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What Is IMS

Posted on September 29, 2022 by Zeng YingLab Equipment

What is IMS?

IMS, short for ion mobility spectroscopy, is a detection technique developed in the late 1960s that uses the difference in ion mobility time for the separation and characterization of ions, with the help of a concept similar to chromatographic retention time, and was initially called plasma chromatography.

Brief history of IMS development

IMS-ion-mobility-spectrometry
IMS-ion-mobility-spectrometry

Brief history of the development of Conventional IMS

In the 1970s: Ion mobility spectrometry emerged as a separation technique "comparable to gas chromatography in terms of separation efficiency", which was then called plasma chromatography; ion mobility spectrometry was cost-effective and fast, and was mainly used in the field of gas measurement at that time.

As a mass spectrometry technique that does not require a vacuum, it has been studied extensively. Since ion mobility spectrometry does not require an expensive vacuum system, the mass number of the measured material can be estimated based on the relationship between mass number and molecular size; and the price of mass spectrometry was very high at that time, so ion mobility spectrometry was used as vacuum-free, low-cost mass spectrometry. However, during the same period, the resolution of chromatographic techniques increased dramatically, and ion mobility spectrometry was left far behind in separation applications.

The 1980s: Ion Mobility Spectrometer (IMS) was used as a detector for chromatographs. Due to its portability, robustness, and suitability for field detection, the Ion Mobility Spectrometer is used in the military industry, detection of chemical weapons, and other fields.

From the 1990s to the beginning of the 21st century: ion mobility spectrometry was used in the field of detection of marijuana, drugs and explosives, especially after the "9/11" incident, explosives detection has become more important, and the demand for ion mobility spectrometry has increased. Currently, more than 200,000 units of this ion mobility spectrometry instrument have been sold worldwide for rapid detection in the field.

Also, ion mobility spectrometry can be added to the front end of existing mass spectrometers to add a dimension of separation, such as Waters' Synapt MS, Thermo Scientific's FAIMS, and AB SCIEX's SelexION, all of which are applications of ion mobility spectrometry.

All of the above ion mobility spectrometry instruments, however, have relatively low separation efficiencies and perform similarly to conventional ion mobility spectrometry.

Birth of High-Performance Ion Mobility Spectroscopy (HPIMS)

The concept of HPIMS High-Performance Ion Mobility Spectrometry Excellims was proposed to improve in terms of resolution (separation capacity), sensitivity, pre-treatment methods, linear range, and precision. Its structure can be considered as an improvement of DTIMS with a resolution of about 70.

Comparison of conventional IMS and HPIMS

Ion-mobility-spectrometry
Ion-mobility-spectrometry

Compared with conventional ion mobility spectroscopy, high-performance ion mobility spectroscopy has improved in terms of resolution (separation capacity), sensitivity, pre-treatment methods, linear range, and precision.

 Conventional IMSHPIMS
Resolution (separation capacity)12-4060-90
Sensitivity (minimum detection limit)pg-ng levelpg-ng level
Sampling and ionization methodSolid samples using thermal resolution, Ni63 radioactive ion sourceSolid samples are thermally resolved with a corona discharge source; liquid samples are electrosprayed; gas samples can also be fed directly
Analysis speed5-10 seconds5-10 seconds
Linear range1-2 orders of magnitude2-4 orders of magnitude
Precision10-15% RSD1-5% RSD

Application of IMS

IMS is a simple and reliable field analytical instrument with highly sensitive detection technology for applications in the following fields.

Military Applications

The modern analytical instrument ion mobility spectrometer is the first thing that comes to mind for military applications to detect chemical warfare agents. The ion mobility spectrometer is a simple and reliable field analyzer that can simultaneously monitor positive and negative ions, thus allowing simultaneous monitoring of a wide range of chemical warfare agents such as nerve agents, vesicant agents, blood agents, and asphyxiation agents, which is the reason for the rapid development of IMS technology. Because the drift tube can maintain constant temperature and low humidity conditions, the ion mobility spectrometer is very suitable for equipping naval and land forces for chemical defense, especially for the high temperature and high humidity environment in which naval ship units are located.

National safety department

Since IMS is a highly sensitive detection technology at the molecular level, the corresponding instruments have extremely low detection limits and can detect particulate objects in trace quantities with the addition of a vacuum injection system. IMS can detect explosives in letters, packages, and pads of different shapes and sizes within seconds, and can also be used for the detection of human carry-ons. National security departments at all levels can use IMS's highly sensitive detection technology to detect explosives to ensure the safety of the country and people's lives.

