A quadrupole is an integral part of a quadrupole mass spectrometer, which is a tool used to identify and quantify the makeup of a sample. The quadrupole is composed of four metal rods that are arranged in a rectangular pattern. Each rod is charged either positively or negatively with radio frequency (RF) and a DC component. The amount of RF and DC that is applied to rods determines which molecular weight is allowed through the mass filter.
When a sample is put into the quadrupole mass spectrometer, it is ionized first. This means that atoms or molecules in the sample have their electrons removed, creating charged particles known as ions. These ions are then accelerated through the quadrupole by an electric field (as described above) and directed towards a detector at the other end.
The quadrupole functions as a mass filter, allowing ions with a specific mass-to-charge ratio to pass through while rejecting ions with different mass-to-charge ratios. This allows the instrument to selectively detect and measure ions of specific masses. The quadrupole can be adjusted to pass ions of different mass-to-charge ratios by changing the voltage on the rods. This can be performed at very high speeds, allowing for rapid analysis times.
Quadrupole mass spectrometers are used in a wide range of industries, such as environmental analysis, food and beverage testing, and pharmaceuticals. They are known for their high sensitivity and ability to accurately measure trace levels of contaminants.