Name: how mass spectrometers sort ions
Uploaded: 2024-04-04T10:51:33.000Z
Duration: 1 min 16 s
Channel: JoVE

質量分析計は分子をイオン化し、フラグメント分布から質量スペクトルを生成します。
分子や原子のイオン化、イオン断片の分離、イオンの検出の3つの機能を果たします。
一般的なイオン化法である電子イオン化では、イオン化チャンバー内の気化したサンプルに高エネルギーの電子ビームを照射すると、ラジカルカチオンが生成されます。ラジカルカチオンは、すぐに中性分子、ラジカル、およびカチオンに断片化します。
次に、陽イオンは、負に帯電した一連の加速器プレートによって分析チャンバーに加速されます。
多くの一般的な分析装置は、分析チャンバに磁場または電場を印加し、イオンの質量と電荷に基づいてイオンの軌道を曲げます。
特定のm/z値のイオンのみが、特定の磁場または電場に対してイオン検出器の前に配置された狭いスリットを通過する正確な軌道を持っています。
フィールドを変更することにより、質量分析計はさまざまなイオン質量をスキャンし、その存在量を質量スペクトルに記録します。

質量分析計

Mass Spectrometers

このレッスンでは、分析対象分子に対して質量分析を実行し、特徴的な質量スペクトルはを記録する物理的な機器である質量分析計の機器について詳しく説明します。これは、次の 3 つの主な機能によって実現されます。

<ol style="display: flex; flex-direction: column; gap: 10px;">
<li>イオン化による、気相分析物の原子/分子の正または負の荷電イオンのビームへの変換。</li>
<li>質量電荷比に基づいた荷電種の分離。</li>
<li>各種類のイオンの相対存在量を記録します。</li>
</ol>

 質量分析計のイオン化室では、真空中で蒸発した検体に高エネルギー電子が衝突します。電子のエネルギーは約 70 eV で、検体から電子を剥ぎ取るのに十分です。結果として生じる分子イオンは、荷電種と中性分子にさらに断片化されます。電荷により電場または磁場による分子の制御が可能になるため、質量分析計は荷電種の質量のみを記録します。

分子イオンとその荷電フラグメントは、分析チャンバー内の検出器内に適切に配置された一連の負に荷電した加速板によって加速されます。加速板と検出器の間の経路に磁場が印加され、荷電種の経路に曲線が生じます。一定の磁場では、曲率半径は荷電種の分子量に依存します。検出器の前にスリットを配置すると、特定の分子量の荷電種のみが検出器に到達します。

磁場を変化させることにより、すべての分子量の荷電種を、一度にそれぞれ固有の分子量種として検出器で記録することができます。すべての磁場をスキャンすることにより、質量分析計はすべての荷電種の相対存在量に関する情報を質量スペクトルはとして提供します。

このレッスンでは、質量分析計(分析物分子の質量分析を行い、質量分析計を記録するための物理的な装置)の装置について詳しく説明します。

Education

JoVE Core

Analytical Chemistry

分析化学

Unit 1

ユニット1

Principles of Mass Spectrometry

質量分析法の原理

KEY TERMS AND CONCEPTS

主要用語と概念

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 ionization, the molecular ion can break into charged fragments and neutral molecules. The instrument records only the charged species. Their charge allows them to be controlled by electric or magnetic fields.

Next, the molecular ion and its charged fragments are accelerated by a set of negatively charged accelerator plates. These plates move the ions toward the detector in the analyzing chamber. A magnetic field bends the path of the ions as they travel between the accelerator plate and the detector.

At a constant magnetic field, the radius of the curved path depends on the molecular mass of the charged species. A slit placed in front of the detector helps admit only ions with a particular molecular weight. By changing the magnetic field, ions of different molecular weights can reach the detector one at a time.

As the instrument scans through the magnetic fields, it records the relative abundance of the charged species. The result is a mass spectrum. This spectrum shows the ions detected across the range of molecular weights.

How Mass Spectrometers Sort Ions

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

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

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 a mass spectrometer ionizes analytes, bends charged ions with a magnetic field, and records a mass spectrum for each molecular weight.

How Mass Spectrometers Sort Ions | JoVE K12

JoVE Core 分析化学 は、複雑な化学原理をアニメーションで視覚化することで、SI 単位から NMR 分光法を含むトピックをよりわかりやすくします。実験を撮影した実写動画では、これらの概念が世界中の研究所でどのように応用されているかを取り上げています。

analytical chemistry

How Mass Spectrometers Sort Ions

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