Name: using reagent gas in ci mass spectrometry
Uploaded: 2024-12-05T18:32:21.000Z
Duration: 1 min 21 s
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전자 충격은 질량 분석법에서 샘플 분자를 이온화하는 기존의 방법입니다. 그러나 일부 분자의 경우 고에너지 전자빔이 1차 분자 이온의 과도한 단편화를 일으킵니다.
이러한 질량 스펙트럼에 분자 이온 피크가 없기 때문에 샘플을 식별하기가 어렵습니다.
대안적인 화학 이온화 방법은 기체상 양성자화 반응이며, 먼저 샘플 분자의 비교적 안정적인 접합산이 생성됩니다. 그런 다음 이 종은 저분자량 성분으로 분열됩니다. 
예를 들어, di-sec-butyl ether의 화학적 이온화를 고려하십시오. 에테르는 메탄 가스와 혼합됩니다. 그런 다음 고 에너지 전자빔은 메탄을 우선적으로 이온화합니다.
형성된 메탄 라디칼 양이온은 다른 메탄 분자와 충돌하여 메탄 이온과 메탄 라디칼을 생성합니다.
메탄 이온은 초산이며 에테르를 양성자화하는 기체 상 양성자의 공급원입니다. 전자 충격 이온화에 의해 형성된 분자 이온과 비교할 때 양성자화된 에테르는 안정적이어서 질량 스펙트럼에서 M+1 피크를 제공합니다.

화학 이온화(ci) 질량 분석법

Chemical Ionization (CI) Mass Spectrometry

질량 스펙트럼에서 분자의 분자 이온 피크는 분자 식별에 중요한 정보를 제공합니다. 그러나 기존의 전자 충격 이온화는 일부 분자 이온이 검출기에 도달하기 전에 빠르게 해리될 수 있습니다. 이러한 이온화된 분석 물질 분자의 수명을 늘리려면 보다 온화한 이온화 방법이 필요합니다. 화학 이온화(CI)는 쉽게 양성자화되어 상응하는 짝산을 생성하는 분석 분자를 질량 분석하는 데 유용한 기상 양성자화 반응입니다. 이 과정에서 샘플은 과잉 시약 가스와 혼합되어 주로 시약 가스에 전자 충격이 발생합니다. 시약에서 형성된 하전된 종은 분석물 분자를 양성자화하여 분자 이온에 비해 상대적으로 안정적인 양성자화된 분석물(공액산)을 생성합니다. 이로 인해 질량 스펙트럼에서 M+1 피크가 발생합니다. 그 다음 공액산은 추가적인 신호를 생성하는 단편화를 겪을 수 있습니다.

예를 들어, 메탄 가스 내 di-sec-부틸 에테르의 CI는 이 과정을 보여줍니다. 에테르가 시약인 과량의 메탄 가스와 혼합되면 에테르가 아닌 메탄에 전자 충격이 발생합니다. 생성된 메탄 라디칼 양이온은 다른 메탄 분자와 반응하여 메탄 라디칼과 메탄 이온을 생성할 수 있습니다. 메탄 이온은 에테르를 양성자화하여 짝산을 형성할 수 있는 기상 양성자의 공급원입니다. di-sec-부틸 에테르의 화학적 이온화 동안의 순차적 반응은 그림 1에 묘사되어 있습니다.

<img alt="Figure1" src="/files/ftp_upload/12300/12300_PT_Figure_1.svg" style="height: 175px;">

그림 1: 디초-부틸 에테르 메탄 혼합물의 화학적 이온화.

이 에테르의 짝산(m/z = 131)은 기존의 전자 충격 이온화를 통해 형성된 에테르의 분자 이온(m/z = 130)보다 상대적으로 더 안정적입니다. 전통적인 경로에서 분자 이온은 α 절단을 통해 단편화되어 m/z = 101에서 신호를 제공합니다. 그림 2는 di-sec-부틸 에테르에서 직접 전자 충격 이온화 중에 발생하는 반응을 보여줍니다.

