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Questions and Answers
What is a key feature of the Soft ionization technique used in ESI?
What is a key feature of the Soft ionization technique used in ESI?
What is one major advantage of using MALDI for mass spectrometry?
What is one major advantage of using MALDI for mass spectrometry?
Which application is specifically suited for ESI?
Which application is specifically suited for ESI?
What is a disadvantage of using MALDI in mass spectrometry?
What is a disadvantage of using MALDI in mass spectrometry?
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What pre-treatment is necessary before using ESI mass spectrometry?
What pre-treatment is necessary before using ESI mass spectrometry?
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What is the primary purpose of mass spectrometry?
What is the primary purpose of mass spectrometry?
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What kind of analysis is mass spectrometry less effective for when dealing with unknown compounds?
What kind of analysis is mass spectrometry less effective for when dealing with unknown compounds?
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What is formed when organic molecules are bombarded with a beam of electrons in mass spectrometry?
What is formed when organic molecules are bombarded with a beam of electrons in mass spectrometry?
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What type of ions are detected in mass spectrometry?
What type of ions are detected in mass spectrometry?
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What does the mass spectrum output indicate?
What does the mass spectrum output indicate?
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Which measurement does mass spectrometry NOT typically provide?
Which measurement does mass spectrometry NOT typically provide?
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During mass spectrometry, how are ions sorted?
During mass spectrometry, how are ions sorted?
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In mass spectrometry, which type of ions can further break up into smaller ions?
In mass spectrometry, which type of ions can further break up into smaller ions?
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What is the intensity of the base peak in a mass spectrum?
What is the intensity of the base peak in a mass spectrum?
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Which component of a mass spectrometer is responsible for ionizing the sample?
Which component of a mass spectrometer is responsible for ionizing the sample?
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At what energy level do molecular ions typically form during ionization?
At what energy level do molecular ions typically form during ionization?
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What is a key advantage of the Electrospray Ionization technique?
What is a key advantage of the Electrospray Ionization technique?
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What does the final peak (M+) in a mass spectrum represent?
What does the final peak (M+) in a mass spectrum represent?
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Which of the following is a disadvantage of Electrospray Ionization?
Which of the following is a disadvantage of Electrospray Ionization?
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Which component of the mass spectrometer accelerates ions into the mass analyzer?
Which component of the mass spectrometer accelerates ions into the mass analyzer?
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What does the position of the tallest peaks in a mass spectrum indicate?
What does the position of the tallest peaks in a mass spectrum indicate?
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Study Notes
Introduction to Mass Spectrometry
- Mass spectrometry is a powerful analytical technique used to identify unknown compounds, determine structure and chemical properties in a sample.
- It requires only a few nanomoles of sample.
- It provides characteristic information such as structure and molecular weight.
- Modern mass spectrometry is used in various fields including pharmaceutical, clinical, geological, biotechnology, and environmental studies.
Main Information in MS Analysis
- Molecular weight: Determined based on isotope peaks.
- Number of specific elements: Also determined from isotope peaks.
- Molecular formula: Obtained using high-resolution mass spectrometry.
- Reproducible fragment patterns: Analyzed to identify functional groups and confirm compound identity.
Principles of Mass Spectrometry
- Sample molecules are ionized in the gas phase.
- Ions are separated based on their mass-to-charge ratio.
- The separated ions are detected, and a mass spectrum is generated.
- The mass spectrum is a plot of ion abundance versus mass-to-charge ratio.
- Organic molecules in gaseous state are bombarded by high energy electrons (typically 70 eV).
- Molecular or parent ions break down into smaller ions (fragment ions or daughter ions).
- The ions are accelerated by an electric field.
- Ions are separated by deflection in a magnetic field based on their mass-to-charge ratio.
- The output is the mass spectrum where each line represents an atom or molecule of a particular mass.
The most intense peak is the base peak, assigned a value of 100. Other peaks are compared to it in terms of intensity.
Mass Spectrometer Components
- Sample inlet: Introduces sample into the instrument.
