Ion Mobility Spectrometry

What is Ion Mobility Spectrometry (IMS) ?

Ion Mobility Spectrometry (IMS) is an analytical technique that separates ions based on their movement through a gas under the influence of an electric field. The technique is particularly useful in separating ions that are similar in mass but differ in shape or size. By coupling IMS with mass spectrometry (IMS-MS), scientists can achieve an additional level of separation, which enhances the ability to identify and analyze complex mixtures of molecules, such as proteins, metabolites, and lipids. IMS operates on a very fast timescale, making it a valuable tool in various scientific workflows.

Different Types of IMS

There are several types of IMS, each with unique characteristics and applications:

• Drift Tube Ion Mobility Spectrometry (DTIMS): The most traditional form of IMS, where ions move through a gas-filled tube under a uniform electric field. DTIMS is known for its ability to measure ion mobility directly and calculate collision cross-section (CCS) values, providing insight into the shape and size of ions.

• Traveling Wave Ion Mobility Spectrometry (TWIMS): In this method, ions are propelled through the drift region by oscillating electric fields, creating waves that push the ions forward. TWIMS is particularly advantageous for its lower voltage requirements and its ability to enhance separation by increasing the path length ions travel.

• Trapped Ion Mobility Spectrometry (TIMS): TIMS traps ions in an electric field and then releases them based on their mobility. This method allows for highly selective separations and can be tuned for different experimental needs. It is also compact, making it suitable for integration into smaller instruments.

• Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS): FAIMS uses alternating electric fields to separate ions based on their mobility differences at high and low electric fields. This method is often used as a filter to reduce background noise and improve the detection of target ions.

• Differential Mobility Analyzer (DMA): DMA operates at ambient pressure and is typically used for measuring large molecules, such as proteins and viruses, by scanning ions and detecting their mobility directly.

Applications of IMS-MS

IMS-MS is a powerful tool with diverse applications:

• Isomer Separation: IMS can distinguish between isomers, which are molecules with the same formula but different structures. This is particularly useful in analyzing lipids, carbohydrates, and proteins, where structural differences are crucial.

• Signal Filtering: IMS-MS can filter out background noise, making it easier to detect specific ions in complex mixtures. This is especially beneficial in environmental analysis and when analyzing samples with many contaminants.

• Untargeted Metabolomics: In metabolomics, IMS-MS helps identify unknown metabolites by adding mobility information to the mass spectrometry data, increasing confidence in the identification of compounds.

• Structural Biology: IMS-MS is used to study the structure of biomolecules, such as proteins and nucleic acids, providing insights into their function and interactions.