Estimating in-air micro-PIXE beam conditions from element concentrations in plant obtained by inductively coupled plasma mass spectrometry

Knowledge of elemental localization in plants is essential for understanding nutrients and toxic element transport. In-air micro–particle induced X-ray emission (micro-PIXE) enables multi-elemental mapping of living tissues by detecting characteristic X-rays from trace elements. Unlike electron beam–based methods, micro-PIXE is conducted in air and allows non-destructive analysis of living cells. However, optimizing beam exposure time in advance remains difficult and often increases analysis time. In this study, we estimated optimal observation conditions for in-air micro-PIXE using element concentrations measured by inductively coupled plasma mass spectrometry (ICP-MS). Lotus japonicus stems were cultured in solutions containing 0.01–100 mM Cs, Na, Fe, or Zn, and elemental distributions were analyzed by both methods. Fe, Zn, and Cs showed clear concentration-dependent distributions and were successfully mapped by micro-PIXE, whereas Na could not be mapped due to X-ray absorption by the beryllium window. X-ray detection counts showed strong correlations with ICP-MS values, enabling estimation of appropriate irradiation conditions. These results provide practical guidelines for predicting exposure time or element accumulation required for successful mapping, improving the efficiency and accessibility of micro-PIXE for plant element studies.