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Questions and Answers
What is the primary function of chromophores in substances?
What is the primary function of chromophores in substances?
Which wavelengths of light do chromophores typically absorb?
Which wavelengths of light do chromophores typically absorb?
Which components make up the term 'chromophore'?
Which components make up the term 'chromophore'?
What would be the likely consequence of a substance lacking chromophores?
What would be the likely consequence of a substance lacking chromophores?
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Which of the following characteristics does NOT define a chromophore?
Which of the following characteristics does NOT define a chromophore?
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What happens to a sample as it absorbs electromagnetic radiation?
What happens to a sample as it absorbs electromagnetic radiation?
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Which statement accurately describes photons?
Which statement accurately describes photons?
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If electromagnetic radiation is classified only as photons, what can be inferred about its properties?
If electromagnetic radiation is classified only as photons, what can be inferred about its properties?
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What is the primary result of energy change in a sample due to electromagnetic radiation absorption?
What is the primary result of energy change in a sample due to electromagnetic radiation absorption?
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Electromagnetic radiation is known to consist of what?
Electromagnetic radiation is known to consist of what?
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What effect does the addition of NH3 in an acidic medium have on light absorption?
What effect does the addition of NH3 in an acidic medium have on light absorption?
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How does the polarity of solvents influence absorption spectra?
How does the polarity of solvents influence absorption spectra?
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Which of the following statements about solvent effects on absorption spectra is accurate?
Which of the following statements about solvent effects on absorption spectra is accurate?
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If the solvent is less polar, what is the likely effect on the absorption spectrum?
If the solvent is less polar, what is the likely effect on the absorption spectrum?
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In the context of NH3 in acidic conditions, what is the observed outcome on absorption properties?
In the context of NH3 in acidic conditions, what is the observed outcome on absorption properties?
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What does a bathochromic shift indicate about a substance's absorption spectrum?
What does a bathochromic shift indicate about a substance's absorption spectrum?
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Which phenomenon involves energy transfer and subsequent light emission due to molecular interactions?
Which phenomenon involves energy transfer and subsequent light emission due to molecular interactions?
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In the context of conjugated systems, which factor is least likely to cause a bathochromic shift?
In the context of conjugated systems, which factor is least likely to cause a bathochromic shift?
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What is the primary cause of bathochromic shifts in absorption spectra?
What is the primary cause of bathochromic shifts in absorption spectra?
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Which statement about spectral changes is the most accurate?
Which statement about spectral changes is the most accurate?
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What is the relationship between a molecule's absorption of ultraviolet radiation and its fluorescence intensity?
What is the relationship between a molecule's absorption of ultraviolet radiation and its fluorescence intensity?
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Which of the following types of compounds are likely to exhibit fluorescence?
Which of the following types of compounds are likely to exhibit fluorescence?
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Under what conditions would a molecule most likely demonstrate fluorescence?
Under what conditions would a molecule most likely demonstrate fluorescence?
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Which statement is true regarding the fluorescence properties of molecules?
Which statement is true regarding the fluorescence properties of molecules?
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What factor primarily influences the intensity of fluorescence in a molecule?
What factor primarily influences the intensity of fluorescence in a molecule?
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What potential impact can impurities during drug discovery have on health sciences?
What potential impact can impurities during drug discovery have on health sciences?
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How has the analysis of drug molecules impacted health sciences research?
How has the analysis of drug molecules impacted health sciences research?
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What does the introduction of impurities imply for the drug development process?
What does the introduction of impurities imply for the drug development process?
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Which of the following statements about impurities in drug development is true?
Which of the following statements about impurities in drug development is true?
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What is one of the consequences of impurities in drug discovery?
What is one of the consequences of impurities in drug discovery?
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What is the effect of a bathochromic shift on the absorption spectrum?
What is the effect of a bathochromic shift on the absorption spectrum?
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Which of the following factors is primarily responsible for a bathochromic shift?
Which of the following factors is primarily responsible for a bathochromic shift?
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What does the term 'bathochromic' specifically refer to in terms of wavelength changes?
What does the term 'bathochromic' specifically refer to in terms of wavelength changes?
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In the context of spectral changes, what is the influence of solvent effects on absorption?
In the context of spectral changes, what is the influence of solvent effects on absorption?
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Which of the following statements about fluorescence and phosphorescence is true?
Which of the following statements about fluorescence and phosphorescence is true?
