What are the strengths of dual-field reflection time-of-flight mass spectrometers in imaging?

The dual-field reflection (Wiley-McLaren) TOF uses two accelerating electric fields and reflectors to correct for the initial energy and spatial dispersion of ions, thereby enhancing mass resolution whilst maintaining a wide mass range and high ion transfer efficiency. For imaging applications, this enables each spatial point to obtain a full spectrum that is ‘well-resolved, rapidly acquired and broadly covered’, making it a key design that balances resolution and throughput.

Single-field TOF systems have limitations. When ions are launched in the same pulse, there are still minute differences in their initial energy and spatial position; these differences translate into variations in arrival time, thereby limiting resolution. Single-field linear TOF systems have limited ability to correct for this, making it difficult to achieve high resolution.

How does the dual-field reflective design overcome this challenge? The Wiley-McLaren configuration utilises two accelerating electric fields of differing intensities, causing ions to be ‘pre-dispersed’ during the launch phase into a state where they can be re-converged according to energy; mirrors are then used to make slower ions travel a longer distance and faster ions a shorter distance, ensuring they ultimately arrive at the detector simultaneously. This cancels out the energy dispersion, thereby enhancing resolution.

The primary benefit for imaging is the ability to ‘separate’ peaks. Higher resolution means that adjacent m/z peaks can be distinguished, reducing co-elution interference and resulting in a cleaner spectrum at each point. The New Source ProC-2 achieves a resolution of >2000 at m/z=92, which is sufficient to separate many metabolites and lipid peaks with closely spaced masses.

The second benefit is ‘fast acquisition and wide coverage’. The dual-field design enhances resolution without compromising ion transmission efficiency, ensuring that ions across a wide mass range reach the detector efficiently; combined with a high sampling rate (up to 30,000 Hz on the ProC-2), the full spectrum is rapidly acquired at each spatial point, supporting the throughput requirements of large-area imaging.

Imaging must be both fast and accurate; the dual-field reflective TOF strikes a balance within the ‘resolution–speed–mass range’ trade-off, unlike certain high-resolution analysers that achieve this at the expense of long integration times. This is precisely why New Ceyuan has incorporated it into the MSI series of imaging main units.

Is a dual-field reflective TOF significantly more expensive than a single-field one?

The mirrors and dual-stage electric field structure increase design and assembly complexity, so the cost is typically higher than that of a single-field linear TOF; however, in imaging applications, this trade-off delivers both resolution and throughput, and the improvement in output quality often outweighs the price difference.

Does the reflective design affect ion transmission efficiency?

A well-designed reflective TOF achieves transmission efficiency close to that of a linear design. Xinceyuan’s dual-field solution maintains high-efficiency transmission across a wide mass range whilst improving resolution, without sacrificing ion count.

Is the dual-field reflective design used solely for imaging?

No. It is equally suitable for online, routine high-throughput TOF analysis; Xinceyuan utilises it on the ProC series online mass spectrometer, a shared host platform for both mass spectrometry and MSI imaging sources, enabling a single analyser to serve multiple purposes.