Name: quadrupole, tof, and ion trap analyzers
Uploaded: 2024-04-04T10:51:34.000Z
Duration: 1 min 19 s
Channel: JoVE

The quadrupole mass analyzer consists of four parallel rods, across which are applied a DC voltage and a radio-frequency AC voltage.
Here, the field strength causes only ions with particular m/z values to resonate with the field and strike the detector. These analyzers offer a low resolution.
Another common analyzer is the time-of-flight analyzer, wherein ion flight time is measured from the source through the linear field-free tube to the detector.
All ions have about the same kinetic energy, so lighter ions have higher velocities, resulting in shorter flight times.
To improve the resolution, reflectrons, or ion reflectors, are used. They slow down the more energetic ions, correcting kinetic energy differences between ions of the same mass.
Another alternative is the three-dimensional quadrupole ion trap, consisting of a ring electrode and a pair of endcap electrodes. A radio-frequency voltage traps the ions, which oscillate in the ring.
By increasing the radio-frequency voltage, progressively heavier ions stabilize and selectively eject to the detector.

mass analyzers: common types

Mass Analyzers: Common Types

The quadrupole mass analyzer consists of four cylindrical metal rods arranged in a diamond carrying a DC voltage and a radio-frequency AC voltage. The motion of ions through the quadrupole depends on the field strength, causing only ions of a certain m/z to resonate successfully and strike the detector at a given field strength. Though the transmission rate for these analyzers is high, the exact elemental composition of the sample is not determined because of low resolution; however, they are cost-effective. The typical resolution of a quadrupole analyzer is 1 Da (or 1 u).
In a time-of-flight (TOF) analyzer, the flight time of an ion from the source through the linear field-free drift tube to the detector is measured in microseconds, and this time is converted to an m/z value. The ions enter the drift tube with about the same amount of kinetic energy. Accordingly, ions with different m/z values travel with different velocities and reach the detector at different times. Lighter ions travel with higher velocity, resulting in a shorter time-of-flight and comparatively poor resolution. Resolution can also be impaired by differences in the amount of kinetic energy imparted to the ions, causing ions of the same m/z to have different velocities. Because of this, a reflectron (or ion mirror) is employed to increase the travel distance to the detector and slow down the ions. More energetic ions experience greater slowdown, so the reflectron corrects the kinetic energy spread and provides a better resolution overall. In addition, TOF analyzers offer high sensitivity.
Three-dimensional quadrupole ion-trap analyzers consist of a ring electrode and two endcap electrodes. A radio-frequency voltage traps the ions, which oscillate in the ring. Increasing the radio-frequency voltage stabilizes heavier ions and selectively ejects them to the detector via apertures in the endcaps. While other mass analyzers allow only a small fraction of ions to reach the detector, the three-dimensional quadrupole ion trap enables half of the ions to reach the detector, making these analyzers more sensitive. However, with a large number of ions stored in the ion trap, the space-charge effects result in decreased resolution.

The quadrupole mass analyzer consists of four parallel rods, across which are applied a DC voltage and a radio-frequency AC voltage.
Here, the field ...

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Principles of Mass Spectrometry

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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 analyzer has a high transmission rate and is cost-effective, but its low resolution means it does not determine the exact elemental composition of a sample. Its typical resolution is about 1 Da, or 1 u.

A time-of-flight, or TOF, analyzer measures how long ions take to travel from the source through a field-free drift tube to the detector. The flight time is measured in microseconds and converted to an m/z value. Ions enter the tube with about the same kinetic energy, so lighter ions move faster and arrive sooner. That shorter flight time can limit resolution. Resolution can also drop if ions with the same m/z start with different kinetic energies and travel at different speeds.

To improve TOF performance, a reflectron, or ion mirror, can be used. It increases the distance to the detector and slows the ions down. More energetic ions experience a greater slowdown, so the reflectron corrects kinetic energy spread and improves resolution overall. TOF analyzers also offer high sensitivity.

Three-dimensional quadrupole ion-trap analyzers use a ring electrode and two endcap electrodes. A radio-frequency voltage traps the ions so they oscillate in the ring. When the radio-frequency voltage increases, heavier ions become stabilized and are selectively ejected through apertures in the endcaps to the detector. Compared with other mass analyzers that allow only a small fraction of ions to reach the detector, the three-dimensional quadrupole ion trap can send about half of the ions to the detector, which makes it more sensitive. If too many ions are stored, space-charge effects reduce resolution.

Quadrupole, TOF, and Ion Trap Analyzers

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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...

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key terms and concepts

Learn how quadrupole, TOF, and ion trap mass analyzers separate ions by m/z, and compare their resolution, sensitivity, and detection methods.

Quadrupole, TOF, and Ion Trap Analyzers | JoVE K12

analytical chemistry

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Quadrupole, TOF, and Ion Trap Analyzers

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