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The secret weapon of triple quadrupole mass spectrometry: Why can CID improve the sensitivity of molecular detection?
In the field of mass spectrometry, collision-induced dissociation (CID) technology has gained increasing attention and has become an important tool for improving the sensitivity of molecular detection. CID, also known as collision-activated dissociation, can fragment selective ions in the gas phase by collision. This process not only enhances the accuracy of detection, but also allows scientists to analyze the structure of molecules more effectively. .
Basic Principles of CID
CID technology mainly uses electric fields to accelerate ions, increase their kinetic energy, and then collide with neutral gas molecules (such as helium, nitrogen or argon). In this collision, part of the kinetic energy is converted into internal energy, which leads to the breaking of chemical bonds and ultimately the formation of smaller fragment ions. These fragments can be analyzed by mass spectrometry to obtain structural or identification information.
By detecting unique fragment ions, researchers can confirm the presence of precursor ions in the presence of other ions with the same mass-to-charge ratio, which significantly reduces background noise and improves detection limits.
Low Energy and High Energy CID
CID can be divided into low-energy CID and high-energy CID. Low-energy CID is usually performed at kinetic energies below 1 kiloelectronvolt (keV). This method is very effective in dissociating selected precursor ions, but the type of fragments produced is strongly affected by the kinetic energy. Energy CID operates in a higher energy range and can generate certain fragment ions that do not appear in low energy CID.
Architecture of a triple quadrupole mass spectrometer
The triple quadrupole mass spectrometer consists of three quadrupole elements. The first quadrupole (Q1) acts as a mass filter, selectively transmitting the predicted ions into the second quadrupole (Q2), where the gas pressure is higher. High, promoting collision and fragmentation. The fragments are then accelerated into the third quadrupole (Q3) for scanning, and the resulting mass spectrum can be analyzed to obtain structural information or for identification.
Fourier transform ion cyclotron resonance
ICR cells in low-pressure environments can excite ions by applying a pulsed electric field, increasing their kinetic energy. This technique can further re-excite the captured fragment ions to form a multi-stage mass spectrometer (MSn). Determining the fragments produced during the collisions of these excited ions can provide insight into the structure and properties of the molecules.
The sustained off-resonance excitation collision-induced dissociation (SORI-CID) technique allows multiple collisions at low collision energies to further refine the mass spectrometric data.
High Energy Collision Dissociation Technology
High energy collision dissociation (HCD) is designed specifically for orbitrap mass spectrometers. This process is carried out in an additional multipole collision cell, and the generated fragments are then returned to the C-trap for mass analysis. Although the name HCD implies high energy, its actual collision energy is relatively low, usually less than 100 electron volts, which makes it more flexible when introducing labeling for quantitative analysis.
Analysis of fragmentation mechanism
In CID, different fragmentation mechanisms include homolytic and heterolytic cleavage. These dissociation processes help scientists understand the behavior of complex molecules by providing effective structural information. For example, the cleavage of non-adjacent charges can allow researchers to explore how molecules react in different environments, providing insights into mechanistic and materials science.
In this information-driven era, CID technology opens a new window for us to explore the molecular world.
Appropriate use of CID technology can not only increase the sensitivity of molecular detection, but also help scientists capture important information in complex chemical reactions. With the rapid development of mass spectrometry technology, how can we further use CID to develop more sensitive and specific detection methods in the future?
