Mass spectrometry vapor detection makes airport security easier

At the airport, the technology used by the staff of the Transportation Security Administration (TSA) to scan and inspect your hands and laptops is a form of 'trace detection'-ion mobility spectroscopy (ion mobility spectroscopy). spectroscopy). Within a few seconds, the sample is first vaporized into chemical ions, and then the detector uses its molecular size and shape to identify whether it is an explosive, and if it is indeed an explosive, it will trigger an alarm.　　 But when there are many objects to be tested, this method becomes time-consuming and laborious, and its effectiveness largely depends on the sampling level of the staff. In addition, this technology also requires contact sampling, which means that security personnel have to touch the surface of objects that may contain residues. Therefore, this technique is useless when the criminals do not intend to pass the security check and their personal belongings have no chance to be searched.　　 Some security teams rely on trained dogs to use their sensitive sense of smell to sniff out explosives. But behind the routine deployment of detection dogs means extremely heavy logistical and training work. At the same time, the direct use of dog close-up detection may also make passengers with special cultural backgrounds disgusted.　　 Therefore, researchers have long been committed to developing a new type of chemical detection technology that can 'sniff' explosive vapors like dogs. However, many attempts over the years have failed due to insufficient sensitivity. In response to this problem, our research team has been engaged in research work for nearly 20 years and has made great progress.　　More and more sensitive　　 want to design a technology that can match the dog's nose, the biggest difficulty is that the saturated vapor pressure of most explosives is very, very low. The 'equilibrium vapor pressure' of a material is basically the content of the material in the air under ideal conditions at a specific temperature (that is, how much content can be detected).　　 The equilibrium vapor pressure of nitrogen-containing organic explosives (such as TNT, RDX and PETN) commonly used by military forces all over the world is only about one part per trillion. In other words, if you want to reliably sniff out the vapors of these explosives in an actual working environment (such as a crowded and busy boarding area in an airport), the sensitivity of the detector must reach one part per trillion (ppq) Level.　　 But this has exceeded the capability of trace detection equipment. You know, having a detection level of 325ppq is equivalent to being able to find a specific tree within the entire earth.　　 However, recent research has advanced the detection level to the range of one part per trillion. In 2008, an international team used an advanced ionization technique called secondary electrospray ionization mass spectrometry to achieve a detection level better than one part per trillion required to detect TNT and PETN.　　 In 2012, our research team at the Pacific Northwest National Laboratory (PNNL) used atmospheric flow tube mass spectrometry (AFT-MS) to successfully detect RDX steam with an equilibrium vapor pressure below 25ppq directly and in real time. The sensitivity of a mass spectrometer depends on how many target molecules can be ionized and transferred into the mass spectrometer for detection. The more fully carried out this process, the higher its sensitivity will be. The special feature of our AFT-MS design is that it uses time to maximize the probability of collisions between explosive vapor molecules and air ions generated by the ion source. It is the degree of reaction between these air ions and explosive molecules that determines the sensitivity. The use of AFT-MS allows us today to be able to detect a series of explosives whose equilibrium vapor pressure is lower than 10ppq. The perfect and simple schematic diagram of the AFT-MS device. Next step: Put it into practical use. Therefore, the explosive chemical detection instrument we have developed at present is no longer subject to contact sampling, but can 'sniff' out explosives like dogs. taste.　　 The instrument provides exciting new possibilities for safety inspections: first, it has the ability to detect explosive vapors similar to dogs, and second, it can work continuously and uninterrupted. Sampling for trace detection no longer requires direct contact with the suspicious object to be tested. And engineers can design a non-intrusive 'walk-through' explosive detection device, just like those common metal detectors.　　 The real innovation of this technology lies in its extremely high sensitivity, which allows it to directly detect the steam plume. Therefore, we no longer need to collect explosive particles and then vaporize them (for example, in the past trace detection technology, very noisy air nozzles were used to remove particles from people). Now, higher sensitivity means that we can continuously sample explosive molecules in the air as passengers pass by.　　 This technology will undoubtedly make airport security checks easier, and at the same time, it can greatly increase the throughput of security checkpoints and improve the experience of passengers. We can also place this type of device at the entrance of an airport terminal or other public facilities. Once the explosive enters the building, it can be detected immediately (instead of only detecting the explosive when it passes through the security checkpoint). Obviously Will greatly improve the safety of public places.　

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