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Questions and Answers
What process does square wave voltammetry utilize to achieve increased sensitivity?
What process does square wave voltammetry utilize to achieve increased sensitivity?
In stripping voltammetry, what is the main reason for its increased sensitivity?
In stripping voltammetry, what is the main reason for its increased sensitivity?
What measurement is recorded as a function of time in stripping voltammetry?
What measurement is recorded as a function of time in stripping voltammetry?
What characteristic of pulse voltammetry leads to a higher current response?
What characteristic of pulse voltammetry leads to a higher current response?
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What does the current in an electrochemical process indicate?
What does the current in an electrochemical process indicate?
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Which ionization method is characterized by high fragmentation due to the excitement of molecules from electron bombardment?
Which ionization method is characterized by high fragmentation due to the excitement of molecules from electron bombardment?
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What is a primary advantage of using electrospray ionization?
What is a primary advantage of using electrospray ionization?
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Which mass spectrometry technique uses magnetic and electrostatic forces to separate ions based on kinetic energy first?
Which mass spectrometry technique uses magnetic and electrostatic forces to separate ions based on kinetic energy first?
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Which surface spectroscopy technique primarily analyzes emitted electrons to determine elemental composition?
Which surface spectroscopy technique primarily analyzes emitted electrons to determine elemental composition?
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What does the term 'partition coefficient' refer to in chromatographic separation?
What does the term 'partition coefficient' refer to in chromatographic separation?
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In gas chromatography (GC), what is the main function of the carrier gas?
In gas chromatography (GC), what is the main function of the carrier gas?
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Which type of chromatography utilizes both a liquid stationary phase and a gaseous mobile phase?
Which type of chromatography utilizes both a liquid stationary phase and a gaseous mobile phase?
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What is the purpose of the electrostatic field in the X-ray photoelectron spectroscopy instrument?
What is the purpose of the electrostatic field in the X-ray photoelectron spectroscopy instrument?
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What is the main role of the indicator electrode in potentiometry?
What is the main role of the indicator electrode in potentiometry?
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What additional voltage is required in electrolysis to overcome activation energy called?
What additional voltage is required in electrolysis to overcome activation energy called?
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What is the characteristic of a mass spectrometer that provides the highest resolution?
What is the characteristic of a mass spectrometer that provides the highest resolution?
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Which method measures the number of moles of electrons that participate in a chemical reaction?
Which method measures the number of moles of electrons that participate in a chemical reaction?
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Which chromatography method is known for having the capability for both qualitative and quantitative analysis based on peak area?
Which chromatography method is known for having the capability for both qualitative and quantitative analysis based on peak area?
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Which electroanalytical method mainly involves measuring current in response to an applied potential and can reflect concentration changes?
Which electroanalytical method mainly involves measuring current in response to an applied potential and can reflect concentration changes?
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In stripping voltammetry, what is the relationship between peak current during oxidation and analyte concentration?
In stripping voltammetry, what is the relationship between peak current during oxidation and analyte concentration?
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In liquid chromatography, what effect does greater longitudinal diffusion have on peak shape?
In liquid chromatography, what effect does greater longitudinal diffusion have on peak shape?
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What characteristic does supercritical fluid chromatography (SFC) have compared to traditional liquid chromatography (LC)?
What characteristic does supercritical fluid chromatography (SFC) have compared to traditional liquid chromatography (LC)?
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In mass spectrometry, what does the term m/z refer to?
In mass spectrometry, what does the term m/z refer to?
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What process occurs when the silica of the capillary wall binds hydroxide ions (OH)?
What process occurs when the silica of the capillary wall binds hydroxide ions (OH)?
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What achieves separation of ions in capillary electrophoresis based on their charge and size?
What achieves separation of ions in capillary electrophoresis based on their charge and size?
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Which method uses a continuous pH gradient for analyzing analyte ions?
Which method uses a continuous pH gradient for analyzing analyte ions?
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What is the effect of higher pressure programming on supercritical fluid chromatography (SFC)?
What is the effect of higher pressure programming on supercritical fluid chromatography (SFC)?
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What type of detection can be used in supercritical fluid chromatography (SFC)?
What type of detection can be used in supercritical fluid chromatography (SFC)?
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In electron migration during electroosmotic flow, what type of charge is the net flow directed towards?
In electron migration during electroosmotic flow, what type of charge is the net flow directed towards?
