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

Moleküllerdeki çoğu atom, farklı izotoplar olarak ortaya çıkabilir ve bu da farklı atom kütlelerine neden olabilir. Dolayısıyla, kütle spektrumu bu farklılıklara karşılık gelen kütle sinyallerini içerir.
Çeşitli izotoplardan gelen kütle sinyallerinin konumları, kütle farkları ile belirlenir. Kütle sinyallerinin nispi yoğunlukları genellikle izotopların nispi bolluğuna bağlıdır.
Örneğin, karbon içeren moleküller, moleküler iyon zirvesinden bir birim daha yüksek olan 13C'den ek bir tepe gösterir. Bu ek tepe noktası, M+1 tepe noktası olarak bilinir.
Karbon atomlarının sayısındaki bir artış, 13C'yi dahil etmek için daha fazla şans verir ve böylece M + 1 tepe noktasının nispi yoğunluğunu arttırır.
Klorürlerin ve bromürlerin kütle spektrumları, birincil klor ve brom izotopları iki kütle birimi ile farklılık gösterdiğinden, bir M+2 sinyali sergiler.
M+2 tepe noktalarının nispi yoğunlukları, analit molekülünde klor mu yoksa brom mu olduğunu belirlemeye yardımcı olur.

kütle spektrometresi: İzotop etkisi

Mass Spectrometry: Isotope Effect

Çoğu element doğada izotopların bir karışımı olarak bulunur. İzotoplar, ilgili nötron sayıları nedeniyle ağırlıkları farklıdır. Bir molekülün moleküler ağırlığı, ilgili elementlerinin spesifik izotopuna bağlı olarak farklıdır. Sonuç olarak, molekülün kütle spektrumu, aynı parçadan birden fazla pozisyonda zirveler sergiler. Bu kütle sinyallerinin konumları, moleküler kütle arasındaki farka bağlıdır. Ayrıca, bu sinyallerin yoğunluğu, doğadaki izotopik bolluğun nispi oranına bağlıdır.
Örneğin, karbon, 1:0.011'lik bir nispi bileşimde bir arada bulunan moleküler kütle 12 ve 13 u'luk iki kararlı, doğal olarak oluşan izotopa sahiptir. Karbon içeren bir moleküler iyon veya yüklü bir parça için kütle sinyalleri, moleküler kütlesinde (M) ve moleküler kütlesinden (M+1) bir birim daha yüksekte konumlandırılır. M+1 tepe noktasının M tepe noktasına nispi oranı, belirli moleküldeki karbon atomlarının sayısına bağlıdır. Metan, dekan ve ikosan'ın M ve M+1 zirveleri karşılaştırılır. Karbon atomlarının sayısı arttıkça, molekülün 13C atomu içerme olasılığının artması nedeniyle M+1 zirvesinin nispi yoğunluğu da artar.
Kütle spektrumundaki izotop zirveleri ve bunların nispi yoğunluğu, bilinmeyen analitteki belirli elementlerin varlığını tanımlamak için kullanılır. Örneğin, moleküldeki bir M+2 zirvesi, molekülde klor veya brom varlığını gösterir, çünkü halojenürlerin izotopları iki u farklıdır. Ek olarak, M+2 tepe noktasının nispi yoğunluğundan, analitteki klor ve brom arasında ayrım yapmak mümkündür. Klor izotoplarının bolluğu 35Cl'nin %75'i ve 37Cl'nin %25'i iken, brom izotopları için 79Br ve 81Br'nin yaklaşık %50'sidir. Klorobenzen ve bromobenzenin kütle spektrumlarındaki M ve M+2 pikleri arasındaki nispi orandaki fark dikkat çekicidir.

Kütle Spektrometresi: İzotop Etkisi

Çoğu element doğada izotopların bir karışımı olarak bulunur. İzotoplar, ilgili nötron sayıları nedeniyle ağırlıkları farklıdır. Moleküler ağırlığı ...

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JoVE Core

Analytical Chemistry

Analitik Kimya

Unit 1

Ünite 1

Principles of Mass Spectrometry

Kütle Spektrometrisi İlkeleri

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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

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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...

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Hyphenated Mass Spectrometry Methods

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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

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inductively coupled plasma&#8211;mass spectrometry (icp&#8211;ms): overview

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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

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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 Analitik Kimya, karmaşık kimyasal prensiplerini anlaşılır, ilgi çekici animasyonlara dönüştürerek basitleştirir ve SI Birimlerinden NMR spektroskopisine kadar konuları daha erişilebilir ve anlaşılır hale getirir. Buna ek olarak, bilim insanlarının yer aldığı videolar, bu kavramların dünya çapındaki laboratuvarlarda yürütülen gerçek dünya araştırmalarındaki uygulamalarını gösterir.

analytical chemistry

Isotope Peaks in Mass Spectra

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