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

Pomimo zalet oferowanych przez ICP-MS, na dokładną analizę elementarną mają wpływ zakłócenia spektroskopowe i niespektroskopowe.
Interferencja spektroskopowa jest wywoływana przez jony o takich samych wartościach m/z jak jony analitowe. Do gatunków zakłócających należą formy izobaryczne, jony wieloatomowe i ogniotrwałe jony tlenkowe.
Interferencja izobaryczna powstaje w wyniku izobarów analitu, które są różnymi nuklidami o tej samej liczbie masowej - co oznacza, że wartości m/z są takie same.
Wieloatomowa interferencja jonów wynika z połączenia form plazmy z matrycą lub formami atmosferycznymi w celu utworzenia związków wieloatomowych, które następnie rozpadają się na jony molekularne o tej samej wartości m/z co analit.
Krytyczna interferencja powstaje w wyniku tworzenia się ogniotrwałych form tlenków i wodorotlenków z analitów i matryc. 
Interferencja niespektroskopowa obejmuje efekt matrycy, który jest związany z wysokim stężeniem gatunków matryc i na ogół powoduje redukcję sygnału analitu.
Efekty matrycowe można w dużym stopniu skompensować poprzez zastosowanie odpowiedniego wzorca wewnętrznego.

spektrometria mas ze sprzężoną indukcyjnie plazmą (icp–ms): zakłócenia

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

Spektrometria mas ze sprzężoną plazmą indukcyjnie sprzężoną (ICP–MS) to wysoce selektywna i czuła technika umożliwiająca dokładną analizę elementarną. Chociaż analiza widm masowych ICP–MS jest stosunkowo prosta, wpływają na nią zakłócenia spektroskopowe i niespektroskopowe. Zakłócenia spektroskopowe powstają, gdy plazma zawiera cząsteczki jonowe o wartości m/z takiej samej jak jon analitu. Zakłócenia spektroskopowe można podzielić na zakłócenia izobaryczne, jonów wieloatomowych i ogniotrwałe jonów tlenkowych.

Zakłócenia izobaryczne występują, gdy indukcyjnie sprzężona plazma zawiera izobaryczne formy analitów. Gatunki te są różnymi nuklidami o tej samej liczbie masowej, a zatem mają te same wartości m/z co analit, przy założeniu tego samego ładunku. Na przykład, 40Ar+ i 58Fe+ generalnie pokrywają się z pikami odpowiednio dla 40Ca+ i58Ni+. Przyrządy masowe oparte na kwadrupolach, posiadające rozdzielczość mniejszą niż 1 u, są w znacznym stopniu podatne na zakłócenia izobaryczne. Można go jednak zminimalizować, stosując instrumenty o wyższej rozdzielczości.

Inną interferencję spektroskopową obserwuje się, gdy różne składniki plazmy oddziałują z matrycą lub składnikami atmosfery, tworząc formy wieloatomowe, które mogą ulegać dalszej fragmentacji, tworząc jony molekularne o tej samej wartości m/z co jon analitu. 40ArH+, 16O2+, and 40ArO+ to niektóre potencjalne substancje zakłócające. Korekta ślepej próby lub użycie innego izotopu analitu usuwa takie zakłócenia.

Kolejna krytyczna interferencja występuje, gdy kilka składników analitu i matrycy tworzy tlenki i wodorotlenki, których piki pokrywają się z jonami analitu. Tworzenie się tlenków i wodorotlenków zależy od różnych czynników eksperymentalnych, takich jak natężenie przepływu wtryskiwacza, wielkość kryzy próbki, odstępy odpieniacza próbnika itp. Zakłócenia te są trudniejsze do wyeliminowania niż zakłócenia jonów izobarycznych i wieloatomowych.

Zakłócenia niespektroskopowe obejmują głównie efekt matrycy. Jest to związane z wysokim stężeniem substancji matrycowych — zazwyczaj od 500 do 1000 mg/ml — powodującym redukcję sygnału analitu. Specyficzne warunki eksperymentalne wzmacniają sygnał analitu. Zakłócenia matrycy można wyeliminować poprzez wprowadzenie wewnętrznego standardu o masie i potencjale jonizacyjnym zbliżonym do analitu.

Spektrometria mas ze sprzężoną indukcyjnie plazmą (ICP–MS): Zakłócenia

Pomimo zalet oferowanych przez ICP-MS, na dokładną analizę elementarną mają wpływ zakłócenia spektroskopowe i niespektroskopowe.
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inductively-coupled-plasma-mass-spectrometry-icp-ms-interferences

Education

JoVE Core

Analytical Chemistry

Chemia analityczna

Unit 1

Jednostka 1

Principles of Mass Spectrometry

Zasady spektrometrii mas

KEY TERMS AND CONCEPTS

KLUCZOWE TERMINY I POJĘCIA

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...

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)

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) 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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