Name: icp-ms signal interference sources and fixes
Uploaded: 2024-04-04T10:51:35.000Z
Duration: 1 min 20 s
Channel: JoVE

Apesar das vantagens oferecidas pelo ICP-MS, a análise elementar precisa é afetada por interferências espectroscópicas e não espectroscópicas.
A interferência espectroscópica é causada por íons com os mesmos valores m/z que os íons do analito. As espécies interferentes incluem espécies isobáricas, íons poliatômicos e íons de óxido refratários.
A interferência isobárica surge das isóbaras do analito, que são nuclídeos diferentes que têm o mesmo número de massa, o que significa que os valores de m/z são os mesmos.
A interferência de íons poliatômicos resulta da combinação de espécies de plasma com matrizes ou espécies atmosféricas para formar espécies poliatômicas que se fragmentam em íons moleculares com o mesmo valor m/z de um analito.
Uma interferência crítica surge devido à formação de espécies refratárias de óxido e hidróxido a partir das espécies de analito e matriz. 
A interferência não espectroscópica inclui o efeito de matriz, que está associado a uma alta concentração de espécies de matriz e geralmente causa redução do sinal do analito.
Os efeitos da matriz podem ser amplamente compensados usando um padrão interno apropriado.

espectrometria de massa-plasma acoplada indutivamente (icp-ms): interferências

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS): Interferences

A espectrometria de massa com plasma indutivamente acoplado (ICP-MS) é uma técnica altamente seletiva e sensível para análise elementar precisa. Embora a análise dos espectros de massa ICP-MS seja comparativamente simples, ela é afetada por interferências espectroscópicas e não-espectroscópicas. As interferências espectroscópicas surgem quando o plasma contém espécies iônicas com um valor m/z igual ao do íon analito. A interferência espectroscópica pode ser categorizada como interferências isobáricas, de íons poliatômicos e de íons de óxido refratário.

A interferência isobárica ocorre quando o plasma acoplado indutivamente contém espécies isobáricas de analitos. Essas espécies é nuclídeos diferentes com o mesmo número de massa e, portanto, possuem os mesmos valores m/z do analito, assumindo a mesma carga. Por exemplo, 40Ar+ e 58Fe+ geralmente se sobrepõem aos picos de 40Ca+ e 58Ni+, respectivamente. Instrumentos de massa baseados em quadrupolos, com resolução inferior a 1 u, é substancialmente afetados pela interferência isobárica. No entanto, isso pode ser minimizado usando instrumentos de maior resolução.

Outra interferência espectroscópica é observada quando vários componentes do plasma interagem com a matriz, ou componentes atmosféricos, para formar espécies poliatômicas, que podem sofrer fragmentação adicional para formar íons moleculares com o mesmo valor m/z do íon analito. 40ArH+, 16O2+, e 40ArO+ é alguns potenciais interferentes. Uma correção em branco, ou o uso de um isótopo de analito diferente, remove tais interferências.

Outra interferência crítica ocorre quando vários componentes do analito e da matriz formam óxidos e hidróxidos cujos picos se sobrepõem aos íons do analito. A formação de óxidos e hidróxidos depende de vários fatores experimentais, como a vazão do injetor, o tamanho do orifício da amostra, o espaçamento do skimmer do amostrador, etc. Essas interferências é mais difíceis de eliminar do que as interferências de íons isobáricos e poliatômicos.

As interferências não-espectroscópicas incluem principalmente o efeito de matriz. Este efeito está associado a uma alta concentração de espécies de matriz – geralmente, 500 a 1000 mg/mL – causando redução do sinal do analito. Condições experimentais específicas melhoram o sinal do analito. As interferências da matriz podem ser eliminadas incorporando um padrão interno com massa e potencial de ionização próximos ao do analito.

Espectrometria de Massa-Plasma Acoplada Indutivamente (ICP-MS): Interferências

Apesar das vantagens oferecidas pelo ICP-MS, a análise elementar precisa é afetada por interferências espectroscópicas e não espectroscópicas.
...

inductively-coupled-plasma-mass-spectrometry-icp-ms-interferences

Education

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidade 1

Principles of Mass Spectrometry

Princípios da Espectrometria de Massas

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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 interference occurs when different nuclides share the same mass number and therefore the same m/z value if the charge is the same. For example, 40 Ar+ can overlap with 40 Ca+, and 58 Fe+ can overlap with 58 Ni+.

Quadrupole-based mass instruments, which have a resolution of less than 1 u, are strongly affected by isobaric interference. Using a higher-resolution instrument can help reduce this problem. Polyatomic interferences can appear when plasma species react with matrix or atmospheric components to form molecular ions. Examples include 40 ArH+, 16 O2+, and 40 ArO+.

These polyatomic interferences can be reduced with a blank correction or by choosing a different analyte isotope. Another important spectroscopic problem is the formation of oxides and hydroxides. These peaks can overlap with analyte ions. Their formation depends on experimental conditions such as injector flow rate, sample orifice size, and sampler-skimmer spacing. These interferences are often harder to remove than isobaric and polyatomic interferences.

Non-spectroscopic interferences mainly involve the matrix effect. A matrix is the other material in the sample, and a high matrix concentration of about 500 to 1000 mg/mL can reduce the analyte signal. Certain experimental conditions can improve the analyte signal. Matrix interference can also be reduced by using an internal standard with a mass and ionization potential close to the analyte.

ICP-MS Signal Interference Sources and Fixes

icp-ms-signal-interference-sources-and-fixes

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...

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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...

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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)

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

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...

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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) 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 ICP-MS signals can be affected by isobaric, polyatomic, oxide, and matrix interferences, and how blank correction and internal standards help.

ICP-MS Signal Interference Sources and Fixes | JoVE K12

analytical chemistry

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ICP-MS Signal Interference Sources and Fixes

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