Pumping Ions – An Exercise in Engineering Sensitivity Into the Xevo TQ-XS Mass Spectrometer

Mark Roberts

Reading Time: 3 minutes

The challenge: Create the most sensitive mass spectrometer for quantitative analysis.

That’s a tall order for any design engineering team. When given that assignment for a next-generation, tandem quadrupole mass spectrometer, our design engineers first spoke to those for whom analytical sensitivity means the most: scientists doing quantitative studies for demanding clients relying on accurate and dependable results.

From those conversations our engineers came away with a clear mandate. They were told, “We need a mass spectrometer that will allow us to detect and measure more sample molecules than we can today and it would be great if we didn’t have to clean it as often as we do today.”

Waters design engineers began by thinking small – at the molecular ion level – and boiled down the options to a choice few.

  • Admit more ions from the source.
  • Improve the separation of them from neutral molecules and gases.
  • Concentrate and transmit the ions so more of them reach the detector and are available for analysis.
  • Treat fragile ions more gently.

Our engineers knew if they could accomplish these things, they’d be on the right path.

Fortunately we had the StepWave ion guide technology to work with. The StepWave ion guide was first introduced with the Waters Xevo TQ-S Mass Spectrometer.

StepWaveXS_ions and neutrals small
The StepWave XS Ion Guide pumps away gas, excess solvent and neutrals (blue) to waste while extracting ions (yellow) and transporting them to the mass analyzer in the Xevo TQ-XS System.

Its first-of-its-kind, off-axis design employs “travelling waves” to move ions from the source to the mass analyzer. The ion guide’s unique geometric design – conjoined upper and lower channels – guides the diffuse ion cloud into the lower channel.  As the charged molecular species are drawn up and into the smaller channel, contaminants such as gases, excess solvent and neutral species, continue straight through the large channel and exit the instrument via an exhaust port.

This has two effects:

  1. Capture as many ions as possible;
  2. Keep critical apertures and surfaces along the transmission path to the detector cleaner so that thousands of samples can be run without an appreciable loss in performance.

But Waters design engineers didn’t stop there. They enlarged the source aperture of the mass spectrometer to capture more sample ions, fine-tuned the ion guide’s voltage control to keep intact small, fragile molecules like amphetamines, endogenous steroids, vitamin D and pesticides, and they added a secondary segmented quadrupole ion guide to focus the ion beam even further and transmit more of the ions to the mass analyzer, thereby improving sensitivity dramatically. The result is the most sensitive tandem quadrupole mass spectrometer on the market for quantifying sample analytes over six orders of dynamic range.

For laboratories doing quantitative studies, a new day is here. They can meet tighter regulations around allowable levels of pesticide residues in food; perform biomarker studies and measure lower levels of endogenous molecules; and conduct DMPK studies of more potent drug compounds.

When it comes to pumping ions, Waters design engineers leave the heavy lifting to the new StepWave XS Ion Guide.

When it comes to quantitative sensitivity, the state-of-the art is the Waters Xevo TQ-XS Mass Spectrometer.

 

 

Related reading: