The effects of oxygen on the detection of mercury using laser-induced breakdown spectroscopy

A systematic study of the processes associated with mercury atomic emission in a laser-induced plasma and the interactions of mercury with oxygen spec ies is presented. At early plasma decay times, on the order of 5-10 mus, no significant variation in mercury atomic emission was observed with the add ition of oxygen-containing species. At intermediate and long decay times (1 0-100 mus), a significant reduction in the 253.7-nm mercury emission intens ity was recorded with the introduction of oxygen-containing species. The de crease in mercury emission was temporally coincident with the recombination of atomic oxygen, as measured by the O(I) emission. The decreased mercury emission was not due to thermal effects, based on plasma temperature measur ements, and was independent of the molecular source of oxygen, for similar concentrations of oxygen as air, carbon dioxide, and carbon monoxide. Analy sis of additional mercury atomic emission lines revealed that the reduction in mercury emission in the presence of oxygen species is limited primarily to the 253.7-nm transition. In concert, the data lead to the conclusion th at the 253.7-nm mercury emission line is selectively quenched by oxygen spe cies, primarily O-2 and NO, that are formed during the plasma recombination process. Implications for laser-induced breakdown spectroscopy-based emiss ions monitoring of mercury species are discussed. (C) 2001 Elsevier Science B.V. All rights reserved.