Ion mobility spectrometry (IMS) is an analytical technique that separates ionized molecules in the gas phase based on their mobility in a carrier buffer gas. Ions’ mobility depends on their averaged collision cross-sections (related to size, shape, and charge) and the pressure, temperature, and composition of the buffer gas.
There are several common variants of ion mobility spectrometers, including drift time IMS, traveling wave IMS, trapped IMS, high-field asymmetric waveform IMS, and differential IMS.
Drift tube IMS measures the time required for a given ion to transverse a given length under the influence of a uniform electric field. In specific time intervals, ions of a sample are allowed to enter the drift region by passing through a gate. The gating is usually accomplished by changing the electric potential of a shutter grid. Upon entering the drift region, ions are dragged through a buffer gas by a uniform electric field with a constant speed that depends on the mobility of the ions. Ions that pass the drift region are collected by a detector (typically a Faraday plate) in the order from the fastest to the slowest. The ion current is amplified, converted to voltage, and then digitized to produce a plot of ion current vs. time (an ion mobility spectrum).
Applications of IMS
Ion mobility spectrometry (IMS) is widely used in a variety of applications, including explosives and drug detection, environmental analysis, and food safety testing. IMS holds several advantages as a method for detecting explosives, even when present in the presence of other compounds. Its sensitivity, speed, and portability make it particularly useful for applications in the field, such as airports and border crossings, where explosives detection is critical.
Furthermore, IMS can be used to detect trace amounts of illicit drugs, such as cocaine and methamphetamine, in a variety of sample matrices, including bodily fluids, surfaces, and packaging materials. It can also be used to detect prescription drugs in cases of drug abuse or overdose. IMS is also used in environmental analysis to detect and quantify trace levels of pollutants in air, water, and soil samples. It is particularly useful for detecting volatile organic compounds (VOCs), which are gases emitted by a wide range of products and processes.
In the food industry, IMS is used to detect contaminants and pathogens in food products and to ensure quality control and compliance with food safety regulations. It can be used to detect contaminants such as pesticides, mycotoxins, and heavy metals in a variety of food products, including fruits, vegetables, grains, and meat. IMS is also used in a variety of other applications, including the detection of hazardous chemicals, the analysis of petrochemical products, and the identification of unknown compounds. Overall, IMS is a versatile and sensitive analytical technique that is widely used in a variety of fields for the detection and identification of ions.