Estimation of Rate Constants Using Statistical Moments of Spatially Resolved Signal Profiles for the Elucidation of Analyte Transformation Mechanisms in an Inductively Coupled Plasma

K. P. Li*, Tiing Yu, J. D. Hwang, K. S. Yeah, J. D. Winefordner

*Corresponding author for this work

Research output: Contribution to journalArticle

13 Scopus citations

Abstract

The height-resolved atomic and Ionic emission profiles of calcium and magnesium are characterized by their statistical moments. The zeroth and first moments are employed for estimating rate constants of atomization, kD, Ionization, kI, recombination, kR, and vapor plume expansion, kx. Because the Initial number density, n0, of the molecular analyte species In the vapor plume resulting from a single solution droplet Is not measurable, only k, can be estimated directly from the signal profiles. Rate constants kD and kR can be calculated by using an educated guess of kx, because kx can only vary within a narrow range. Comparison of experimental and simulated signal-height profiles showed the radio frequency (rf) power dependence of kx. As rf power Is Increased, kx decreases slightly, resulting In a significant Increase In kD. The power dependence of k, for Ca Is different than for Mg. The increase In k, with rf power shows that Ionization Is less favorable as a rate-determining step In Ca transformation excitation In high power. The k, for Mg Is nearly Independent of rf power. The Mg atomic and Ionic profiles vary with power In the same manner, whereas the Ca I profiles shift with power. Furthermore, the Mg II/Mg I intensity ratio at a given height Is essentially Invariant with solution concentration.

Original languageEnglish
Pages (from-to)1599-1605
Number of pages7
JournalAnalytical Chemistry
Volume60
Issue number15
DOIs
StatePublished - 1 Aug 1988

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