetic radiation and matter.

Electromagnetic radiation

The type of energy that is transmitted through space at enormous velocities.

Amplitude (A)

The length of the electrical vector at the maximum in the wave.

Wavelength (λ)

The linear distance between successive maxima or minima of a wave.

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Frequency (n)

The number of oscillations of the field per second.

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Photons/Quanta

Packets of energy that make up electromagnetic radiation.

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Chromophore

Functional group that absorbs light like C=C or C=O.

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Auxochromes

Functional group that does not absorb in the UV/VIS region.

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Stray light

Unwanted light of wavelengths differing from the target wavelength.

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Single-Beam Spectrophotometer

Influenced by instability of light source.

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Double-Beam Spectrophotometer

Not influenced by instability of light source.

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D2 lamp

Used for measurement in the ultraviolet region (190 to 350 nm).

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Halogen lamp

Used for measurement in the visible region (350 to 900 nm).

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Quartz/fused silica cuvette

Stable cuvette from 190 to 2500nm; resistant to most chemicals.

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Plastic cuvette

Disposable cells made from transparent plastics.

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Photodiode

Converts light energy into electrical energy using the photovoltaic effect.

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Single point calibration

Only 1 calibration standard is prepared.

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Multipoint calibration

At least 2 calibration standards are needed for accuracy.

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Size Exclusion Chromatography

Method that separates compounds by molecular size.

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Polarity

Localization of electrons creates negative and/or positive poles in molecules.

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High polarity

Stationary phase in Normal-Phase Chromatography.

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Low polarity

Mobile phase in Reversed-Phase Chromatography.

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Derivative spectroscopy

The derivatives of absorbance with respect to wavelength.

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Study Notes

Spectroscopy

  • Spectroscopy studies the interaction of electromagnetic radiation with matter.
  • Electromagnetic radiation travels at enormous velocities.

Electromagnetic Radiation Properties

  • Amplitude (A): The maximum length of the electrical vector in a wave.
  • Wavelength (λ): The distance between successive wave maxima or minima.
  • Frequency (ν): The number of oscillations per second.
  • Photons/Quanta: Packets of energy that make up electromagnetic radiation.

Chromophores and Auxochromes

  • Chromophores: Functional groups that absorb light (e.g., C=C, C=O, N=N, N=O).
  • Auxochromes: Functional groups that don't absorb in the UV/Vis region.

Spectrophotometer Types

  • Single-Beam: Affected by light source instability.
  • Double-Beam: Unaffected by light source instability.

Light Sources

  • D2 lamp: Used for UV measurements (190-350 nm).
  • Halogen lamp: Used for visible measurements (350-900 nm).
  • Deuterium/Hydrogen Discharge lamp: Continuous UV source.

Spectrophotometer Components and Settings

  • Slit: Entrance and exit slits in spectrophotometers.
  • Slit width: Increased width yields higher light intensity but lower resolution; decreased width offers lower intensity but higher resolution.
  • Cuvettes: Quartz/fused silica (190-2500 nm, stable with many substances), silicate glass (350-2000 nm), plastic (disposable).
  • Photodiode: Converts light energy to electrical energy (photovoltaic effect).

UV/Vis Spectroscopy

  • UV/Vis Spectroscopy is useful for quantitation, not structural elucidation.

Sample Types and Measurement Methods

  • Transparent liquids: Measured by transmittance.
  • Translucent liquids: Measured by transmittance or reflectance (integrating sphere).
  • Opaque liquids: Measured by reflectance (integrating sphere).
  • Solids (powders, coatings): Measured by reflectance (integrating sphere or specular reflectance accessories).

Calibration Methods

  • Single-point calibration: Uses only one standard, simple but less accurate for quantitative analysis.
  • Multipoint calibration: Uses multiple standards (3-5), more accurate, helps identify dilution errors.

Calibration Procedures

  • Perform serial dilutions for calibration standards (3-5).
  • Scan standards to determine maximum absorption peak wavelength (0-0.4 absorbance units, depends on instrument).

Advanced Spectroscopy Techniques

  • Derivative spectroscopy: Calculates absorbance derivatives wrt wavelength.
  • Integrating Spheres (ISR): Measures diffuse and total reflectance/transmittance.

Chromatography

  • Chromatography separates solutes based on differences in interaction with stationary and mobile phases.

HPLC (High Performance Liquid Chromatography)

  • Introduced in 1969.

Chromatography Phases

  • Normal-phase chromatography: High polarity stationary phase, low polarity mobile phase.
  • Reversed-phase chromatography: Low polarity stationary phase, high polarity mobile phase.
  • Size Exclusion Chromatography: Separates compounds based on molecular size.

Chromatography Polarity

  • Polarity in molecules relates to negative and positive poles caused by electron localization.

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Explore the principles of spectroscopy, including electromagnetic radiation properties like amplitude, wavelength, and frequency. Learn about chromophores, auxochromes, and the different types of spectrophotometers. Discover light sources such as D2 and Halogen lamps used in UV and visible measurements.

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