<img alt="Figure2" src="/files/ftp_upload/12300/12300_PT_Figure_2.svg" style="height: 175px;">

그림 2: 전자 충격 디초부틸 에테르 이온화 및 분자 이온 단편화.

따라서 CI를 통해 이온화된 di-sec-부틸 에테르의 질량 스펙트럼은 m/z = 131에서 M+1 피크를 나타냅니다. 반면, 전자 충격 이온화를 통해 이온화된 di-sec-부틸 에테르의 질량 스펙트럼은 표시되지 않습니다. 분자량의 m/z 값에 있는 모든 피크. 그림 3a와 3b는 각각 전자 충격 방법과 화학적 이온화 방법을 통해 이온화된 di-sec-부틸 에테르의 질량 스펙트럼을 보여줍니다.

<img alt="Figure3" src="/files/ftp_upload/12300/12300_PT_Figure_3.svg" style="height: 225px;">

그림 3: a) di-sec-부틸 에테르의 전자 충격 이온화를 통해 얻은 질량 스펙트럼에는 m/z = 130 피크가 표시되지 않습니다. b) m/z = 131 피크는 di-sec-부틸 에테르의 화학적 이온화를 통해 얻은 질량 스펙트럼에서 명확하게 볼 수 있습니다.

화학 이온화(CI) 질량 분석법

질량 스펙트럼에 있는 분자의 분자 이온 피크는 분자 식별을 위한 중요한 정보를 제공합니다. 그러나 기존의 전자 충격은 ...

Education

교육

JoVE Core

Analytical Chemistry

분석 화학

Unit 1

제1단원

Mass Spectrometry Fragmentation Methods

질량 분석법의 단편화 방법

KEY TERMS AND CONCEPTS

주요 용어 및 개념

using reagent gas in ci mass spectrometry

Chemical ionization mass spectrometry uses a reagent gas to help detect molecules that break apart too quickly in electron impact ionization. It is a milder ionization method that can extend the life of the ionized analyte, which makes molecular identification easier.

In chemical ionization, the sample is mixed with an excess reagent gas. This setup makes the electron impact occur mainly on the reagent gas instead of on the analyte. The charged species formed from the reagent then protonates the analyte molecule and forms a stable conjugate acid.

The protonated analyte is usually more stable than the original molecular ion. As a result, the mass spectrum often shows an M+1 peak. The conjugate acid can still fragment and produce extra signals.

The chemical ionization of di-sec-butyl ether in methane shows this process clearly. Methane acts as the reagent gas, and electron impact first creates a methane radical cation. That species reacts further to form a methanium ion, which donates a gas-phase proton to the ether and forms its conjugate acid.

The protonated di-sec-butyl ether appears at m/z = 131 and is more stable than the molecular ion at m/z = 130. With conventional electron impact ionization, the molecular ion fragments by alpha cleavage and gives a signal at m/z = 101. In the mass spectrum, CI shows the M+1 peak at m/z = 131, while electron impact ionization does not show a peak at the molecular weight of the ether.

Using Reagent Gas in CI Mass Spectrometry

using-reagent-gas-in-ci-mass-spectrometry

mass spectrometry: long-chain alkane fragmentation

mass-spectrometry-long-chain-alkane-fragmentation

Mass Spectra of Linear Alkane Chains

Mass spectra of linear alkanes show a clear fragmentation pattern. The molecular ion often breaks at a carbon-carbon bond away from the end of the chain. This cleavage forms a stable carbocation and a stable radical, so the middle of the mass-to-charge plot usually has the strongest signals while the ends are weaker. As each bond breaks, a methyl group is lost and the main peaks in the spectrum appear 14 u apart. Smaller peaks near each main signal can also appear. These come from secondary...

