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 is applied between one pair of rods and the other. A direct current voltage is then superimposed on the RF voltage. Ions travel down the quadrupole between the rods. Only ions of a certain mass-to-charge ratio m/z 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 Hill differential equation.
Ideally the rods are hyperbolic. Circular 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.
Read more about this topic: Quadrupole Mass Analyzer
Famous quotes containing the words principle of, principle and/or operation:
“Thou art blind to the danger of marrying a woman who feels and acts out the principle of equal rights.”
—Angelina Grimké (1805–1879)
“We have been here over forty years, a longer period than the children of Israel wandered through the wilderness, coming to this Capitol pleading for this recognition of the principle that the Government derives its just powers from the consent of the governed. Mr. Chairman, we ask that you report our resolution favorably if you can but unfavorably if you must; that you report one way or the other, so that the Senate may have the chance to consider it.”
—Anna Howard Shaw (1847–1919)
“It requires a surgical operation to get a joke well into a Scotch understanding. The only idea of wit, or rather that inferior variety of the electric talent which prevails occasionally in the North, and which, under the name of “Wut,” is so infinitely distressing to people of good taste, is laughing immoderately at stated intervals.”
—Sydney Smith (1771–1845)