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

El analizador de masas cuadrupolar consta de cuatro varillas paralelas, a través de las cuales se aplican un voltaje de CC y un voltaje de CA de radiofrecuencia.
Aquí, la intensidad del campo hace que solo los iones con valores particulares m/z resuenen con el campo y golpeen el detector. Estos analizadores ofrecen una baja resolución.
Otro analizador común es el analizador de tiempo de vuelo, en el que el tiempo de vuelo de los iones se mide desde la fuente a través del tubo lineal sin campo hasta el detector.
Todos los iones tienen aproximadamente la misma energía cinética, por lo que los iones más ligeros tienen velocidades más altas, lo que resulta en tiempos de vuelo más cortos.
Para mejorar la resolución, se utilizan reflectores o reflectores de iones. Ralentizan los iones más energéticos, corrigiendo las diferencias de energía cinética entre iones de la misma masa.
Otra alternativa es la trampa de iones cuadrupolar tridimensional, que consta de un electrodo de anillo y un par de electrodos de tapa. Un voltaje de radiofrecuencia atrapa los iones, que oscilan en el anillo.
Al aumentar el voltaje de radiofrecuencia, los iones progresivamente más pesados se estabilizan y expulsan selectivamente al detector.

analizador de masas: tipos comunes

Mass Analyzers: Common Types

El analizador de masas cuadrupolo consta de cuatro varillas metálicas cilíndricas dispuestas en forma de diamante que transportan una tensión continua y una tensión alterna de radiofrecuencia. El movimiento de los iones a través del cuadrupolo depende de la intensidad del campo, lo que hace que solo los iones de una determinada m/z resuenen con éxito y golpeen el detector con una intensidad de campo determinada. Aunque la velocidad de transmisión de estos analizadores es alta, la composición elemental exacta de la muestra no se determina debido a la baja resolución; sin embargo, son rentables. La resolución típica de un analizador cuadrupolo es 1 Da (o 1 u).

En un analizador de tiempo de vuelo (TOF), el tiempo de vuelo de un ion desde la fuente a través del tubo de deriva lineal sin campo hasta el detector se mide en microsegundos, y este tiempo se convierte a un valor m/z. Los iones ingresan al tubo de deriva con aproximadamente la misma cantidad de energía cinética. En consecuencia, los iones con diferentes valores de m/z viajan con diferentes velocidades y llegan al detector en diferentes momentos. Los iones más ligeros viajan a mayor velocidad, lo que da como resultado un tiempo de vuelo más corto y una resolución comparativamente pobre. La resolución también puede verse afectada por diferencias en la cantidad de energía cinética impartida a los iones, lo que hace que los iones del mismo m/z tengan diferentes velocidades. Debido a esto, se emplea un reflectrón (o espejo de iones) para aumentar la distancia de viaje hasta el detector y ralentizar los iones. Los iones más energéticos experimentan una mayor desaceleración, por lo que el reflectrón corrige la dispersión de energía cinética y proporciona una mejor resolución general. Además, los analizadores TOF ofrecen una alta sensibilidad.

Los analizadores de trampa de iones cuadrupolo tridimensionales constan de un electrodo de anillo y dos electrodos de extremo. Una tensión de radiofrecuencia atrapa los iones, que oscilan en el anillo. El aumento del voltaje de radiofrecuencia estabiliza los iones más pesados ​​y los expulsa selectivamente al detector a través de aberturas en las tapas de los extremos. Mientras que otros analizadores de masas permiten que solo una pequeña fracción de iones llegue al detector, la trampa de iones cuadrupolo tridimensional permite que la mitad de los iones llegue al detector, lo que hace que estos analizadores sean más sensibles. Sin embargo, con una gran cantidad de iones almacenados en la trampa de iones, los efectos de la carga espacial dan como resultado una resolución disminuida.

Analizador de masas: Tipos comunes

El analizador de masas cuadrupolar consta de cuatro varillas paralelas, a través de las cuales se aplican un voltaje de CC y un voltaje de CA de radiofrecuencia.
Aquí, el campo ...

Education

Educación

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidad 1

Principles of Mass Spectrometry

Principios de la espectrometría de masas

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

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...

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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

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...

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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...

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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.

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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