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What phenomenon prevents the concentration of electroactive species near an electrode from equalizing with the bulk solution concentration?
What phenomenon prevents the concentration of electroactive species near an electrode from equalizing with the bulk solution concentration?
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What happens in controlled-potential electrolysis?
What happens in controlled-potential electrolysis?
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What is a primary distinguishing feature of polarography?
What is a primary distinguishing feature of polarography?
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Study Notes
Instrumental Review
-
Ion sources:
- Gas-phase source vaporizes and ionizes samples.
- Desorption source converts samples to gaseous ions.
- Electron impact ionization: hard ionization, high fragmentation, sample heated to vapor, bombarded with electrons, molecules excited and fragment.
- Chemical ionization: soft ionization, low fragmentation, molecules ionized by collision with reagent gas ions.
- Electrospray ionization: used for large molecules like proteins, creates charged spray of droplets, solvent evaporates.
- Matrix-assisted desorption ionization: used for biopolymers, analyte in solution under vacuum, laser excites matrix, desorbs and ionizes both analyte and matrix.
Mass Analyzers
- Magnetic sector analyzer: ions accelerated, travel in circular path based on mass-to-charge ratio, scanned at exit slit.
- Double focusing mass spectrometer: uses electrostatic and magnetic analyzers to select ions with specific kinetic energy.
- Time-of-flight (TOF) mass spectrometer: ions accelerated, time to reach detector measured, separates based on mass-to-charge ratio.
- lon trap: ions confined by electric and magnetic fields, sequentially ejected by increasing voltage.
- Orbitrap: ions travel in circular motion around electrode proportional to m/z, current generated and detected.
-
Tandem mass spectrometry: uses multiple mass analyzers for sequential fragmentation of ions.
- Triple quadrupole, QQQ: 1st quadrupole, collision cell, 2nd quadrupole
- QTOF: similar to QQQ but last Q replaced by TOF.
Surface Spectroscopy
- Surface spectroscopy uses beams to probe surface composition
- Techniques: ion beam, electron beam, X-ray, photon beam.
- Ion beam is damaging
- Electron beam penetrates 2-5nm, can determine depth profiles with sputtering
- X-ray and UV beam used in X-ray photoelectron spectroscopy to determine elemental composition.
- Photon beam is less damaging, used in Surface Plasmon Resonance for surface interaction analysis.
Chromatography
- Chromatographic separation: Mobile phase forces solutes through the stationary phase.
- Elution: Solutes are washed through the column.
- Partition coefficient: ratio of concentration between two solvents.
- Column performance: Improved column performance through better separation or reducing band broadening.
- Dead time: Time taken for non-retained species to reach the detector.
- Column bleeding: small amounts of stationary phase are carried out of the column during elution.
- Theoretical plates: layers of packing material, column efficiency measured by plate count (N).
- Higher efficiency = smaller plate height (H).
Electrochemistry
- Voltammetry: method measures current as a function of applied potential.
- Voltammogram: Plot of current versus potential.
- Cyclic voltammetry: Triangle waveform, measures both anodic and cathodic processes. Peak heights proportional to concentration.
- Electrolysis: Process that forces a chemical reaction to occur on electrode using voltage.
- Overpotential: voltage required to activate an electrode reaction.
-
Ohmic potential (IR drop): a voltage needed to overcome internal resistance of electrochemical cell.
- Concentration polarization: Concentration of electroactive species at or near the electrode surface differs from the bulk concentrations, opposing electrolysis.
Other Techniques
- Coulometry: Measures the number of electrons consumed in a reaction to determine concentration.
- Amperometry: Measures current at a fixed potential for analyte concentration.
- Polarography: Measures current flowing through a dropping mercury electrode as a function of applied potential.
- Capillary Electrophoresis: Separation method based on charge and size ratio of ions in electric field.
- High Performance Liquid Chromatography (HPLC) - useful to analyze mixtures with higher resolution and different polarity or strengths.
- Supercritical Fluid Chromatography (SFC) - suitable to separate larger molecules, higher diffusion rates, sharper peaks compared to HPLC.
- Gas Chromatography (GC) - useful to analyze volatile components because they exist as gases.
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Description
This quiz covers the fundamentals of ion sources and mass analyzers used in mass spectrometry. Learn about various ionization methods such as electron impact and electrospray ionization, as well as different types of mass analyzers like magnetic sector analyzers. Test your knowledge and understanding of these critical concepts in analytical chemistry.
