Name: mass analyzers and ion separation
Uploaded: 2024-04-04T10:51:34.000Z
Duration: 1 min 13 s
Channel: JoVE

Los analizadores de masas comunes incluyen analizadores de sector magnético, de doble enfoque, cuadrupolo, de tiempo de vuelo y de trampa de iones.
La capacidad de cualquier analizador de masas se puede evaluar por su resolución, que describe la capacidad de diferenciar iones con relaciones masa-carga similares.
La resolución se expresa como la relación entre el valor nominal m/z de un pico y la diferencia resoluble más pequeña entre él y un pico adyacente. Los factores limitantes para la resolución del analizador dependen del tipo de analizador.
Por ejemplo, un simple analizador de sector magnético necesita que los iones tengan aproximadamente la misma energía cinética cuando entran en el campo magnético, de modo que los iones con diferentes valores m/z se desvían de forma fiable a diferentes trayectorias.
Por lo tanto, incluso las pequeñas variaciones de energía cinética causadas durante la fragmentación y la aceleración hacen que esta separación sea menos efectiva.
Sin embargo, un analizador de doble enfoque emplea un sector de campo eléctrico aplicado adicional para corregir las diferencias de energía cinética, lo que puede dar un aumento de hasta diez veces en la resolución.

analizadores de masas: descripción general

Mass Analyzers: Overview

El analizador de masas es un componente crucial del espectrómetro de masas. En la cámara de ionización, la muestra vaporizada se bombardea con un haz de electrones de alta energía para generar un catión radical y fragmentarlo aún más en moléculas, radicales y cationes neutros. Una serie de placas aceleradoras cargadas negativamente aceleran los cationes hacia el analizador de masas. El analizador de masas separa los iones según sus relaciones masa-carga (m/z) y luego los dirige al detector. Los tipos comunes de analizadores de masas incluyen sector magnético, doble enfoque, cuadrupolo, tiempo de vuelo y trampa de iones.

Se aplica un campo magnético en el analizador del sector magnético y las cargas en movimiento se desvían siguiendo una trayectoria curva. Para un campo magnético dado, el radio de curvatura depende del valor m/z, y los iones de un valor m/z particular pasan al detector. Como resultado, el campo magnético del instrumento varía continuamente para pasar secuencialmente iones en un rango m/z más amplio al detector.

Un analizador de masas de doble enfoque utiliza una combinación del sector electrostático y el sector magnético. A medida que los iones salen de la fuente, el campo electrostático enfoca el haz iónico para minimizar la dispersión de energía cinética y luego conduce los iones al sector magnético. El sector magnético clasifica los iones según la desviación. Este doble enfoque del haz ayuda a lograr una alta resolución.

La resolución del espectrómetro de masas se define como su capacidad para diferenciar entre dos espectros de masas muy próximos entre sí. Una resolución unitaria indica la capacidad del instrumento para diferenciar masas con una diferencia de una unidad entera. Por ejemplo, un instrumento con resolución unitaria puede distinguir m/z 50 de m/z 51, o m/z 100 de m/z 101, o m/z 500 de m/z 501. Generalmente, la resolución de los espectrómetros comerciales es en el rango de 500 a 500.000.

Analizadores de masas: descripción general

Los analizadores de masas comunes incluyen analizadores de sector magnético, de doble enfoque, cuadrupolo, de tiempo de vuelo y de trampa de iones.
La capacidad de cualquier analizador de masas ...

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

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, double-focusing, quadrupole, time-of-flight, and ion trap analyzers. In a magnetic sector analyzer, a magnetic field bends the moving ions into a curved path. The radius of that curve depends on the ion's m/z value. By changing the magnetic field, the instrument can pass ions with different m/z values to the detector one after another.

A double-focusing mass analyzer combines an electrostatic sector and a magnetic sector. As ions leave the source, the electrostatic field focuses the beam and reduces the spread in kinetic energy. The beam then enters the magnetic sector, which separates the ions by deflection. This double-focusing design helps the instrument achieve high resolution.

Resolution describes how well a mass spectrometer can tell apart two closely spaced mass spectra. Unit resolution means the instrument can distinguish masses that differ by one integer unit, such as m/z 50 and 51, or 100 and 101, or 500 and 501. In commercial spectrometers, resolution is generally in the range of 500 to 500,000.

Mass Analyzers and Ion Separation

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 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, 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...

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

See how mass analyzers separate ions by m/z, how magnetic sector and double-focusing designs work, and what resolution means in mass spectrometry.

Mass Analyzers and Ion Separation | JoVE K12

analytical chemistry

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Mass Analyzers and Ion Separation

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