Can an online mass spectrometer perform mass spectrometry imaging directly?

Online mass spectrometers excel at real-time, high-frequency monitoring of continuous flows or dynamic processes; however, as they lack intrinsic spatial scanning capability, they cannot directly produce images of substance distribution. To obtain spatial imaging, it is necessary to combine them with an imaging ion source capable of point-by-point scanning (such as MSI DPI or LDPI), or to incorporate spatially resolved sampling into the continuous sampling process. The capabilities of the two are complementary: online mass spectrometers capture ‘time’, whilst imaging mass spectrometers capture ‘space’.

Online mass spectrometers (such as the Neo Source INSTRUMENT ProC series and the ProC-1S flue gas multi-component dynamic analysis system) are designed for reaction off-gases, flue gases and catalytic processes. They introduce gas or vapour into the ion source in real time to record changes in composition over time at a high sampling rate; the core principle is ‘time resolution’.

The key to imaging lies in possessing both “mass information” and “spatial coordinates” simultaneously. Online mass spectrometry only answers the questions “what is present at this moment” and “what is the concentration”, but does not record “which location on the sample it originates from”; consequently, a single online mass spectrometer cannot generate a spatial distribution map of molecules.

To combine these two aspects, one viable approach is to connect an imaging ion source to an online mass spectrometer: by having a DESI or laser probe scan the sample surface, triggering an online TOF acquisition at each position, thereby assembling an image from “point-by-point full spectra”. New Source’s MSI DPI / LDPI integrates imaging capabilities into host instruments, including the ProC series, to achieve the fusion of “online + imaging”.

Another approach is spatially encoded sampling. For example, in microfluidic or two-dimensional sampling arrays, different positions correspond to different sampling timings, and the online mass spectrometer then reconstructs the spatial distribution from the temporal data; however, this method has limited spatial resolution and is far less precise than dedicated imaging sources, making it suitable only for specific array samples.

Returning to the fundamental distinction: if a study is solely concerned with process dynamics (reaction kinetics, emission curves), online mass spectrometry is sufficient; if the focus is on ‘how substances are distributed on tissue or material surfaces’, an imaging source is essential. Treating online mass spectrometry as a substitute for an imager is incorrect; the correct understanding is that it involves ‘adding accessories and combining capabilities’.

Can the ProC-1S flue gas system be converted into an imager?

It cannot be directly converted into an imager, as it lacks a spatial scanning mechanism; however, its TOF main unit can be used as an analyser, with an external MSI DPI/LDPI imaging source connected to it, thereby providing imaging capability whilst retaining the original flue gas monitoring function.

Does the rapid sampling of online mass spectrometry aid imaging?

Yes, it does. For example, the ProC-2 has a sampling rate of 30,000 Hz, meaning that the full spectrum for each spatial point can be obtained in an extremely short time, directly reducing the total image acquisition time; this is a key advantage of using an online mass spectrometer for imaging.

Can ‘real-time dynamic’ imaging experiments be carried out?

Standard imaging involves static cross-sectional scanning; to achieve dynamic imaging, the sample state must remain unchanged or be subject to controlled changes (such as in an in-situ reaction cell) during acquisition, in conjunction with a high-speed imaging source. It is only in such cases that the high-frequency capabilities of online mass spectrometry come into their own.