Abstract
The kinetics of signal formation in collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) are discussed, and theoretical equations describing the relation between the concentration of the target molecule and the detected atomic absorption in case of pure and impure samples are derived. The validity of the equation for pure samples is studied experimentally by comparing measured target molecule concentrations to concentrations determined using two other independent techniques. Our study shows that CPFAAS is capable of measuring target molecule concentrations from parts per billion (ppb) to hundreds of parts per million (ppm) in microsecond timescale. Moreover, the possibility to extend the dynamic range to cover eight orders of magnitude with a proper selection of fragmentation light source is discussed. The maximum deviation between the CPFAAS technique and a reference measurement technique is found to be less than 5 %. In this study, potassium chloride vapor and atomic potassium are used as a target molecule and a probed atom, respectively.
Highlights
Photofragmentation and fragment detection (PF/FD) techniques improve selectivity and sensitivity in gas sensing [1]
The kinetics of signal formation in collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) are discussed, and theoretical equations describing the relation between the concentration of the target molecule and the detected atomic absorption in case of pure and impure samples are derived
Our study shows that CPFAAS is capable of measuring target molecule concentrations from parts per billion to hundreds of parts per million in microsecond timescale
Summary
Photofragmentation and fragment detection (PF/FD) techniques improve selectivity and sensitivity in gas sensing [1]. They are based on the fragmentation of the detected molecule and the sensing of the released fragment. Fragments are detected utilizing their emission [5–7] or absorption [8, 9] properties. A technique called collinear photofragmentation and atomic absorption spectroscopy (CPFAAS) was demonstrated in the detection of alkali chloride vapors [10]. The technique utilizes a UV laser pulse to dissociate alkali chloride molecules to alkali and chlorine atoms, and a narrow bandwidth laser diode to monitor the concentration of the alkali atom. The collinear alignment of the two beams through the sample volume enables the detection of temporally increased alkali atom concentration within the volume determined by the UV beam. The large absorption cross-sections and the narrow absorption profiles of the alkali atoms favor their detection, when interfering fragments, such as O2, exist
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