Name: how mass spectrometers sort ions
Uploaded: 2024-04-04T10:51:33.000Z
Duration: 1 min 16 s
Channel: JoVE

Das Massenspektrometer ionisiert Moleküle und erzeugt aus der Fragmentverteilung ein Massenspektrum.
Es erfüllt drei Funktionen: Ionisierung von Molekülen oder Atomen, Trennung der Ionenfragmente und Nachweis von Ionen.
Bei der Elektronenionisation, einer gängigen Ionisationsmethode, erzeugt eine verdampfte Probe in der Ionisationskammer, die mit einem hochenergetischen Elektronenstrahl beschossen wird, radikalische Kationen. Das Radikalkation zerfällt schnell in neutrale Moleküle, Radikale und Kationen.
Die Kationen werden dann durch eine Reihe von negativ geladenen Beschleunigerplatten in eine Analysekammer beschleunigt.
Viele gängige Analysatoren legen ein magnetisches oder elektrisches Feld an die Analysekammer an, das die Flugbahnen der Ionen basierend auf ihrer Masse und Ladung biegt.
Nur Ionen mit bestimmten m/z-Werten haben die exakte Bahn, um den schmalen Schlitz vor dem Ionendetektor für ein gegebenes magnetisches oder elektrisches Feld zu passieren.
Durch die Veränderung des Feldes scannt der Massenanalysator einen Bereich von Ionenmassen, wobei ihre Häufigkeiten im Massenspektrum aufgezeichnet werden.

massenspektrometer

Mass Spectrometers

In dieser Lektion wird die Instrumentierung eines Massenspektrometers detailliert beschrieben – ein physikalisches Instrument zur Durchführung von Massenspektrometrie an Analytmolekülen und zur Aufzeichnung der charakteristischen Massenspektren. Dies wird durch drei Hauptfunktionen erreicht:

<ol>
	<li>Umwandlung der Atome/Moleküle des Analyten in der Gasphase in einen Strahl positiv oder negativ geladener Ionen durch Ionisierung.</li>
	<li>Trennung der geladenen Spezies anhand ihres Masse-Ladungs-Verhältnisses.</li>
	<li>Aufzeichnung der relativen Häufigkeit der einzelnen Ionenart.</li>
</ol>

In der Ionisationskammer des Massenspektrometers wird der verdampfte Analyt im Vakuum mit hochenergetischen Elektronen beschossen. Die Energie des Elektrons beträgt etwa 70 eV und reicht aus, um dem Analyten ein Elektron zu entziehen. Das resultierende Molekülion fragmentiert weiter in geladene Spezies und neutrale Moleküle. Das Massenspektrometer erfasst nur die Masse der geladenen Spezies, da die Ladung die Steuerung der Moleküle durch ein elektrisches oder magnetisches Feld ermöglicht.

Das Molekülion und seine geladenen Fragmente werden durch eine Reihe von negativ geladenen Beschleunigerplatten beschleunigt, die in der Analysekammer in geeigneter Weise im Detektor angeordnet sind. Auf dem Weg zwischen der Beschleunigerplatte und dem Detektor wird ein Magnetfeld angelegt, das eine Kurve im Weg der geladenen Spezies verursacht. Bei einem konstanten Magnetfeld hängt der Krümmungsradius von der Molekülmasse der geladenen Spezies ab. Durch die Platzierung eines Schlitzes vor dem Detektor wird sichergestellt, dass nur geladene Spezies mit einem bestimmten Molekulargewicht den Detektor erreichen.

Durch Variation des Magnetfelds können die geladenen Spezies aller Molekulargewichte am Detektor aufgezeichnet werden, und zwar jeweils eine einzelne Molekulargewichts-Spezies. Durch das Scannen aller Magnetfelder liefert das Massenspektrometer Informationen über die relative Häufigkeit aller geladenen Spezies als Massenspektrum.

