Magnetic Sector Pre-Cell Mass Filters: The Cure for Garbage In, Garbage Out

“Garbage in, garbage out.” It’s the computer science concept that if you input nonsense data to a system/computer, then what you get is nonsense output. The same concept applies to collision reaction cells in mass spectrometry.

Collision cells are useful tools for allowing us to separate out the isotope/element of interest from isobaric interferences. However, they work because we can control the reaction chemistry in the cell. In other words, we know what we put in and what reactions are occurring.

Thermo Fisher Scientific: Magnetic Sector Pre-Cell Mass Filters: The Cure for Garbage In, Garbage Out

But let’s take sample input from a laser … Suddenly there are loads of trace and matrix elements swirling around in the plasma and the reaction chemistry gets messy. Ultimately, that means that the output from the collision cell is nonsense. Garbage in, garbage out.

Pre-cell mass filters are used to remove a lot of the nonsense going in. By allowing only a specific mass window to enter the cell, the reaction chemistry becomes much more predictable.

But there are pre-cell mass filters and then there are pre-cell mass filters. Traditionally, pre-cell mass filters have been based on quadrupole technology (think Thermo Scientific iCAP TQ or Thermo Scientific Proteus MC-ICP-MS). However, these quadrupole-based pre-cell mass filters have shortcomings in terms of precision and accuracy when you are interested in high-precision isotope ratios. In terms of accuracy, they suffer from the issue of non-exponential mass bias, which fluctuates wildly between analytical sessions, and when we try to use an exponential law correction, our isotope ratios are off by 1000s of ppm. In terms of precision, quadrupole-based pre-cell mass filters are lower energy, so they extract fewer ions — resulting in decreases of sensitivity of 25-50 percent.

Magnetic sector pre-cell mass filters do not suffer from these problems. They have stable exponential mass bias, producing accurate isotope ratios. The high ion extraction coupled with a reduction of space-charge effects (from filtering matrix elements) actually increases sensitivity by up to 25 percent, meaning even better precision.

The Thermo Scientific Neoma MS/MS MC-ICP-MS utilizes this patented magnetic sector pre-cell mass filter, guaranteeing you the best accuracy and precision for your isotopic analysis. To find out more, visit www.thermofisher.com/ms-ms. 

For a summary of this blog post, see our infographic.