Name: mass accuracy in hrms analysis
Uploaded: 2024-04-04T10:51:34.000Z
Duration: 1 min 15 s
Channel: JoVE

12C 동위원소를 제외하고, 원소 핵의 질량은 정수에 가깝지만 정확하지는 않습니다.
그러나 질량 스펙트럼은 일반적으로 입자 질량을 가장 가까운 정수로 반올림한 것으로 표시하며, 이를 공칭 원자 또는 분자 질량이라고 합니다.
이 근사치는 단지 소수점만 다른 유사한 분자 질량을 가진 분자를 구별하는 것을 어렵게 한다.
예를 들어, 사이클로펜타논과 사이클로헥산은 가장 가까운 정수로 반올림할 때 동일한 공칭 분자량을 갖습니다. 이러한 분자는 고분해능 질량 분석법을 사용하여 구별할 수 있습니다.
HRMS는 좁은 자기장 스테이지를 사용하여 0.0001 통일 원자 질량 단위의 정확도로 입자 질량을 감지합니다. 고해상도 질량 분석법으로 결정된 질량은 정확한 분자 질량으로 알려져 있습니다.
정확한 분자 질량의 세부사항은 동일한 명목상 분자 질량을 가진 분자를 구별하기 위하여 이용될 수 있습니다. 이것은 차례로 샘플의 분자 공식을 식별하는 데 도움이 됩니다.

고분해능 질량분석법(hrms)

High-Resolution Mass Spectrometry (HRMS)

질량 분석기의 분해능은 이온 질량이 서로 다른 이온을 분리하는 효율성에 따라 달라집니다. 원자의 질량은 양성자와 중성자의 질량을 동일하게 간주하여 내부의 양성자와 중성자의 질량의 합으로 근사화됩니다. 그러나 양성자(1.6726 × 10−24g)와 중성자(1.6749 × 10−24g)의 질량은 실제로 동일하지 않습니다. 가장 단순한 수소 원자에 대한 원자 질량 표현에는 사소한 오류가 있습니다. 예를 들어, 헬륨의 질량(양성자 2개 + 중성자 2개)은 정확히 수소 질량(양성자 1개)의 4배가 아닙니다. 또한, 다수의 핵자가 핵 내에 갇혀 있으면 위치 에너지가 증가하고 질량이 감소합니다(질량과 에너지의 상호 변환으로 인해). 이는 두 경우 모두 양성자와 중성자의 총 개수가 동일함에도 불구하고 중수소(2H) 원자 6개의 질량에 비해 12C의 질량이 더 낮은 이유입니다. 원자 질량은 종종 자유 바닥 상태 12C 원자의 나머지 질량을 12로 나눈 것으로 정의되는 통일 원자 질량 단위(u)로 표현됩니다. (통일 원자 질량 단위는 기호 Da를 사용하여 달톤으로도 알려져 있습니다. 종종 'amu'라는 기호를 사용하여 '원자 질량 단위'로 불리며, 이는 통일 원자 질량 단위로 대체된 산소 기반 유사한 단위의 이름과 기호였습니다.)

자유 바닥 상태의 정지 상태 12C를 제외한 모든 원자핵의 경우 정확한 원자 질량은 정수가 아닙니다. 결과적으로, 분자 질량은 반드시 정수일 필요는 없습니다. 일반적으로 원자 및 분자 질량은 가장 가까운 정수(명목 질량이라고 함)로 근사화됩니다. 주어진 동위원소의 질량은 또한 동위원소의 질량을 원자 질량 상수(1u와 동일)로 나눈 상대 질량으로 표현될 수도 있습니다. Table 1에는 다양한 동위원소의 상대 질량, 정확한 질량, 공칭 질량이 나열되어 있습니다.

