A modern twist on an old technology could soon help detect rogue methane leaks, hidden explosives and much more. A Duke University team is using software to dramatically improve the performance of chemical-sniffing mass spectrometers.
Conventional mass spectrometers separate compounds by giving them an electric charge and passing them through electric and/or magnetic fields. The lighter the compound, the more it bends in the field. By determining what compounds make up a given sample, these instruments can identify almost any substance.
Mass spectrometers were invented in the 1930s, and they're still typically the size of an oven or refrigerator. Inherent hurdles to miniaturization have made it difficult to use them outside of a laboratory. But with the help of modern data analytics, researchers at Duke have demonstrated a technology using a so-called "coded aperture" that promises to shrink these devices while maintaining their performance. The advance could lead to portable mass spectrometers that could be used to detect environmental or safety hazards in the field.
"In a typical mass spectrometer, the charged molecules pass through a thin slit, which defines your resolution," said Jeff Glass, professor of electrical and computer engineering at Duke and principal investigator for the project. "When you try to shrink the instrument, you have to shrink the slit too. That means the number of ions (charged molecules) passing through is going to drop and you're going to lose signal intensity. We got around this issue by using a several slits, which code the ions."
Glass likens the new technology to watching a solar eclipse in grade school. Students often poke a small hole in a piece of cardboard, which acts like a lens to create an image of the eclipse on the ground. And as anyone who has ever done this knows, the smaller the hole, the better the detail of the eclipse. But a smaller hole also makes it dimmer and harder to see. This is exactly the challenge faced when scaling down a mass spectrometer.
The solution, Glass says, is to make many tiny pinholes to create an array of eclipses, and then to use a computer to reconstruct them into a single image. This way you get the sharpness of the tiny pinhole with the brightness of a large pinhole. The key is in knowing the pattern – or code – of the array of apertures. Thus the name of the technology, coded aperture.
The researchers have demonstrated that their coded aperture works in a newer, more complex type of mass spectrometer created to help make the devices smaller, though not nearly as small or precise as coded apertures could make them. Their work now is focusing on trying coded apertures in different versions of mass spectrometers to determine which would be best for creating scaled down, mobile devices for field use. They are also working to show these devices can detect trace amounts of methane to spot leaks in infrastructure and various explosives to thwart terror attempts.