mass spectrometry: branched alkane fragmentation

mass-spectrometry-branched-alkane-fragmentation

Branched Alkanes in Mass Spectra

Branched alkanes in mass spectrometry fragment quickly because branching can create stable carbocations. When cleavage happens at a branching point, a secondary or tertiary carbocation may form. That stability helps explain why the molecular ion peak is often very weak or missing compared with a linear alkane. The lesson uses 2-methylbutane, neopentane, and n-pentane to show how this pattern appears in mass spectra. 2-methylbutane and neopentane break apart to form secondary and tertiary...

mass spectrometry: cycloalkane fragmentation

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Cycloalkane Ions and Mass Peaks

Cycloalkane ions in mass spectrometry often give strong peaks because the ring structure helps stabilize the molecular ion. Compared with linear or branched alkanes, this added stability changes how the molecule breaks apart. As a result, cycloalkanes can produce prominent signals in the mass spectrum. Cyclohexane is a clear example. Its molecular ion has an m/z of 84, and this peak is often stronger than the signal from hexane, a linear alkane. The closed ring helps hold the ion together,...

mass spectrometry: alkene fragmentation

Alkene Ion Fragmentation Patterns

Alkene ion fragmentation patterns in mass spectrometry begin when the molecule loses one electron from the unsaturated π bond. This ionization forms a stable molecular ion. The ion can then break apart by three main reaction pathways. The most common pathway is cleavage at the allylic position, which is the carbon next to the double bond. This produces an allylic carbocation that is stabilized by resonance. In terminal alkenes, this fragment appears at a mass-to-charge ratio of 41. In internal...

mass spectrometry: cycloalkene fragmentation

mass-spectrometry-cycloalkene-fragmentation

Cycloalkene Side-Chain Cleavage in Mass Spectra

Cycloalkenes can break apart in a mass spectrometer through retro-Diels–Alder fragmentation. In this process, two carbon-carbon bonds in the ring split, and ethene is released. The remaining fragment is a dienyl radical cation that is 28 u less than the molecular ion. This pathway is similar to the fragmentation of cycloalkanes that also releases ethene. The difference is the type of charged fragment that remains. Cycloalkanes form an alkyl species, while cycloalkenes form a dienyl species.

mass spectrometry: alkyne fragmentation

Alkyne Mass Spectra and Key Peaks

Alkyne mass spectra often show strong peaks from two main fragmentation paths. One path breaks the carbon-carbon bond between the alpha and beta carbons of the alkyne bond. This produces a 3-propynyl cation, also called a propargyl cation. In terminal alkynes, this is the only fragmentation path that gives the 3-propynyl cation. The unsubstituted 3-propynyl cation appears at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne forms a...

mass spectrometry: alcohol fragmentation

Alcohol Fragmentation Patterns in Mass Spectra

Alcohols fragment in mass spectrometry in predictable ways. When an alcohol, written as R-OH, ionizes, it can lose one non-bonded electron from the oxygen atom. That forms a molecular ion, but the molecular ion peak is often weak or may not appear because alcohols break apart quickly. Two main fragmentation routes are important for alcohols: β-cleavage and dehydration. In β-cleavage, the bond at the β-position next to the hydroxyl group breaks. This gives a resonance-stabilized cation and a...

mass spectrometry: aromatic compound fragmentation

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Mass Spectra of Benzene and Toluene

Mass spectra of aromatic compounds show a strong molecular ion peak. In ionization, the molecule becomes a molecular ion, which appears as a prominent peak in the spectrum. Benzene gives a molecular ion at m/z 78, and toluene gives one at m/z 92. Benzene’s molecular ion is especially stable. It does not fragment readily because breaking the aromatic benzene ring requires a large amount of energy. Alkyl-substituted benzenes behave differently in mass spectrometry. Toluene can lose a hydrogen...