Customs departments

Customs departments are increasingly using IMS monitoring instruments to monitor contraband drugs such as dugs and narcotics. Thanks to the advanced detection technology of IMS, the monitoring of cargos and parcels at important gates such as customs and airports has been greatly enhanced, and the implementation of criminal activities such as smuggling and drug trafficking has been strongly combated.

Environmental monitoring

In recent years, IMS monitors have been used to monitor the environment, fires, water contamination, food and toxic gases in chemical plants, etc. IMS can also detect wood, which can be difficult to distinguish when barked woods are mixed together, but can be easily distinguished using the gases emitted by different woods using IMS. The built-in database can be modified from the chemical agent monitor to meet the needs of special environmental monitoring.

Other areas

With the proliferation of international terrorism, nuclear, biological, and chemical warfare agents pose a growing threat to world peace and the environment, as well as to the safety of people's lives. Detection systems to identify these dangerous bacteria, viruses and pathogens must be fast and accurate to enable people to respond quickly and take appropriate life-saving measures in a short period, thereby protecting lives.

How does IMS work?

IMS-spectrometry
IMS-spectrometry

The basic principle of ion mobility spectrometry is that when the ion source converts the sample into ions, driven by the electric field, these ions enter the weak electric field drift region through an ion gate that opens periodically. In the process of continuous collision with the counter-current neutral drift gas molecules, due to the different migration rates of these ions in the electric field, different ions are separated and successively reach the detector (Ion detector) to be detected. The mobility of the ions can be calculated from the drift time used by the ions (mobility is defined as the drift speed of the ions per unit electric field strength). Since the mobility of ions of various substances varies under certain conditions, the drift time of different ions through the electric field also varies. Therefore, the sample can be separated and characterized based on the measurement of the drift time, and the number of ions detected by the ion detector can be recorded for quantitative purposes. The ion mobility spectrometry technique is somewhat similar to the time-of-flight mass spectrometry technique, however, time-of-flight mass spectrometry must operate under high vacuum, whereas ion mobility spectrometry operates under atmospheric pressure.

Types of IMS

Drift-time ionmobility spectrometry, DTIMS

Aspiration ion mobility spectrometry, AIMS

Travelling wave ion mobility spectrometry,TWIMS

Field asymmetric ionmobility spectrometry, FAIMS

Trapped Ion Mobility Spectrometry, TIMS

Factors of IMS failure

IMS produces ion migration because when there is a DC electric field between the metals at the two ends of the insulator, the metals on these two sides become two electrodes, where the side that acts as the anode ionizes and migrates through the insulator to the metal on the other side (cathode) under the action of the electric field. Thus, the insulator is in an ionic conducting state. Obviously, this will make the insulator's insulation performance is reduced or even become a conductor and cause a short-circuit fault.

This occurs when there is a potential for electrolyte formation on the surface or inside the insulator of an IMS device in a humid environment. These include the type of insulator itself, composition, additives, fiber properties, resin properties, etc.

In terms of the composition factors of the substrate, there are three aspects.

One is the resin side, the composition of the resin, functional groups, the degree of curing , ion concentration (impurities, hydrolysis properties, etc.), moisture absorption.

Second, the fiber side: the density of glass fibers, organic fiber moisture absorption.

Third, the processing conditions: the conditions of the through-hole (with or without plating solution residue), lamination conditions (inter-resin adhesion), processing process residues (residues of roughening, plating, etc.).

In terms of the causative factors on the surface of the circuit board, there are more factors. In addition to the substrate factor, there are also electrolytes left in the plating holes by the components and metal components installed on the substrate that cannot be washed away, solder, glue, substances prone to electrolysis, dust plasma contamination, dew, etc.

From a more in-depth study, the design of the circuit and structure is also linked to the occurrence of ion migration failure. Because the electric field distribution on the circuit board and the polarity of the electricity carried by the oxidation-prone metal materials are related to the design of the circuit and structure. Among the line spacing and the line between the DC electric field and the occurrence of ion migration has a direct relationship, when the two adjacent lines between the DC electric field exists, including the existence of potential differences between the same phase current, in humid conditions, is very easy to occur in the anode state of the metal ionization and migration to the relative cathode. This is also related to the physical properties of the metal materials used for the components and devices installed in the line. For example, the ionization energy of the metal, the hydrolysis of the ions and the mobility of the ions have a great influence on the occurrence of ion migration.

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