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Study Notes
Pharmaceutical Analytical Chemistry III (PA 303)
- Level 2 PharmD (Spectroscopy)
- Lecture 1, Dr. Bassam Shaaban (10/10/2023)
Contents
- Principles of spectrophotometry
- Light and radiation
- Electromagnetic spectrum
- Light as energy
- Interaction of photons with matter
- Absorption spectrum, characteristics and shifts
- Types of electronic transitions
- Chromophores and auxochromes
- Factors affecting absorption spectrum (pH, solvent)
- Quantitative spectrophotometry (laws of light absorption)
- Instrumentation (basic component of spectrophotometer)
- Applications of spectrophotometry
Analytical Chemistry
- Volumetric analysis (indirect method)
- Qualitative analysis
- Quantitative analysis
- Volumetric analysis
- Instrumental analysis (Spectroscopy, Electrochemical, Chromatography)
Instrumental Methods of Analysis (Physicochemical)
- Measuring physical properties quantitatively related to constituent concentration.
- Requires specific instruments for instrumental analysis.
- Uses a stimulus (light, heat, current, or voltage) applied to sample.
- Signal is processed, and analyzed, to give a readout (meter, plotter, or computer).
Spectroscopy
- Why do solutions/matter appear colored?
- Light (electromagnetic radiation) composed of electric and magnetic components.
- EMR is made up of discrete packets of energy called photons or quanta.
- EMR also has wave-like properties described by wave motion.
Wave Properties of Electromagnetic Radiation
- Light exhibits both wave and particle properties.
- Light waves travel at the highest known speed of 3 x 10⁸ m/s.
- Wavelength classification according to the wavelength (λ).
Wavelength
- Linear distance between the crests of two successive waves.
Units of Length
- 1 angstrom (A°) = 10⁻¹⁰ m = 10⁻⁸ cm
- 1 nanometer (nm) = 10 A° = 10⁻⁷ cm
- 1 micrometer (µm) = 10⁴ A° = 10⁻⁴ cm
Wavelength and Frequency
- Frequency (ν) and wavelength (λ) are inversely proportional. (λ=c/ν)
- where c is the speed of light
Particle Properties of Electromagnetic Radiation
- Electromagnetic radiation consists of photons
- Photon energy is directly proportional to the frequency (E=hν)
- where h is Planck's constant (6.63 x 10⁻³⁴J.s)
Electromagnetic Spectrum
- Ranges from very short to very long wavelengths.
- Includes gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves.
- Each region has a unique range of wavelengths and frequencies.
UV-Visible Spectrum
- Region of the electromagnetic spectrum the human eye can perceive. (400 - 780 nm).
- Spectroscopic technique useful to identify and measure concentrations of solutions.
Color
- White light is passed through a prism, broken into a spectrum of colors (red, orange, yellow, green, blue, indigo, violet).
Color Wheel
- Visual tool for illustrating color relationships.
- Primary colors: red, yellow, blue
- Complementary colors: colors opposite each other on the color wheel
Interactions of Photons with Matter
- Three basic processes by which a molecule (or atoms) absorbs radiation:
- Rotational transitions
- Vibrational transitions
- Electronic transitions
Electronic Spectrum
- Molecules at room temperature are generally in their lowest electronic energy state (ground state)
- Upon interaction with UV or visible photons, an outer electron (valence electron) in the molecule can move to a higher electronic energy level (excited state).
- Energy change associated follows the equation: ΔE=Es-Eg=hv = hc/入.
Lecture 2, Dr. Bassam Shaaban, PhD (12-Oct-24)
UV-Vis Luminescence Spectroscopy
-
Human eye can perceive narrow electromagnetic spectrum. ~400-800nm
-
UV-visible absorption spectra can identify compounds and quantify concentrations of solutions.
Electron Interactions
Molecules are typically in their ground state. Excited molecules can relax through several pathways;
- Non-radiative processes:
- Heat release
- Chemical Reaction
- Internal conversion / External Conversion
- Radiative process: Emission of photons
- Fluorescence (fast)
- Phosphorescence (slow).
UV-Vis Transitions
- σ electrons usually require high-energy photons, Absorption occurs in the far UV region
- π electrons are involved in absorption but need less energy, commonly the medium to high UV range.
- n electrons is weaker than the others, Absorption occurs in UV region.
Types of Electrons
-
Closed shell electrons: not involved in bonding
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Covalent single bond electrons: high excitation energy, thus require UV energy
-
Electrons in π orbital (double or triple bonds): medium range of energy.
-
Paired non-bonding outer electrons (n electrons): low excitation energy.
