Kinetic Contributions to Arsine Generation: Oxygen Effects and Qualitative Interpretation in FIAS Systems

Abstract

Experimental evidence demonstrates the coexistence of two distinct kinetic pathways in arsine generation, mediated by hydroborane-type intermediates and strongly modulated by the gaseous environment. Replacing hydrochloric acid with water as the carrier phase did not reduce sensitivity, confirming that the residual acidity of the sample is sufficient to activate the reaction.The introduction of air as carrier gas produced spectral profiles with two well-defined peaks, whose position and shape depend on oxygen flow and pumping rate. In contrast, argon as carrier gas yielded a single clean peak, confirming that oxygen selectively accelerates the oxidative cleavage of borane intermediates and modulates the temporal expression of the signal. Under air, the second peak shifted more rapidly to shorter times and maintained its absorbance, dominating the fused peak observed at high flows. During atomizer shutdown, the first peak decayed rapidly, while the second remained stable for several minutes, suggesting the formation of a more resistant species-possibly oxidized or surface-bound-that acts as an arsenic reservoir. The combination of temporal dynamics under air, differential stability during shutdown, and the modulatory effect of oxygen confirms the existence of two kinetically distinct pathways. The proposed mechanistic model integrates these findings and provides a coherent framework for interpreting hydride formation, transport, and atomization in coupled systems.