Name: isotope peaks in mass spectra
Uploaded: 2025-12-12T12:30:35.000Z
Duration: 1 min 13 s
Channel: JoVE

分子内のほとんどの原子は、異なる同位体として発生する可能性があり、その結果、異なる原子量が得られます。したがって、マススペクトルには、これらの違いに対応するマスシグナルが含まれています。
さまざまな同位体からの質量シグナルの位置は、それらの質量差によって決まります。質量シグナルの相対強度は、一般に同位体の相対的な存在量に依存します。
例えば、炭素含有分子は、分子イオンのピークよりも1単位高い13Cから追加のピークを示します。この追加のピークは、M + 1ピークとして知られています。
炭素原子の数が増えると、13Cを含む可能性が高くなり、M+1ピークの相対強度が増加します。
塩化物と臭化物の質量スペクトルは、第一級塩素と臭素の同位体が2質量単位異なるため、M+2シグナルを示します。
M+2 ピークの相対強度は、分析種分子中の塩素か臭素かを特定するのに役立ちます。

質量分析:同位体効果

Mass Spectrometry: Isotope Effect

ほとんどの元素は、同位体の混合物として自然界に存在します。同位体は、それぞれの中性子の数により重量が異なります。分子の分子量は、関与する元素の特定の同位体によって異なります。その結果、分子の質量スペクトルは、同じフラグメントの複数の位置でピークを示します。これらの質量シグナルの位置は、分子量の違いによって異なります。さらに、これらのシグナルの強度は、自然界の同位体存在量の相対的な比率に依存します。
例えば、炭素には、分子量12と13 uの2つの安定な天然同位体があり、これらは1:0.011の相対組成で共存しています。炭素含有分子イオンまたは荷電フラグメントの質量シグナルは、その分子量(M)と分子量(M+1)より1単位高い位置にあります。M+1 ピークと M ピークの相対的な比率は、特定の分子内の炭素原子の数によって異なります。メタン、デカン、イコサンのMピークとM+1ピークを比較します。炭素原子の数が増えると、分子が13C原子を含む可能性が高くなるため、M+1ピークの相対強度も増加します。
質量スペクトルの同位体ピークとその相対強度は、未知の分析種中の特定の元素の存在を特定するために使用されます。例えば、分子内のM+2ピークは、ハロゲン化物の同位体が2u異なるため、分子内に塩素または臭素が存在することを示します。さらに、M+2ピークの相対強度から、分析種中の塩素と臭素を区別することができます。塩素同位体の存在量は 35Cl の 75%、37Cl の 25% ですが、臭素同位体は 79Br と 81Br の約 50% です。クロロベンゼンとブロモベンゼンの質量スペクトルにおける M ピークと M+2 ピークの相対比の違いは注目に値します。

ほとんどの元素は、同位体の混合物として自然界に存在します。同位体は、それぞれの中性子の数により重量が異なります。の分子量...

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

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 useful example. It has two stable isotopes, 12 and 13 u, in a relative composition of 1:0.011.

For carbon-containing ions, the main signal appears at M, which is the molecular mass. A second signal appears at M+1. The size of the M+1 peak compared with the M peak depends on how many carbon atoms the molecule has. Methane, decane, and icosane show this trend clearly. As the number of carbon atoms increases, the M+1 peak becomes more intense because there is a greater chance of including a 13C atom.

Isotope peaks can also help identify specific elements in an unknown analyte. An M+2 peak often points to chlorine or bromine, because their isotopes differ by two u. The relative intensity of that M+2 peak can help distinguish between them. Chlorine is about 75% 35Cl and 25% 37Cl, while bromine is about 50% 79Br and 81Br. This difference creates distinct M to M+2 patterns, such as those seen in chlorobenzene and bromobenzene.

Isotope Peaks in Mass Spectra

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 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

Hyphenated Mass Spectrometry Methods

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tandem mass spectrometry

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 isotope peaks appear in mass spectra, why carbon gives M and M+1 signals, and how M+2 peaks can reveal chlorine or bromine.

Isotope Peaks in Mass Spectra | 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

Isotope Peaks in Mass Spectra

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