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

Масс-спектрометр ионизирует молекулы и создает масс-спектр из распределения фрагментов.
Он выполняет три функции: ионизацию молекул или атомов, разделение ионных фрагментов и обнаружение ионов.
При ионизации электронов, распространенном методе ионизации, испарившийся образец в ионизационной камере, бомбардируемый высокоэнергетическим электронным пучком, производит радикальные катионы. Катион радикала быстро распадается на нейтральные молекулы, радикалы и катионы.
Затем катионы ускоряются в анализирующую камеру с помощью ряда отрицательно заряженных ускорительных пластин.
Многие распространенные анализаторы прикладывают магнитное или электрическое поле к анализирующей камере, которое изгибает траектории ионов в зависимости от их массы и заряда.
Только ионы с определенными значениями m/z имеют точную траекторию для прохождения через узкую щель, расположенную перед ионным детектором для данного магнитного или электрического поля.
Изменяя поле, масс-анализатор сканирует диапазон ионных масс, при этом их содержание регистрируется в масс-спектре.

Масс-спектрометр

Mass Spectrometers

В этом уроке подробно рассказывается об оборудовании масс-спектрометра — физического прибора для проведения масс-спектрометрии молекул аналитов и записи характеристических масс-спектров. Это достигается за счет трех основных функций:

<ol style="display: flex; flex-direction: column; gap: 10px;">
<li>Преобразование атомов/молекул аналита в газовой фазе в пучок положительно или отрицательно заряженных ионов путем ионизации.</li>
<li>Разделение заряженных частиц на основе отношения их массы к заряду.</li>
<li>Регистрация относительного содержания каждого типа ионов.</li>
</ol>

В ионизационной камере масс-спектрометра испаряющееся аналит в вакууме поражается электронами высокой энергии. Энергия электрона составляет около 70 eV, чего достаточно, чтобы оторвать электрон от аналита. Образующийся молекулярный ион далее фрагментируется на заряженные частицы и нейтральные молекулы. Масс-спектрометр регистрирует только массу заряженных частиц, поскольку заряд позволяет управлять молекулами с помощью электрического или магнитного поля.

Молекулярный ион и его заряженные фрагменты ускоряются серией отрицательно заряженных пластин ускорителя, расположенных соответствующим образом в детекторе в аналитической камере. На путь между пластиной ускорителя и детектором прикладывается магнитное поле, что приводит к искривлению пути заряженных частиц. В постоянном магнитном поле радиус кривизны зависит от молекулярной массы заряженных частиц. Размещение щели перед детектором гарантирует, что только заряженные частицы определенной молекулярной массы попадут в детектор.

Изменяя магнитное поле, на детекторе можно зарегистрировать заряженные частицы всех молекулярных масс, по отдельности каждую уникальную разновидность молекулярной массы. Сканируя все магнитные поля, масс-спектрометр предоставляет информацию об относительном содержании всех заряженных частиц в виде масс-спектра.

На этом уроке подробно описывается приборостроение масс-спектрометра — физического инструмента для выполнения масс-спектрометрии молекул аналита и записи...

Education

JoVE Core

Analytical Chemistry

Аналитическая химия

Unit 1

Раздел 1

Principles of Mass Spectrometry

Принципы масс-спектрометрии

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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

analytical chemistry

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How Mass Spectrometers Sort Ions

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