Name: quadrupole, tof, and ion trap analyzers
Uploaded: 2024-04-04T10:51:34.000Z
Duration: 1 min 19 s
Channel: JoVE

L’analyseur de masse quadripolaire se compose de quatre tiges parallèles, à travers lesquelles sont appliquées une tension continue et une tension alternative radiofréquence.
Ici, l’intensité du champ fait que seuls les ions avec des valeurs m/z particulières entrent en résonance avec le champ et frappent le détecteur. Ces analyseurs offrent une faible résolution.
Un autre analyseur courant est l’analyseur de temps de vol, dans lequel le temps de vol des ions est mesuré de la source à travers le tube linéaire sans champ jusqu’au détecteur.
Tous les ions ont à peu près la même énergie cinétique, de sorte que les ions plus légers ont des vitesses plus élevées, ce qui entraîne des temps de vol plus courts.
Pour améliorer la résolution, des réflectrons, ou réflecteurs d’ions, sont utilisés. Ils ralentissent les ions les plus énergétiques, corrigeant les différences d’énergie cinétique entre les ions de même masse.
Une autre alternative est le piège à ions quadripolaire tridimensionnel, composé d’une électrode annulaire et d’une paire d’électrodes d’extrémité. Une tension radiofréquence piège les ions, qui oscillent dans l’anneau.
En augmentant la tension radiofréquence, des ions de plus en plus lourds se stabilisent et s’éjectent sélectivement vers le détecteur.

analyseur de masse : types courants

Mass Analyzers: Common Types

L'analyseur de masse quadripolaire est constitué de quatre tiges métalliques cylindriques disposées en diamant supportant une tension continue et une tension alternative radiofréquence. Le mouvement des ions à travers le quadripôle dépend de l'intensité du champ, ce qui fait que seuls les ions d'un certain m/z résonnent avec succès et frappent le détecteur à une intensité de champ donnée. Bien que le taux de transmission de ces analyseurs soit élevé, la composition élémentaire exacte de l'échantillon n'est pas déterminée en raison de la faible résolution ; cependant, ils sont rentables. La résolution typique d'un analyseur quadripolaire est de 1 Da (ou 1 u).
Dans un analyseur de temps de vol (TOF), le temps de vol d'un ion depuis la source via le tube de dérive linéaire sans champ jusqu'au détecteur est mesuré en microsecondes, et ce temps est converti en une valeur m/z. Les ions pénètrent dans le tube dérive avec à peu près la même quantité d’énergie cinétique. En conséquence, les ions ayant des valeurs m/z différentes se déplacent à des vitesses différentes et atteignent le détecteur à des moments différents. Les ions plus légers se déplacent à une vitesse plus élevée, ce qui entraîne un temps de vol plus court et une résolution relativement médiocre. La résolution peut également être altérée par des différences dans la quantité d’énergie cinétique transmise aux ions, ce qui entraîne des vitesses différentes pour les ions de même m/z. Pour cette raison, un réflectron (ou miroir ionique) est utilisé pour augmenter la distance de déplacement jusqu'au détecteur et ralentir les ions. Les ions plus énergétiques subissent un ralentissement plus important, de sorte que le réflectron corrige la propagation de l'énergie cinétique et offre une meilleure résolution globale. De plus, les analyseurs TOF offrent une sensibilité élevée.
Les analyseurs de pièges à ions quadripolaires tridimensionnels se composent d'une électrode annulaire et de deux électrodes d'extrémité. Une tension radiofréquence piège les ions qui oscillent dans l'anneau. L'augmentation de la tension radiofréquence stabilise les ions plus lourds et les éjecte sélectivement vers le détecteur via les ouvertures situées dans les embouts. Alors que d'autres analyseurs de masse ne permettent qu'à une petite fraction d'ions d'atteindre le détecteur, le piège à ions quadripolaire tridimensionnel permet à la moitié des ions d'atteindre le détecteur, ce qui rend ces analyseurs plus sensibles. Cependant, avec un grand nombre d'ions stockés dans le piège à ions, les effets de charge d'espace entraînent une diminution de la résolution.

Analyseur de masse : types courants

L’analyseur de masse quadripolaire se compose de quatre tiges parallèles, à travers lesquelles sont appliquées une tension continue et une tension alternative radiofréquence.
Ici, le terrain ...

Education

Enseignement

JoVE Core

Analytical Chemistry

Chimie analytique

Unit 1

Unité 1

Principles of Mass Spectrometry

Principes de la spectrométrie de masse

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

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 analyzer has a high transmission rate and is cost-effective, but its low resolution means it does not determine the exact elemental composition of a sample. Its typical resolution is about 1 Da, or 1 u.

A time-of-flight, or TOF, analyzer measures how long ions take to travel from the source through a field-free drift tube to the detector. The flight time is measured in microseconds and converted to an m/z value. Ions enter the tube with about the same kinetic energy, so lighter ions move faster and arrive sooner. That shorter flight time can limit resolution. Resolution can also drop if ions with the same m/z start with different kinetic energies and travel at different speeds.

To improve TOF performance, a reflectron, or ion mirror, can be used. It increases the distance to the detector and slows the ions down. More energetic ions experience a greater slowdown, so the reflectron corrects kinetic energy spread and improves resolution overall. TOF analyzers also offer high sensitivity.

Three-dimensional quadrupole ion-trap analyzers use a ring electrode and two endcap electrodes. A radio-frequency voltage traps the ions so they oscillate in the ring. When the radio-frequency voltage increases, heavier ions become stabilized and are selectively ejected through apertures in the endcaps to the detector. Compared with other mass analyzers that allow only a small fraction of ions to reach the detector, the three-dimensional quadrupole ion trap can send about half of the ions to the detector, which makes it more sensitive. If too many ions are stored, space-charge effects reduce resolution.

Quadrupole, TOF, and Ion Trap Analyzers

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...

mass spectrometry: isotope effect

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

mass-spectrometry-molecular-fragmentation-overview

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

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...

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,...

mass analyzers: common types

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...

high-resolution mass spectrometry (hrms)

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...

mass spectrometry: complex analysis

Hyphenated Mass Spectrometry Methods

Mass spectrometry can be paired with separation methods to study complex mixtures. This combination is called a hyphenated method. It helps when a pure mass spectrum is too hard to read because a mixture causes too much fragmentation and too many overlapping signals. GC-MS is one common hyphenated method. GC stands for gas chromatography, which separates volatile, thermally stable compounds in narrow capillary columns before they enter the mass spectrometer. This approach is widely used in...

tandem mass spectrometry

MS/MS Scan Modes and Fragment Ions

Tandem mass spectrometry uses two or more mass analyzers in series to improve selectivity and lower chemical noise during analyte detection. A set of analyzers separated by an interaction cell lets the instrument break ions apart and study the fragment ions that form. Fragmentation happens in the interaction cell and can be caused in several ways. Collision-induced dissociation, or CID, uses inert gases such as nitrogen, argon, or helium. Other methods include surface-induced dissociation...

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.

inductively coupled plasma&#8211;mass spectrometry (icp&#8211;ms): overview

inductively-coupled-plasmamass-spectrometry-icpms-overview

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

inductively-coupled-plasma-mass-spectrometry-icp-ms-interferences

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 quadrupole, TOF, and ion trap mass analyzers separate ions by m/z, and compare their resolution, sensitivity, and detection methods.

Quadrupole, TOF, and Ion Trap Analyzers | JoVE K12

analytical chemistry

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Quadrupole, TOF, and Ion Trap Analyzers

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