Massenspektrometer

In dieser Lektion wird die Instrumentierung eines Massenspektrometers beschrieben – ein physikalisches Instrument zur Durchführung von Massenspektrometrien an Analytmolekülen und zur Aufzeichnung von ...

Education

Lehre

JoVE Core

Analytical Chemistry

Analytische Chemie

Unit 1

Einheit 1

Principles of Mass Spectrometry

Prinzipien der Massenspektrometrie

KEY TERMS AND CONCEPTS

KERNBEGRIFFE UND KONZEPTE

how mass spectrometers sort ions

A mass spectrometer sorts charged ions by their mass-to-charge ratio and records their relative abundance. It turns vaporized analyte molecules into ions, separates them, and then measures the signal from each type of ion.

The process begins in the ionization chamber. The analyte is in the gas phase inside a vacuum, and it is struck by high-energy electrons. The electrons have about 70 eV of energy, which is enough to remove an electron from the analyte and form a molecular ion.

After ionization, the molecular ion can break into charged fragments and neutral molecules. The instrument records only the charged species. Their charge allows them to be controlled by electric or magnetic fields.

Next, the molecular ion and its charged fragments are accelerated by a set of negatively charged accelerator plates. These plates move the ions toward the detector in the analyzing chamber. A magnetic field bends the path of the ions as they travel between the accelerator plate and the detector.

At a constant magnetic field, the radius of the curved path depends on the molecular mass of the charged species. A slit placed in front of the detector helps admit only ions with a particular molecular weight. By changing the magnetic field, ions of different molecular weights can reach the detector one at a time.

As the instrument scans through the magnetic fields, it records the relative abundance of the charged species. The result is a mass spectrum. This spectrum shows the ions detected across the range of molecular weights.

How Mass Spectrometers Sort Ions

mass spectrometry: overview

Mass Spectrometry and Molecular Identity

Mass spectrometry helps identify a compound by measuring its molecular mass and molecular formula. It does this by turning the analyte molecule into ions and then comparing ion abundance with mass-to-charge ratio. One common ionization method is electron ionization, or EI. In EI, high-energy electron beams strike analyte molecules in the gas phase. The beam removes an electron and leaves a molecular ion behind. A molecular ion is a radical cation, so it has a positive charge and an unpaired...

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Isotope Peaks in Mass Spectra

Isotope peaks in mass spectra show how natural isotope mixtures change the signal of a molecule. Most elements occur as a mix of isotopes, which are atoms of the same element with different numbers of neutrons. Because isotopes have different masses, the same fragment can appear at more than one position in a spectrum. The mass of a molecule depends on which isotopes are present in its atoms. The size of each isotope peak also depends on how common those isotopes are in nature. Carbon is a...

mass spectrometry: molecular fragmentation overview

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Mass Spectrometry Fragmentation Patterns

Mass spectrometry fragmentation patterns show how a molecular ion breaks apart after ionization. When a molecule loses an electron inside the mass spectrometer, its structure becomes unstable. The ion then fragments at bonds that often produce the most stable pieces. One common pattern is cleavage of a single bond in the molecular ion. This break forms a radical and a cation. The bond can split in more than one way, but the favored path is the one that gives the more stable carbocation rather...

mass spectrometers

A mass spectrometer sorts charged ions by their mass-to-charge ratio and records their relative abundance. It turns vaporized analyte molecules into ions, separates them, and then measures the signal from each type of ion. The process begins in the ionization chamber. The analyte is in the gas phase inside a vacuum, and it is struck by high-energy electrons. The electrons have about 70 eV of energy, which is enough to remove an electron from the analyte and form a molecular ion. After...

mass spectrum

Reading Peaks in a Mass Spectrum

A mass spectrum shows the charged fragments in an analyte as peaks plotted by mass-to-charge ratio, or m/z. The x-axis gives the mass of each charged fragment divided by the number of charges it carries. The y-axis shows the relative abundance of each charged species based on the signal intensity recorded at the detector. The tallest peak is called the base peak. It is assigned an abundance of 100%, and the other peaks are scaled against it. The peak from the molecular ion is called the parent...

