Automated sample pretreatment technologies: from surface-based liquid microjunction sampling to flow-based platforms

Sample pretreatment plays a central role in analytical workflows, particularly for complex matrices where efficiency, reproducibility, and sustainability are essential. In recent years, increasing levels of automation have driven a gradual transition from labor-intensive manual procedures toward integrated and standardized pretreatment strategies. This review examines two representative automation paradigms that have significantly influenced recent developments in sample pretreatment: surface-based liquid microjunction sampling and flow-based automated platforms. Liquid microjunction techniques, including liquid extraction surface analysis, liquid microjunction surface sampling probe, and the MasSpec Pen, enable localized and minimally invasive extraction directly from solid or semi-solid substrates. These approaches have extended the applicability of mass spectrometry to in situ biological and clinical analysis, while also presenting challenges related to spatial resolution, extraction selectivity, and quantitative consistency. In contrast, flow-based platforms such as lab-in-syringe and online solid-phase extraction emphasize controlled fluid handling, process integration, and operational reproducibility, and have become important tools for high-throughput and trace-level analysis in biomedicine, food safety, and environmental monitoring. This review focuses on the methodological characteristics, design considerations, and practical limitations of these automation strategies, highlighting how platform architecture influences analytical performance and application scope. Current trends toward greater integration, intelligent control, and improved standardization are also discussed, with reference to future directions in automated analytical workflows.