Quadrupole Mass Filter
Definition and meaning of Quadrupole Mass Filter in chemistry.
A quadrupole mass filter is a mass spectrometer component that separates ions based on their mass-to-charge ratio (m/z) using time-varying electric fields. It consists of four parallel rods with alternating radio frequency and direct current voltages applied to opposite pairs.
In more detail
Ions entering along the central axis experience oscillating electric forces from the radio frequency field. Only ions within a specific m/z range follow stable trajectories and reach the detector; all others collide with the rods and are filtered out. By adjusting both the RF voltage amplitude and the superimposed direct current voltage, the m/z range that passes through can be changed, enabling rapid scanning across different masses. Quadrupole mass filters are favored in analytical chemistry because they are compact, cost-effective, offer good mass resolution for most applications, and can scan a wide m/z range quickly.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Configuration | Four parallel cylindrical or hyperbolic rods in a square arrangement |
| Function | Separates and filters ions by mass-to-charge ratio (m/z) |
| Primary uses | Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) |
In gas chromatography-mass spectrometry (GC-MS) of pesticide residue analysis, a quadrupole mass filter can selectively detect specific molecular ions, enabling identification and quantification of different pesticides in environmental or food samples.
Frequently asked questions
How does changing the RF voltage affect ion transmission?
Increasing the RF voltage amplitude changes which m/z range can pass through the quadrupole, allowing the analyzer to scan across different masses and construct a complete mass spectrum.
What advantage does a quadrupole offer compared to other mass analyzers?
Quadrupoles are relatively inexpensive, compact, provide adequate resolution for most analytical problems, and can rapidly scan a wide m/z range, making them ideal for routine laboratory analysis.