Mass spectrometry is a powerful analytical technique that can measure the mass and abundance of molecules in a sample. It can provide information on the identity, structure, and quantity of compounds in various fields, such as pharmaceuticals, food, and life sciences. However, some compounds, such as lipids, have complex structures that are difficult to elucidate by conventional mass spectrometry methods. Lipids are essential components of cell membranes and play important roles in metabolism, signaling, and disease. The function of lipids depends on their chemical structure, especially the position and configuration of double bonds between carbon atoms. However, most mass spectrometry methods cannot distinguish between different types of double bonds, such as cis or trans, or determine their exact location in the molecule.
To overcome this challenge, Shimadzu Corporation has developed a new mass spectrometry technique that can reveal the detailed structure of lipids and other biological compounds. The technique is called oxygen attachment dissociation (OAD), and it is the first in the world to be implemented in a quadrupole time-of-flight (Q-TOF) mass spectrometer. The Q-TOF mass spectrometer is a hybrid instrument that combines a quadrupole mass filter with a time-of-flight mass analyzer. It can achieve high resolution, accuracy, and sensitivity in mass measurements, as well as perform tandem mass spectrometry (MS/MS), which involves breaking down the molecules into smaller fragments and analyzing them separately. The OAD technique adds a new dimension to the MS/MS analysis by selectively breaking the double bonds between carbon atoms using atomic oxygen.
The OAD technique works as follows: First, the sample is ionized by electrospray ionization (ESI), which produces charged droplets of the sample solution. The droplets evaporate and shrink until they release the sample ions into the gas phase. The sample ions are then guided into the quadrupole mass filter, which selects a specific mass-to-charge ratio (m/z) of interest. The selected ions are then transferred to a collision cell, where they collide with a gas, such as argon, and undergo fragmentation. The resulting fragments are called precursor ions, and they contain information on the molecular weight and composition of the sample. The precursor ions are then introduced into the OAD cell, where they react with atomic oxygen. The atomic oxygen is generated by a microwave discharge in a mixture of oxygen and helium gases. The atomic oxygen selectively attaches to the double bonds between carbon atoms and breaks them, producing new fragments called product ions. The product ions are then detected by the time-of-flight mass analyzer, which measures their m/z values and intensities. The product ions contain information on the position and configuration of the double bonds between carbon atoms, which can be used to deduce the structure of the sample.
The OAD technique has several advantages over conventional mass spectrometry methods. First, it can provide structural information that is otherwise difficult or impossible to obtain, such as the location and geometry of double bonds. Second, it can be applied to a wide range of compounds, such as lipids, steroids, terpenes, and natural products, that contain double bonds between carbon atoms. Third, it can be performed in a fast and simple manner, without requiring any chemical derivatization or additional instrumentation. Fourth, it can be integrated with other mass spectrometry techniques, such as liquid chromatography (LC) or ion mobility spectrometry (IMS), to achieve further separation and identification of compounds.
The OAD technique has been successfully applied to various biological samples, such as human plasma, fish oil, and plant extracts, to reveal the structure and diversity of lipids and other natural compounds. The technique has also been used to study the changes in lipid composition and function in response to different stimuli, such as diet, disease, or drug treatment. The OAD technique can thus contribute to the advancement of research and development in the fields of health care and life sciences, by providing a deeper understanding of the molecular mechanisms and interactions of biological compounds.
