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

L'analisi di miscele complesse richiede la combinazione di metodi di separazione e spettrometria di massa in sequenza, denominati metodi con trattino.
GC-MS è il metodo sillabato più comune, in cui una miscela volatile termicamente stabile viene separata mediante gascromatografia e l'output della colonna viene continuamente inviato allo spettrometro di massa per la ionizzazione e l'analisi.
Allo stesso modo, la LC-MS è una cromatografia liquida accoppiata a uno spettrometro di massa.
Tipicamente, una miscela con composti polari o ionici non volatili viene separata mediante cromatografia liquida e l'output viene ionizzato mediante ionizzazione elettrospray prima di essere inviato all'analizzatore di massa.
Tuttavia, le miscele con molecole meno polari utilizzano spesso altri metodi di ionizzazione a pressione atmosferica.
La spettrometria di massa tandem è un altro metodo ibrido per l'analisi, in cui due analizzatori di massa sono collegati in serie.
A differenza della GC-MS e della LC-MS, la spettrometria di massa tandem offre una separazione in millisecondi ed è più sensibile e selettiva.
È interessante notare che miscele altamente complesse possono essere analizzate accoppiando GC o LC con la spettrometria di massa tandem, formando GC-MS/MS e LC-MS/MS.

spettrometria di massa: analisi complessa

Mass Spectrometry: Complex Analysis

La spettrometria di massa è una tecnica importante per l'identificazione di composti puri. Tuttavia presenta alcune limitazioni per l'analisi di miscele complesse, spesso dovute ad un'eccessiva frammentazione che rende lo spettro troppo complicato da decifrare. La spettrometria di massa può essere combinata con opportuni metodi di separazione in sequenza, formando metodi con trattino, utili nell'analisi di miscele complesse.

GC–MS è un potente metodo con trattino comunemente utilizzato nei laboratori forensi e ambientali per l'analisi precisa delle miscele. La gascromatografia utilizza colonne capillari strette per separare i componenti di una miscela volatile termicamente stabile e li passa allo spettrometro di massa per l'analisi.

LC-MS è un altro metodo con trattino che accoppia la cromatografia liquida con uno spettrometro di massa per analizzare miscele non volatili. Per rendere la cromatografia liquida compatibile con uno spettrometro di massa, sono necessarie interfacce di ionizzazione con mantenimento della pressione o tecniche di ionizzazione a pressione atmosferica come la ionizzazione elettrospray, applicabile per composti polari e ionici, o la ionizzazione chimica a pressione atmosferica, applicabile a molecole meno polari. usato.

Un altro metodo ibrido, chiamato spettroscopia di massa tandem, utilizza più analizzatori di massa in sequenza. Rispetto ad altri metodi con trattino, la spettroscopia tandem è più veloce, più sensibile e più selettiva grazie al minore rumore chimico. La spettroscopia tandem può essere ulteriormente combinata con tecniche di separazione per formare GC–MS/MS o LC–MS/MS per analisi di miscele più complesse.

La spettrometria capillare elettroferesi-massa è una tecnica molto sensibile comunemente utilizzata per analizzare biomolecole di grandi dimensioni come DNA, proteine e polipeptidi. Questo metodo alimenta gli analizzatori di massa quadrupolare con effluenti capillari dopo aver attraversato un'interfaccia di ionizzazione elettrospray.

Spettrometria di massa: analisi complessa

L'analisi di miscele complesse richiede la combinazione di metodi di separazione e spettrometria di massa in sequenza, denominati metodi con trattino.
GC-MS ...

Education

Didattica

JoVE Core

Analytical Chemistry

Chimica Analitica

Unit 1

Unità 1

Principles of Mass Spectrometry

Principi della spettrometria di massa

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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