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Quadrupole mass analyzer
The quadrupole mass analyzer (QMS) is one type of mass analyzer used in mass spectrometry. It is also known as a transmission quadrupole mass spectrometer, quadrupole mass filter, or quadrupole mass spectrometer. As the name implies, it consists of four cylindrical rods, set parallel to each other. In a quadrupole mass spectrometer the quadrupole is the component of the instrument responsible for filtering sample ions, based on their mass-to-charge ratio (''m/z''). Ions are separated in a quadrupole based on the stability of their trajectories in the oscillating electric fields that are applied to the rods.〔
==Principle of operation==
The quadrupole consists of four parallel metal rods. Each opposing rod pair is connected together electrically, and a radio frequency (RF) voltage with a DC offset voltage is applied between one pair of rods and the other. Ions travel down the quadrupole between the rods. Only ions of a certain mass-to-charge ratio will reach the detector for a given ratio of voltages: other ions have unstable trajectories and will collide with the rods. This permits selection of an ion with a particular ''m/z'' or allows the operator to scan for a range of ''m/z''-values by continuously varying the applied voltage.〔 Mathematically this can be modeled with the help of the Mathieu differential equation.
Ideally, the rods are hyperbolic. Cylindrical rods with a specific ratio of rod diameter-to-spacing provide an easier-to-manufacture adequate approximation to hyperbolas. Small variations in the ratio have large effects on resolution and peak shape. Different manufacturers choose slightly different ratios to fine-tune operating characteristics in context of anticipated application requirements. In recent decades some manufacturers have produced quadrupole mass spectrometers with true hyperbolic rods.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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