Name: hyphenated mass spectrometry methods
Uploaded: 2024-04-04T10:51:34.000Z
Duration: 1 min 21 s
Channel: JoVE

L’analyse de mélanges complexes nécessite la combinaison de méthodes de séparation et de spectrométrie de masse en séquence, appelées méthodes à trait d’union.
La GC-MS est la méthode à trait d’union la plus courante, où un mélange volatil thermiquement stable est séparé par chromatographie en phase gazeuse, et la sortie de la colonne est envoyée en permanence au spectromètre de masse pour ionisation et analyse.
De même, la LC-MS est une chromatographie liquide couplée à un spectromètre de masse.
En règle générale, un mélange contenant des composés polaires ou ioniques non volatils est séparé par chromatographie liquide, et la sortie est ionisée par ionisation par électronébulisation avant d’être envoyée à l’analyseur de masse.
Cependant, les mélanges avec des molécules moins polaires utilisent souvent d’autres méthodes d’ionisation par pression atmosphérique.
La spectrométrie de masse en tandem est une autre méthode hybride d’analyse, où deux analyseurs de masse sont connectés en série.
Contrairement à la GC-MS et à la LC-MS, la spectrométrie de masse en tandem offre une séparation en quelques millisecondes, et elle est plus sensible et sélective.
Il est intéressant de noter que des mélanges très complexes peuvent être analysés en couplant la GC ou la LC avec la spectrométrie de masse en tandem, formant GC-MS/MS et LC-MS/MS.

spectrométrie de masse : analyse complexe

Mass Spectrometry: Complex Analysis

La spectrométrie de masse est une technique importante pour l'identification de composés purs. Cependant, elle présente certaines limites pour l’analyse de mélanges complexes, souvent dues à une fragmentation excessive rendant le spectre trop compliqué à déchiffrer. La spectrométrie de masse peut être combinée avec des méthodes de séparation appropriées en séquence, formant des méthodes avec trait d'union, utiles dans l'analyse de mélanges complexes.

GC-MS est une méthode puissante avec trait d’union couramment utilisée dans les laboratoires médico-légaux et environnementaux pour l’analyse précise des mélanges. La chromatographie en phase gazeuse utilise des colonnes capillaires étroites pour séparer les composants d'un mélange volatil thermiquement stable et les transmet au spectromètre de masse pour analyse.

LC-MS est une autre méthode couplée qui associe la chromatographie liquide à un spectromètre de masse pour analyser les mélanges non volatils. Pour rendre la chromatographie liquide compatible avec un spectromètre de masse, des interfaces d'ionisation à maintien de pression appropriées ou des techniques d'ionisation à pression atmosphérique telles que l'ionisation par électropulvérisation, qui s'applique aux composés polaires et ioniques, ou l'ionisation chimique à pression atmosphérique, qui s'applique aux molécules moins polaires, sont utilisées.

Une autre méthode hybride, appelée spectroscopie de masse en tandem, utilise plusieurs analyseurs de masse en séquence. Comparée à d’autres méthodes avec trait d’union, la spectroscopie tandem est plus rapide, plus sensible et plus sélective en raison d’un bruit chimique plus faible. La spectroscopie tandem peut être combinée avec des techniques de séparation pour former GC-MS/MS ou LC-MS/MS pour une analyse de mélange plus complexe.

L'électrophorèse capillaire-spectrométrie de masse est une technique très sensible couramment utilisée pour analyser de grosses biomolécules comme l'ADN, les protéines et les polypeptides. Cette méthode alimente les analyseurs de masse quadripolaires en effluents capillaires après passage à travers une interface d'ionisation par électrospray ou ESI.

Spectrométrie de masse : analyse complexe

L’analyse de mélanges complexes nécessite la combinaison de méthodes de séparation et de spectrométrie de masse en séquence, appelées méthodes à trait d’union.
GC-MS ...

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

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 forensic and environmental laboratories for precise mixture analysis.

LC-MS is another important option for nonvolatile mixtures. LC stands for liquid chromatography, and it must be linked to the mass spectrometer with pressure-maintaining ionization interfaces or atmospheric-pressure ionization methods. Electrospray ionization works well for polar and ionic compounds, while atmospheric-pressure chemical ionization is used for less polar molecules.

Tandem mass spectroscopy uses multiple mass analyzers in sequence. Compared with other hyphenated methods, it is faster, more sensitive, and more selective because it creates less chemical noise. Tandem methods can also be combined with separation steps to form GC-MS/MS or LC-MS/MS for even more complex samples.

Capillary electrophoresis-mass spectrometry is another sensitive hybrid technique. It is commonly used to analyze large biomolecules such as DNA, proteins, and polypeptides. In this method, capillary effluents pass through an electrospray ionization interface and into quadrupole mass analyzers.

Hyphenated Mass Spectrometry Methods

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, 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

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 GC-MS, LC-MS, tandem mass spectroscopy, and capillary electrophoresis-mass spectrometry help analyze complex mixtures in forensic, environmental, and biomolecule studies.

Hyphenated Mass Spectrometry Methods | JoVE K12

analytical chemistry

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Hyphenated Mass Spectrometry Methods

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