Types of Electronic Transitions
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σ → σ (saturated compounds, require high energy photons)
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π → π (conjugated compounds, medium energy photons)
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n→π n electrons relax faster, low excitation energy.
Absorption Spectra
-
Characterization spectra; plot of absorbance versus wavelength.
- Shows the wavelength of maximum absorption(λmax)
-
Line spectra: atomic spectra, sharp, single wavelength of absorbance (e.g., sodium).
-
Band spectra: molecular spectra, combinations of vibration and rotation sub levels with maxium absorption(λmax)
Factors Affecting Absorption Spectra
-
pH: spectra of compounds with acidic or basic groups is dependent on pH.
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Solvents: less polar solvents interact less strongly with solute than polar solvents, influence positioning of max.
Types of Spectrophotometers
- Single-beam spectrophotometers
- Double-beam spectrophotometers; more accurate, sample measured twice by the same components simultaneously by use of beam spitter
Components of Spectrophotometers
-
Light source (Xenon and Mercury lamps depending on UV or Visible spectra)
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Monochromator (Filters or grating to select certain wavelengths)
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Sample cell (Transparent to wavelength of light of interested region, glass or Quartz cuvettes)
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Detector (measures intensity of emitted light, phototubes and photomultiplier tubes)
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Recorder (analog or digital recording of signal on paper or computer)
Applications
-
Qualitative analysis (identification of compounds): based on unique spectra.
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Quantitative analysis (measuring the concentration of compounds): Beer-Lambert law (amount of absorption of solution is directly proportional to concentration)
Deviations from Beer-Lambert's Law
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Deviation from Beer-Lambert's Law is due to interactions and association between analyte molecules at high concentrations.
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Instrumental errors: Unmatched cells, unclean handling or optics can distort absorbance at high concentration, and stray light from non sample sources.
Spectrophotometric Titration
- Measuring absorbance during titration to determine the end-point.
Advantages of Spectrophotometry
- Applicability: many organic/inorganic compounds absorb light
- High sensitivity: to accurately measure concentrations of the micro molar range
- Selectivity: due to selective reactions, measurements, and mathematical treatment
- Accuracy / Precision: has good accuracy, relative errors of 0.1 - 2%
- Convenient : rapid and useful method
Disadvantages of Spectrophotometry
- Interference from other substances (only if end point depends on the absorbance).
Additional Notes
- Factors that can affect the absorption of light (spectra) ; pH Solvent Concentration
- Additional study information on the spectral characteristic of each analyte(substance).
Lecture 3, 10/19/2024
Contents
- Principles of spectrophotometry
- Light and radiation
- Electromagnetic spectrum
- Light as energy
- Interaction of photons with matter
- Absorption spectrum, characteristics, and shifts
- Types of electronic transitions
- Chromophores and auxochromes
- Quantitative spectrophotometry (laws of light absorption)
- Factors affecting absorption spectrum (pH, solvent)
- Instrumentation (basic components of spectrophotometer)
- Applications of spectrophotometry
Factor Affecting on Absorption Spectra
- pH
- Solvents
Lecture 4, 10/27/2024
Contents
- Principles of spectrophotometry
- Light and radiation
- Electromagnetic spectrum
- Light as energy
- Interaction of photons with matter
- Absorption spectrum, characteristics, and shifts
- Types of electronic transitions
- Chromophores and auxochromes
- Quantitative spectrophotometry (laws of light absorption)
- Factors affecting absorption spectrum (pH, solvent)
- Instrumentation (basic component of spectrophotometer)
- Applications of spectrophotometry
Additional Notes
- Principles of atomic and molecular spectroscopy
Fluorimetry Lecture
-
Introduction to the basics of fluorimetry
- Principles of photoluminescence
-
Variables that affect fluorescence intensity
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Advantages / Disadvantages of Fluorimetry
-
Instrumentation (components of a fluorimeter, including filters, light sources, and detectors)
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Practical aspects of multi-component analysis
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Understanding how to select the ideal derivative order for given measurements
Multicomponent Analysis
- Multicomponent analysis methodology
- Analysis of binary mixture (via simultaneous equations or derivative spectroscopy)
Atomic Spectroscopy
- Principles of Atomic Absorption Spectroscopy (AAS) and Flame Emission Spectroscopy (FES)
- Characteristics and methods of determination
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Description
This quiz explores the role of chromophores in substances, including their function, the wavelengths of light they absorb, and the effects of solvents on absorption spectra. Understand the implications of chromophore presence or absence and the fundamental properties of electromagnetic radiation. Test your knowledge on these essential concepts in chemistry.
