Name: using reagent gas in ci mass spectrometry
Uploaded: 2024-12-05T18:32:21.000Z
Duration: 1 min 21 s
Channel: JoVE

Elektron etkisi, kütle spektrometresinde numune moleküllerini iyonize etmek için geleneksel yöntemdir. Bununla birlikte, bazı moleküller için, yüksek enerjili elektron ışını, birincil moleküler iyonun aşırı parçalanmasına neden olur.
Bu tür kütle spektrumlarında moleküler bir iyon zirvesinin olmaması, numunenin tanımlanmasını zorlaştırır.
Alternatif bir kimyasal iyonizasyon yöntemi, ilk olarak numune molekülünün nispeten kararlı eşlenik asidinin oluşturulduğu gaz fazı protonasyon reaksiyonudur. Bu tür daha sonra düşük moleküler ağırlıklı bileşenlere ayrılır. 
Örneğin, di-sec-bütil eterin kimyasal iyonizasyonunu düşünün. Eter, metan gazı ile karıştırılır. Yüksek enerjili bir elektron ışını daha sonra metanı tercihen iyonize eder.
Oluşan metan radikali katyonu, başka bir metan molekülü ile çarpışarak bir metanyum iyonu ve bir metan radikali oluşturur.
Metanyum iyonu bir süper asit ve eteri protonlayan gaz fazında bir proton kaynağıdır. Elektron darbeli iyonizasyon ile oluşturulan moleküler iyon ile karşılaştırıldığında, protonlanmış eter kararlıdır ve kütle spektrumunda M+1 tepe noktasını verir.

kimyasal İyonizasyon (ci) kütle spektrometresi

Chemical Ionization (CI) Mass Spectrometry

Kütle spektrumunda bir molekülün moleküler iyon tepe noktası, moleküler tanımlama için hayati bilgiler sağlar. Ancak, geleneksel elektron darbe iyonizasyonu, bazı moleküler iyonların dedektöre ulaşmadan önce hızla ayrışmasına yol açabilir. Bu tür iyonize analit moleküllerinin ömrünü artırmak için daha hafif bir iyonizasyon yöntemi gereklidir. Kimyasal iyonizasyon (CI), kolayca protonlanarak karşılık gelen konjugat asidi üreten analit moleküllerinin kütle analizinde yararlı bir gaz fazı protonasyon reaksiyonudur. Bu işlemde, numune, elektron darbesinin öncelikle reaktif gaz üzerinde meydana gelmesini sağlayan aşırı bir reaktif gazla karıştırılır. Reaktiften oluşan yüklü türler, analit molekülünü protonlayarak moleküler iyona kıyasla nispeten kararlı bir protonlanmış analit (konjugat asit) üretir. Bu, kütle spektrumunda bir M+1 tepe noktasıyla sonuçlanır. Daha sonra konjugat asit, ek sinyaller üreten parçalanmaya uğrayabilir.

Örneğin, metan gazındaki di-sec-bütil eterin CI'si bu süreci gösterir. Eter, reaktif olarak fazla metan gazıyla karıştırıldığında, elektron çarpması eter yerine metan üzerinde meydana gelir. Ortaya çıkan metan radikal katyonu, bir metan radikali ve bir metan iyonu oluşturmak için başka bir metan molekülüyle reaksiyona girebilir. Metan iyonu, eteri protonlayarak eşlenik asidini oluşturabilen gaz fazı protonlarının bir kaynağıdır. Di-sec-butil eterin kimyasal iyonizasyonu sırasındaki ardışık reaksiyonlar Şekil 1'de gösterilmiştir.

<img alt="Figure1" src="/files/ftp_upload/12300/12300_PT_Figure_1.svg" style="text-align: center; height: 175px;">

Şekil 1: Di-sec-butil eter metan karışımının kimyasal iyonizasyonu.

Eterin bu eşlenik asidi (m/z = 131), geleneksel elektron çarpma iyonizasyonu yoluyla oluşan eterin moleküler iyonundan (m/z = 130) nispeten daha kararlıdır. Geleneksel rotada, moleküler iyon α bölünmesi yoluyla parçalanmaya uğrar ve m/z = 101'de bir sinyal verir. Şekil 2, doğrudan di-sec-bütil eter üzerinde elektron darbe iyonizasyonu sırasında meydana gelen reaksiyonları göstermektedir.

<img alt="Figure2" src="/files/ftp_upload/12300/12300_PT_Figure_2.svg" style="text-align: center; height: 175px;">

Şekil 2: Elektron darbe di-sec-bütil eter iyonizasyonu ve moleküler iyon parçalanması.

Bu nedenle, CI yoluyla iyonize edilen di-sec-bütil eterin kütle spektrumları, m/z = 131'de bir M+1 tepe noktası gösterir. Öte yandan, elektron darbe iyonizasyonu yoluyla iyonize edilen di-sec-bütil eterin kütle spektrumları, moleküler ağırlığının m/z değerinde herhangi bir tepe noktası göstermez. Şekil 3a ve 3b, sırasıyla elektron darbe ve kimyasal iyonizasyon yöntemleri yoluyla iyonize edilen di-sec-butil eterin kütle spektrumlarını göstermektedir.

<img alt="Figure3" src="/files/ftp_upload/12300/12300_PT_Figure_3.svg" style="text-align: center; height: 225px;">

Şekil 3: a) Di-sec-bütil eterin elektron darbe iyonizasyonuyla elde edilen kütle spektrumunda m/z = 130 tepe noktası görünmüyor. b) Di-sec-bütil eterin kimyasal iyonizasyonuyla elde edilen kütle spektrumunda m/z = 131 tepe noktası açıkça görünüyor.

Kimyasal İyonizasyon (CI) Kütle Spektrometresi

Kütle spektrumundaki bir molekülün moleküler iyon zirvesi, moleküler tanımlama için hayati bilgiler sağlar. Bununla birlikte, geleneksel elektron etkisi ...

Education

JoVE Core

Analytical Chemistry

Analitik Kimya

Unit 1

Ünite 1

Mass Spectrometry Fragmentation Methods

Kütle Spektrometrisi Parçalanma Yöntemleri

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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

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Cycloalkene Side-Chain Cleavage in Mass Spectra

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Alkyne Mass Spectra and Key Peaks

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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

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.

Using Reagent Gas in CI Mass Spectrometry

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