Points to Note Regarding the Installation and Modification of Mass Spectrometry Imaging Sources: Key Considerations for Vacuum Adaptation and Mode Switching

Fitting a mass spectrometry imaging source onto an existing main unit involves technical challenges not only in the source itself, but also in the details of the installation and modification. Inadequate vacuum adaptation can compromise the stability of the main unit, whilst unfamiliarity with mode switching can result in significant time wasted on debugging. This article lists the key points to note during installation and modification in sequence, for the reference of teams planning to carry out such installations.

Three pre-installation checks

Mechanical interfaces are the first hurdle. The desorption and ionisation zone of the imaging source must be precisely aligned with the host’s ion inlet; the dimensions of the interface flange and the height of the mounting base must be confirmed according to the host model. Vacuum ports are the second hurdle. Atmospheric-pressure sources (such as DESI/PI dual-mode) typically have little impact on the host’s vacuum, but if the imaging source itself involves local vacuum or pressure differential structures, the load margin of the host’s vacuum system must be calculated. Software protocols are the third step. Imaging scan control must be synchronised with the mass spectrometer’s acquisition triggering; mass spectrometers with closed protocols may be incompatible, so this must be confirmed in advance.

Vacuum adaptation: Modifications to ambient-pressure sources are minimal, but an assessment is still required

For ambient-pressure imaging sources such as DESI/PI, the working area is on the atmospheric side; ions enter the host’s vacuum chamber via a capillary or transfer tube, whilst the host’s own vacuum system operates largely as normal, meaning the scope of modification is relatively small. However, ‘relatively small’ does not mean ‘no assessment is required’. It is necessary to confirm that the insertion depth of the transfer tube and the impact of pressure differentials on the main instrument’s vacuum level remain within acceptable limits, and to verify that the vacuum remains stable during prolonged continuous imaging. For LDPI-type configurations, the compatibility of the laser path with the vacuum window must be confirmed based on the specific setup.

The prudent approach to vacuum compatibility is as follows: first, conduct a baseline vacuum test on the main instrument, recording the vacuum level and fluctuations during normal operation; after installing the imaging source, retest and compare the differences before and after installation. If the vacuum level deteriorates significantly, one should re-examine the interface seals and the installation of the transmission tube, rather than continuing to operate with a fault.

Mode switching: How to use the DESI/PI dual mode on the DPI

The DESI/PI dual mode on the MSI DPI means that a single source can switch between DESI single mode and DESI+PI dual mode. The switch essentially involves enabling or disabling the photochemical ionisation channel and adjusting the desorption-ionisation window accordingly. Two operational points require attention: firstly, recalibrate the spray and laser/light source parameters after switching, as ionisation enhancement alters the optimal operating point; secondly, record the mode combination corresponding to each sample to create a reproducible parameter template, thereby avoiding the need to start from scratch each time.

Post-installation validation procedure

Do not rush to analyse real samples. First, run through the entire workflow using standard samples (such as plant sections or quality control slides with known compositional distributions) to ensure: normal scan control triggering, stable pixel intensity and accurate spatial registration. Only proceed to research samples once validation has been successfully completed. The validation phase can uncover latent issues relating to interfaces, vacuum systems and software, which is far less costly than having to rectify problems retrospectively.

Personnel and Documentation

Installation and modification are not merely hardware engineering tasks; they also involve the handover of operational procedures. It is recommended to maintain three sets of documentation: records of interface and vacuum adaptation, parameter templates for mode switching, and a troubleshooting checklist. Only after operators have undergone training can they carry out routine maintenance and parameter adjustments independently, without relying on external support.

Summary

When installing and modifying mass spectrometry imaging sources, vacuum adaptation and mode switching are two key focal points. Whilst modifications to atmospheric-pressure sources are minimal, the vacuum load must still be assessed; for dual-mode sources, reproducible parameter templates must be established. Only by thoroughly implementing the three steps of verification, evaluation and validation can the stability of the installed system be guaranteed.