Week 2: The IMS That Cried Wolf

Hi everyone and welcome back to my blog!

My second week at MITRE seemed to mark the return(hopefully!) of warmer weather with Tuesday being in the 70s! Daylight savings switched over the weekend too, which was a bit of a struggle to adjust to, but nothing that a little trip to the coffee shop in MITRE 4 couldn’t fix!

As for my actual work, during my internship at MITRE, we will be focusing on different analytical tools used for chemical detection of trace substances in mixtures. The star of this past week has been a device called the Ion Mobility Spectrometer or IMS for short, which basically works by separating the different ions in a mixture based on their mobility through a ‘buffer gas’ in response to an electric field.

For those of you that are frequent flyers, the IMS is actually used for trace detection of controlled substances at airports!

The first step an IMS takes once it gets a sample is to ionize the molecules. This can happen in a lot of different ways depending on the sample’s state. A common technique includes electrospray ionization (which was used in an IMS study I read(Fernandez, 2009)). Once the molecules are ionized, an electric field pulls them through a drift region (filled with the buffer gas). The different types of ions in the mixture will travel through the drift region at different speeds. The IMS typically measures a variable known as drift time(dt) which measures how much time each ion took to travel through the drift region. The device will return certain peaks (that represent the drift times it recorded) and based on those different peaks, scientists should be able to identify which substances were in the mixture. If you’re interested in learning more about how the IMS works, you can check out this link: Ion Mobility Spectrometry: Fundamental Concepts, Instrumentation, Applications, and the Road Ahead – PMC

I got a chance to see an IMS in action this week as Casey and Nate(the lead and co-lead of the project I’m interning for) played around with it to see how it reacts to different compounds and mixtures. The IMS came with different traps (rough pieces of paper like material that you insert into the IMS for it to read). Before starting to sample, we had to enter a calibration trap (which was a strip with a certain calibrant on it) and a verification trap. Once that was set, we were ready to start testing with samples! Casey and Nate put tiny amounts (and I mean super tiny-like maybe half a milligram!!) of powder on glass slides and gently brushed a sampling trap across it. Sometimes, the trap would have such a tiny amount of powder on it that it wouldn’t even be visible! They fed the sample trap to the IMS and within a few seconds it would give us the peak readings. The IMS is super sensitive (which is how it’s able to process such tiny amounts of a sample), so they had to be extra careful to prevent any kind of contamination!

The specific IMS we were working with has a built-in detection system for certain controlled substances, so if it detects a peak that’s close enough to the peak of any of the substances in its system, it should play an alarm indicating that the sample contains controlled substances. One thing we learned early on is that even if the sample doesn’t contain any controlled substances, there’s a chance that the IMS will detect one anyways-kind of like crying wolf! This probably happened because the drift times of the substances we were testing ended up being uncomfortably close to the drift times of the substances it’s trained to detect.

Other studies that have worked with the IMS, specifically the Pacific Northwest National Library’s Performance Assessment of Field Portable Instruments and Assays for Fentanyl and Fentanyl Related Compounds (Bradley 2023), have found similar issues with the IMS being prone to false positives, and we definitely got to see just how true that is! This trait does makes me wonder how they deal with the false positives issue during airport scanning. In addition to the false positives, we also noticed that the IMS may potentially have an issue with consistency in its readings for the same sample. These are definitely important things to consider when assessing the IMS’ feasibility for on field trace detection of drugs.

Looking forward to next week, I finally completed my lab training so hopefully I’ll be able to do some hands-on work in the lab! I’ve learned a lot about lab procedures by watching Casey and Nate work this past week and I’m excited to put what I’ve learned to use!

Until next time,

Natasha

References:

Bradley, A., Mo, K. F., Melville, A., Sanders, D., Jensen, S., Lin, V., Mobberley, J., Doll, C., Orton, D., Heredia-Langner, A., & Ozanich, R. (2023). Performance Assessment of Field Portable Instruments and Assays for Fentanyl and Fentanyl Related Compounds. Pacific Northwest National Library. 20240105_FeRS-Final-Report_CLEARED Public Release

Fernandez-Maestre, R., & Hill, H. H., Jr (2009). Ion Mobility Spectrometry for the Rapid Analysis of Over-the-Counter Drugs and Beverages. International Journal for Ion Mobility Spectrometry. https://doi.org/10.1007/s12127-009-0025-x