<table style="margin-left: auto; margin-right: auto;">
	<tbody>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">동위 원소</td>
			<td style="color: black; border: 1px solid black; text-align: center;">양성자의 수</td>
			<td style="color: black; border: 1px solid black; text-align: center;">중성자 수</td>
			<td style="color: black; border: 1px solid black; text-align: center;">상대 질량</td>
			<td style="color: black; border: 1px solid black; text-align: center;">정확한 질량</td>
			<td style="color: black; border: 1px solid black; text-align: center;">공칭질량</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">1H</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1</td>
			<td style="color: black; border: 1px solid black; text-align: center;">0</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1.0078 u</td>
			<td style="color: black; border: 1px solid black; text-align: center;">1 u</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">4He</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">2</td>
			<td style="color: black; border: 1px solid black; text-align: center;">4</td>
			<td style="color: black; border: 1px solid black; text-align: center;">4.0026 u</td>
			<td style="color: black; border: 1px solid black; text-align: center;">4 u</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">12C</td>
			<td style="color: black; border: 1px solid black; text-align: center;">6</td>
			<td style="color: black; border: 1px solid black; text-align: center;">6</td>
			<td style="color: black; border: 1px solid black; text-align: center;">12</td>
			<td style="color: black; border: 1px solid black; text-align: center;">12.0000 u</td>
			<td style="color: black; border: 1px solid black; text-align: center;">12 u</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">14N</td>
			<td style="color: black; border: 1px solid black; text-align: center;">7</td>
			<td style="color: black; border: 1px solid black; text-align: center;">7</td>
			<td style="color: black; border: 1px solid black; text-align: center;">14</td>
			<td style="color: black; border: 1px solid black; text-align: center;">14.0032 u</td>
			<td style="color: black; border: 1px solid black; text-align: center;">14 u</td>
		</tr>
		<tr>
			<td style="color: black; border: 1px solid black; text-align: center;">16O</td>
			<td style="color: black; border: 1px solid black; text-align: center;">8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">8</td>
			<td style="color: black; border: 1px solid black; text-align: center;">16</td>
			<td style="color: black; border: 1px solid black; text-align: center;">15.9949 u</td>
			<td style="color: black; border: 1px solid black; text-align: center;">16 u</td>
		</tr>
	</tbody>
</table>

Table 1: 가장 풍부한 수소, 헬륨, 탄소, 질소 및 산소 동위원소의 상대 질량, 정확한 질량 및 명목 질량.

일반 질량 분석기는 최소 1 u만큼 다른 이온을 구별할 수 있습니다. 이는 동일한 공칭 질량 값을 가진 서로 다른 분자를 구별하는 데 어려움을 초래합니다. 시클로펜타논과 시클로헥산의 예를 생각해 보세요. 둘 다 공칭 분자량이 84u로 동일합니다. 그러나 정확한 분자 질량, 화학 구조 및 원자 수는 다릅니다(사이클로펜타논: (CH2)4CO, 84.0573 u; 사이클로헥산: C6H1184.0573 u). 그러나 고분해능 질량 분석기는 0.0001 u 정도만 다른 이온도 구별할 수 있습니다. 고해상도 질량 분석기는 미세한 자기장 단계를 사용하여 분석 방에서 하전된 화학종을 스캔합니다. 미세한 단계는 정확한 분자량에 따라 이온의 경로를 편향시켜 유사한 분자량을 가진 이온을 분리하는 데 효율적입니다.

고분해능 질량분석법(HRMS)

질량 분석기의 분해능은 이온 질량이 다른 이온을 분리하는 효율성에 따라 달라집니다. 원자의 질량은 다음과 같습니다.

Education

교육

JoVE Core

Analytical Chemistry

분석 화학

Unit 1

제1단원

Principles of Mass Spectrometry

질량 분석법의 원리

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 protons and 2 neutrons, but its mass is not exactly four times the mass of hydrogen.

Mass can also change because of energy inside the nucleus. When many nucleons are packed together, potential energy increases and mass decreases through mass-energy interconversion. This is why 12C has a lower mass than six deuterium atoms, even though both contain the same total number of protons and neutrons.

Atomic masses are commonly given in unified atomic mass units, or u. This unit is defined as one-twelfth of the rest mass of a free, ground-state 12C atom. It is also called the dalton, or Da. The older term amu was used for a similar oxygen-based unit that has been replaced.

For most nuclei other than free, ground-state, at-rest 12C, the exact atomic mass is not a whole number. That means molecular mass is not always a whole number either. Scientists often round to the nearest whole number and call that the nominal mass. The mass of an isotope can also be written as a relative mass, which is the isotope mass divided by the atomic mass constant, equal to 1 u. Table 1 shows relative mass, exact mass, and nominal mass for common isotopes such as 1H, 4He, 12C, 14N, and 16O.

Normal mass spectrometers usually separate ions that differ by at least 1 u. That can make it hard to tell apart molecules with the same nominal mass. Cyclopentanone and cyclohexane are one example. Both have a nominal molecular mass of 84 u, but their exact masses, structures, and atom counts are different. Cyclopentanone is (CH2)4CO at 84.0573 u, while cyclohexane is C6H11 at 84.0936 u.

A high-resolution mass spectrometer can separate ions that differ by only 0.0001 u. It uses very small magnetic field steps in the analyzing chamber to scan charged species. These fine steps deflect ions according to exact molecular weight and help distinguish compounds with very similar masses.

Mass Accuracy in HRMS Analysis

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

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)

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

Explore how high-resolution mass spectrometry separates ions by exact mass, distinguishes isotopes, and tells apart molecules with the same nominal mass.

Mass Accuracy in HRMS Analysis | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Mass Accuracy in HRMS Analysis

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