Small and Mighty

A “miniaturized” mass spectrometer promising higher resolution and more sophisticated detection is being developed by a team at Duke University, NC, USA. Jeffrey Glass, professor of electrical and computer engineering and lead researcher, has been working on the development of this high-resolution miniature mass spectrometer, and says that the benefits are likely to have a broad reach, from point-of-care applications to space travel. Here he tells us more about the development of coded aperture MS – and why this technology is welcome news.

How did you come to focus on the challenge of size and sensitivity versus resolution?

Miniaturization of a mass spectrometer is considered the “Holy Grail” of chemical sensing due to the broad range of chemicals it can detect and its sensitivity to low concentrations of those chemicals.  However, there is a historical trade-off between resolution and throughput when miniaturizing a spectrometer. In order to effectively miniaturize a mass spectrometer, we had to find a solution to this trade-off – hence the development of a coded aperture mass spectrometer.

How does a coded aperture mass spectrometer work?

In a typical sector mass spectrometer, the ions pass through a thin slit. The slit width interacts with the path length the ions take through the instrument to define the system resolution. When you shrink the instrument, you shrink this path length, and so the slit width has to shrink as well in order to maintain the system resolution. This means the throughput passing through the instrument is going to be reduced, decreasing signal intensity and reducing the signal-to-noise ratio (SNR). We got around this issue by using a “coded aperture” – an array of several slits arranged in a particular mathematical pattern. The resulting measurements do not directly resemble the spectrum, but we can use a reconstruction algorithm to undo the mixing introduced by the aperture and recover the spectrum. The net result is that we are able to achieve high-resolution while also maintaining SNR; this breaks the historical trade-off between resolution and throughput and frees us to miniaturize the system without sacrificing performance.

Is the coded aperture restricted to specific types of MS?

We are currently investigating the various types of MS that work with coded apertures. So far, we have shown that they work with simple magnetic sectors and more complex instruments that employ an electric sector and magnetic sector, like the Mattauch-Herzog geometry described in our recent publication (1). In practice, coded apertures allow for a smaller MS system by maintaining the throughput of the spectrometer without compromising the resolution.

How will the system compete against other portable technologies?

Our miniature mass spectrometer has several advantages. First, it is a spectrograph, meaning that it measures the entire spectrum at once; devices like the M908 are serial instruments that measure each mass sequentially. Measuring the entire spectrum all at once allows for more efficient sample use. In addition, due to the coded apertures, our ability to maintain throughput without sacrificing resolution will likely allow us to have a higher resolution instrument than other portable technologies.

What challenges lie ahead?

Although the fundamental proof of concept for coded aperture mass spectrometry has been achieved, there are several engineering challenges to be tackled ahead of making a working portable system. We must miniaturize all of the various components of the mass spectrometer including the ion source, sample inlet, detector, and vacuum pumps. In addition, one of main challenges of developing an instrument is to get all of the various parts working together at the same time!