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Amines in Mass Spectra: Nitrogen Rule

Amines can be identified in mass spectrometry by their fragmentation patterns and by the nitrogen rule. The molecular ions of amines often break apart through β-cleavage, which cuts a carbon-carbon bond next to the nitrogen. This process forms an alkyl radical and a resonance-stabilized nitrogen-containing cation. The nitrogen rule helps predict the mass of the molecular ion. A compound with one nitrogen atom, or any odd number of nitrogen atoms, gives a molecular ion with an odd molecular...

mass spectrometry: alkyl halide fragmentation

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Mass Spectra of Alkyl Halides

Mass spectra of alkyl halides show clear isotope patterns from the halogen atom. Chlorine has two common isotopes, 35Cl and 37Cl, in a 3:1 ratio. Bromine has two common isotopes, 79Br and 81Br, in a 1:1 ratio. These isotope ratios create two molecular ion peaks, [M] and [M + 2], with relative heights that match the halide abundance. This pattern is easy to see in examples such as 2-chloropropane and 1-bromopropane. 2-Chloropropane gives peaks in a 3:1 ratio. 1-Bromopropane gives peaks in a 1:1...

mass spectrometry: aldehyde and ketone fragmentation

mass-spectrometry-aldehyde-and-ketone-fragmentation

Carbonyl Fragment Patterns in Mass Spectra

Aliphatic aldehydes and ketones break apart in mass spectrometry through a few key carbonyl fragment patterns. The main pathways are alpha-cleavage, inductive cleavage, and the McLafferty rearrangement. These patterns help chemists read the mass spectrum and spot a carbonyl group. Alpha-cleavage is a common break next to the carbonyl group. The bond beside the carbonyl splits, and this forms an alkyl radical and an acylium cation. The acylium cation is often seen in the spectrum because it is...

mass spectrometry: carboxylic acid, ester, and amide fragmentation

mass-spectrometry-carboxylic-acid-ester-and-amide-fragmentation

Mass Spectra of Carboxylic Compounds

Mass spectra of carboxylic acids, esters, and amides often show two key fragmentation routes: β-cleavage and McLafferty rearrangement. In β-cleavage, the carbon-carbon bond at the β-position next to the carboxylic group breaks. This produces a neutral radical and a cation. Long-chain compounds can also fragment by McLafferty rearrangement if they have a hydrogen on the γ-carbon. The γ-carbon is the third carbon away from the carboxylic group. This rearrangement gives a radical cation and a...

chemical ionization (ci) mass spectrometry

Chemical ionization mass spectrometry uses a reagent gas to help detect molecules that break apart too quickly in electron impact ionization. It is a milder ionization method that can extend the life of the ionized analyte, which makes molecular identification easier. In chemical ionization, the sample is mixed with an excess reagent gas. This setup makes the electron impact occur mainly on the reagent gas instead of on the analyte. The charged species formed from the reagent then protonates...

electrospray ionization (esi) mass spectrometry

electrospray-ionization-esi-mass-spectrometry

How ESI Turns Biomolecules Into Ions

Electrospray ionization, or ESI, is a mass spectrometry method used to detect biomolecules that are too large or nonvolatile for conventional electron impact ionization. These molecules may break down before they can ionize or evaporate. ESI helps prevent rapid fragmentation and lets scientists record a mass signal for the whole biomolecule. ESI uses electrical energy to move ions from the liquid phase into the gas phase. The analyte biomolecule is mixed with an ionic liquid, which is a...

matrix-assisted laser desorption ionization (maldi)

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How MALDI Turns Samples Into Ions

Matrix-assisted laser desorption ionization (MALDI) is a mass spectrometry technique that turns biomolecules into ions for analysis. It is used to identify and characterize proteins, peptides, nucleic acids, and carbohydrates. Because of this, it is common in biological and medical research, as well as pharmacology and biochemistry. In MALDI, the analyte of interest is mixed with a matrix material. The matrix is usually an organic compound, such as a small organic acid or a crystalline...

key terms and concepts

See how chemical ionization uses a reagent gas to protonate analytes, form a stable conjugate acid, and produce an M+1 peak in mass spectra.

Using Reagent Gas in CI Mass Spectrometry | JoVE K12

analytical chemistry

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Using Reagent Gas in CI Mass Spectrometry

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