- Ionization source: Ionizes the sample molecules. Common processes include Electron Ionization (EI), Chemical Ionization (CI), Fast Atom Bombardment (FAB), Electrospray Ionization (ESI), and Matrix-Assisted Laser Desorption/Ionization (MALDI).
- Mass analyzer: Separates the ions based on mass-to-charge ratio. Common analyzers include Quadrupole, Magnetic Sector, and Time-of-Flight (TOF).
- Ion detector: Measures the abundance of ions.
- Vacuum system: Maintains a low-pressure environment in the instrument.
Ion Source
- Ionization of the organic compound is the fundamental step in mass spectral analysis.
- The minimum energy required for sample or organic molecule ionization is termed as ionization potential.
- The ion source is a crucial component that ionizes the material being analyzed.
- Ions are then transported to the mass analyzer.
- Molecular ions are created when the electron beam energy reaches 10-15 eV. Fragmentation of ions occurs at higher bombardment energies, typically 70 eV.
- Primary functions of the ion source are to produce ions (without mass discrimination) and accelerate ions into the mass analyzer.
Electrospray Ionization (ESI)
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ESI is a "soft" ionization technique ideal for large biological molecules (proteins, peptides, macromolecules).
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It provides good sensitivity for accurate quantitative and qualitative measurements.
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ESI handles samples with high masses and analyzes those with non-covalent interactions.
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Advantages: Ability to handle high-mass samples, one of the softest ionization methods, good sensitivity.
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Disadvantages: Cannot analyze mixtures well (unreliable results), often becomes contaminated, multiple charges, prior separation (by chromatography) is necessary.
Matrix-Assisted Laser Desorption Ionization (MALDI)
- MALDI is also a "soft" ionization method, suitable for large molecules and solid samples with low volatility or high mass.
- Advantages: Gentle ionization, works well with high molecular weight analytes, does not require volatility, produces singly charged ions, separation by chromatography is not necessary.
- Disadvantages: Matrix cluster ions can obscure low m/z species (less than 600), analytes that absorb laser light, and limitations in compatibility with some mass analyzers.
Quadrupole Mass Analyzer
- Quadrupole mass analyzers are used in mass spectrometry for their high degrees of accuracy and precision (micrometer-level).
- It involves four precisely aligned rods creating a mass filter by oscillating electric fields.
- Used in fast and precise analysis of gas and vapors.
- Three basic elements: ion source, mass filter, ion detector.
Time-of-Flight (TOF) Mass Analyzer
- TOF analyzers are non-scanning analyzers.
- Analyzers emit pulses of ions from the source with equal kinetic energy before entering a drift region (flight tube).
- Ions travel through a flight tube to a detector, and the time required for each ion to travel reflects its mass.
- Two main types: linear TOF and reflectron TOF.
Tandem Mass Spectrometry (MS/MS)
- MS/MS uses multiple mass analyzers in a single instrument.
- Allows the selection of a specific analyte, generating fragments for structural elucidation.
Classic Mass Spectrometry Benefits & Limitations
- Benefits: Classical mass spectra, good repeatability, relatively small and cost-effective systems.
- Limitations: Limited resolution, peak heights variable as a function of mass discrimination, incompatibility with pulsed ionization methods (CID), mass spectra quality dependent on numerous factors.
Magnetic Sector Mass Analyzer
- Magnetic sector mass analyzers are sophisticated and are considered mature technologies.
- Analyzers often use electric sectors along with magnetic ones to correct for differences in ion velocities and achieve high resolution and sensitivity.
- They provide classical mass spectra, are highly reproducible, and have high resolution and sensitivity.
- <summary>Expensive instruments.</summary>
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Description
Explore the fundamentals of mass spectrometry, a crucial technique for analyzing unknown compounds and determining their structure and properties. Discover how molecular weight, functional groups, and other characteristics are identified using various methods in mass spectrometry. This quiz will test your knowledge on the principles and applications of this analytical technique.
