High-Sensitivity and High-Speed Single-Particle Inductively Coupled Plasma Spectrometry with the Conical Torch

Significant advancement has been achieved in single-particle analysis with the new conical ICP torch in terms of sensitivity, precision, and throughput. Monodisperse desolvated particles of eight elements (Na, Al, Ag, Sr, Ca, Mg, Fe, and Be) were injected into the conical torch, and signal peak characteristics, precision, and kinetics of atomization and ionization were investigated with optical spectrometry. A particle introduction system was designed to ensure a smooth and uninterrupted delivery of desolvated particles to the plasma. The important finding is that, compared with the conventional Fassel torch, the conical torch offers a 1.5-8 times higher peak intensity, a 2-4 times higher peak area, a 2 times shorter peak width, and higher precision (i.e., a 1.5 times lower RSD for peak intensity and a 1.8 times lower RSD for peak width on average). Also, mass detection limits were found to be similar or up to 8 times lower (i.e., 2 times lower diameter detection limit) for the conical torch. The results indicate that these features are due to a much higher electron density, excitation temperature, and robustness which, together with an improved particle trajectory, lead to rapid vaporization/atomization/ionization of particles with minimized atom/ion cloud diffusion. Finally, the torch was demonstrated to be capable of analyzing single particles at a rate of at least 2000 particles per second with high sensitivity and precision. On the basis of these results, the conical torch is expected to bring about new possibilities in ICP-based single-particle analysis.