How Does AMS Work?

Here’s how molecules are detected inside the AMS: Molecules in a gas sample enter the vacuum chamber and pass through an integrated ion source, which bombards the molecules with a stream of electrons to create positively charged ions. Then the ions travel through a miniaturized quadrupole mass filter, which separates the ions according to their mass to charge ratio (m/z). Finally, the ions reach a Faraday cup detector, which detects and quantifies them by m/z.

One of the components of the AMS Smart Spectrometer that is key to its small form factor – about the size of a toaster oven – is the miniaturized quadrupole array filter. This is an array of 16 cylindrical micro-rods, which generates 9 quadrupoles in the spaces bounded by four rods.

AMS Quadrupole Mass Spectrometer

16 poles (grey) result in 9 interspatial quadrupoles. Each pole radius = 500µm.

Other Quadrupole Mass Spectrometers

4 poles (grey) result in 1 interspatial quadrupoles. Each pole radius = 6000µm.

Above: Miniaturized quadrupole arrays contain smaller rods, and more quadrupoles, than a conventional quadrupole detector.

To filter ions by mass, the system applies combinations of direct current voltage and radio frequency voltage on rods opposite each other across the width of a quadrupole. This combination of energy can be tuned so that ions of particular m/z oscillate through the quadrupole, while others crash into the rods and disappear. The oscillations make the ions travel a path longer than the length of the miniaturized quadrupole rods. This means that the system can operate at higher pressure (mtorr) than conventional quadrupole systems.

Higher pressure operation also means a miniaturized mass spectrometer can have components that give it advantages for gas detection compared to typical residual gas analyzers. The higher pressure operation of the AMS Smart Spectrometer enables the vacuum pumps to be integrated inside the unit, rather than being external devices as with residual gas analyzers. It also generates a higher ion current, which allows the Smart Spectrometer to have a rugged and stable Faraday Cup ion detector sensitive to ppm concentrations across more than 6 decades of dynamic range. Residual gas analyzers, on the other hand, need an electron multiplier detector, which is inherently less stable, to amplify and detect low ion currents from low gas concentrations.

As the Faraday Cup detector detects ions inside the AMS, the system processes the signal into a mass spectrum. Proprietary algorithms then accurately calculate the mole fractions of each gas component with an accuracy of less than 1%. The results appear in real-time in a browser-based software controller, which can be accessed via remote log-in using a mobile device. The control software offers advanced features to support routine operation, and also offers skilled users to customize some capabilities.

The AMS Smart SpectrometerTM is calibrated using the gold standard Capacitance Diaphragm Gauge.