mass spectrum: interpretation

Decoding Molecular Ions in Mass Spectra

Mass spectra help scientists identify an unknown compound by finding the molecular ion peak. The molecular ion peak shows the mass of the intact molecule, but it is often weak or missing because high-energy electron beams cause strong fragmentation. When that happens, a soft-energy electron beam can be used to scan the spectrum and improve the molecular ion signal. Other ionization methods can also give a stronger molecular ion peak. Chemical ionization, field ionization, and desorption...

mass analyzers: overview

Mass Analyzers and Ion Separation

Mass analyzers separate ions by their mass-to-charge ratio, or m/z, in a mass spectrometer. After a sample is vaporized in the ionization chamber, it is hit with a high-energy electron beam. This creates a radical cation and also produces neutral molecules, radicals, and cations. Negatively charged accelerator plates then push the cations into the mass analyzer, where they are sent on to the detector. Several mass analyzer designs are commonly used. These include magnetic sector,...

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Quadrupole, TOF, and Ion Trap Analyzers

Quadrupole, time-of-flight, and ion trap mass analyzers each separate ions in a different way. They are common tools in mass spectrometry and help sort ions by their mass-to-charge ratio, or m/z. A quadrupole mass analyzer uses four cylindrical metal rods arranged in a diamond shape. The rods carry a direct current, or DC, voltage and a radio-frequency AC voltage. Ion motion depends on the field strength, so only ions with a certain m/z resonate and reach the detector at that setting. This...

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Mass Accuracy in HRMS Analysis

High-resolution mass spectrometry separates ions by very small differences in mass. This matters because atomic masses are not always exact whole numbers, even though they are often rounded for simple calculations. Atomic mass is usually estimated by adding the masses of protons and neutrons. In reality, the proton and neutron do not have exactly the same mass. That creates small differences when atomic masses are compared to the simplest hydrogen atom. Helium, for example, is made of 2...

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MS/MS Scan Modes and Fragment Ions

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gas chromatography&ndash;mass spectrometry (gc&ndash;ms)

How GC-MS Separates and Identifies Compounds

Gas chromatography-mass spectrometry (GC-MS) separates compounds in a mixture and then identifies them. A gas chromatograph first splits the mixture into its parts. A mass spectrometer then analyzes each part on its own to determine molecular masses and molecular structures. The gas chromatograph uses a long, narrow capillary column. The inner wall of the column has a polysiloxane coating. This coating serves as the stationary phase. It has a high boiling point, low viscosity, and low polarity.

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ICP-MS Sample Ionization and Detection

ICP-MS uses an inductively coupled plasma torch to turn samples into ions for mass analysis. Solid samples are first dissolved and volatilized before they enter the hot argon plasma. Solution samples are nebulized, which means they are converted into a fine spray, and then passed through the same plasma. Inside the plasma, the analytes break apart. Their atoms become positively charged ions, along with some molecular species. These positive ions are sent to the mass spectrometer, where they...

inductively coupled plasma-mass spectrometry (icp-ms): interferences

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ICP-MS Signal Interference Sources and Fixes

Inductively coupled plasma-mass spectrometry (ICP-MS) is a sensitive method for elemental analysis, but its spectra can be affected by interferences. These interferences can make the mass signal less accurate, even when the instrument is working well. Spectroscopic interferences happen when ions in the plasma have the same mass-to-charge ratio, or m/z, as the analyte ion. This group includes isobaric interferences, polyatomic ion interferences, and refractory oxide ion interferences. Isobaric...

key terms and concepts

Learn how a mass spectrometer ionizes analytes, bends charged ions with a magnetic field, and records a mass spectrum for each molecular weight.

How Mass Spectrometers Sort Ions | JoVE K12

analytical chemistry

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How Mass Spectrometers Sort Ions

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