Advancing LA-ICP-TOF-MS multi-elemental mapping: The bidirectional scanning approach

The rapid development of laser ablation-ICP-mass spectrometry (LA-ICP-MS), particularly through the introduction of low-dispersion ablation cell designs and improved aerosol transport systems, has substantially increased achievable pixel acquisition rates for elemental mapping applications. However, conventional unidirectional scanning restricts the effective pixel acquisition rate and consequently limits overall sample throughput as switching from one scan line to the next introduces additional waiting time. A bidirectional scanning approach, in which pixel data would be collected in alternating opposite scanning directions, could mitigate this issue and reduce analysis time substantially.

In this study, a systematic evaluation of bidirectional scanning and its analytical implications is presented. A 193 nm ArF*excimer-based kHz LA-unit equipped with an ultrafast tube-type ablation cell was coupled to an ICP time-of-flight-MS (ICP-TOF-MS) unit to investigate single-pulse response (SPR) profiles for different scan directions. Upon optimization of all LA parameters, no significant differences in SPR characteristics were observed between the forward and reverse scanning direction in both horizontal and vertical scanning mode. Additionally, different approaches were evaluated for their effectiveness in reducing peak tailing associated with non-symmetric SPR profiles. As a proof-of-concept, bidirectional scanning for elemental mapping was demonstrated through multi-element imaging of a highly primitive chondritic meteorite and a mouse spleen tissue section. The resulting maps reveal finely resolved image features for both single and multiple dosage approaches, while achieving a two-fold improvement in effective pixel acquisition rate (635 pixels s^-1) relative to the traditional unidirectional scanning approach.

Introduction of a bidirectional scanning approach was proven as an effective strategy for improving the effective pixel acquisition rate and therefore, substantially reducing analysis time and enhancing sample throughput in multi-elemental mapping via LA-ICP-TOF-MS. This was achieved while maintaining high image quality and fidelity, as confirmed by multiple quantitative image metrics.