What Is a Time of Flight Mass Spectrometer?

Time of Flight Mass Spectrometer (TOF) is a very common type of mass spectrometer. The mass analyzer of this mass spectrometer is an ion drift tube. The ions generated by the ion source accelerate into the field-free drift tube and fly towards the ion receiver at a constant speed. The larger the ion mass, the longer it takes to reach the receiver, the smaller the ion mass, and the shorter the time to reach the receiver. According to this principle, ions of different masses can be separated according to the m / z value.

Time-of-flight mass spectrometer is a mass spectrometer that establishes a mass spectrum by ions reaching a detector at different mass-charge ratios at different times in a vacuum-free field-free area at a certain distance. A classic linear time-of-flight mass spectrometer includes an ion source, a flight tube, a detector and recording system, and a vacuum system. Compared with conventional mass spectrometers, it has the advantages of simple structure, high ion flux, and unlimited mass range. It was only in the 1940s that the resolution was limited to about 100 due to the limitation of instrument design and electronic technology. In the 1950s, Wiley and Malarin designed spatial focus and timelag focus ion sources, and the resolution increased to several hundred. In the 1970s, Mamyfin and Karataev designed ion mirrors, which further solved the problem of ion energy dispersion and put time-of-flight mass spectrometers into the ranks of high-resolution instruments. Due to the development of electronic technology in the 1990s and the further application of time-lapse focusing technology, commercial laser time-of-flight mass spectrometers have reached a resolution of more than 10,000, and the application range has become wider. In the late 1980s, Kams and Hillenkamp discovered matrix-assisted laser desorption ionization mass spectrometry, which achieved a major breakthrough in the analysis of biological macromolecules and made it an important tool for life science research. By the 21st century, various types of functional time-of-flight mass spectrometers have been introduced, such as electrospray ionization, glow discharge ionization, GC / MS, LC / MS, and capillary electrophoresis. The main function of the mass spectrometer. Time-of-flight mass spectrometer has been regarded as a promising high-performance mass spectrometer. ^[1]

flight duration

The principle of a time-of-flight mass spectrometer is to measure the time it takes for an ion to reach the detector from the ion source. This process involves generating ion beams in the ion source, then accelerating and measuring their time from the ion source to the detector. There is a drift tube in between, usually about 2m long, as shown in Figure 6-7. All ions receive the same kinetic energy in the acceleration region, but their masses are different, so their speeds are different, and the time to reach the detector (TOF) through the drift tube is also different. So there are:

It can be seen that lighter ions have higher velocities and heavier ions have slower velocities. If the distance from the ion source to the detector is L, then

Obviously, the m / z value of an ion is determined by the time it takes to reach the detector.

The time-of-flight mass spectrometer scans fast, and the time required to record a mass spectrum is in microseconds. This instrument has a wide mass range and can measure ions above m / z 10,000. ^[2]

Because ATOFMS can identify the special compounds that make up particulate matter, it can provide a new perspective to examine the dynamic chemical processes between particles and the surrounding gas and other particulate matter. Real-time chemical composition analysis eliminates traditional

The application of time-of-flight mass spectrometer in environmental monitoring mainly includes the following aspects:

Particle classification: particle composition can be classified according to the mass spectrum characteristics of the particles, and the narrow aerodynamic diameter of the particles can be used to classify the particles; it can also be used to classify the combination of particle size and particle chemical composition at the same time. Corresponding relationship.

Number concentration change: Analyze the change of particle number concentration with time; you can analyze the number concentration of different particle diameter ranges with time in the detection range.

Analysis of chemical composition and change over time: Analyze the change of a certain chemical composition over time, according to its changing trend, it can accurately reflect the special changes that occur within a certain time; it is particularly important to realize real-time online analysis of heavy metals in particulate towels The current irreplaceable method.

Source analysis: According to the classification and time change of the particulate matter, determine its possible source.

Study on the evolution process and mechanism of particulate matter: According to the evolution trend of different particulate matter over time, infer the possible formation mechanism. ^[3]