Br isotope determination via the monitoring of CaBr transitions using high-resolution continuum source graphite furnace molecular absorption spectrometry. Potential for direct determination of Br in solid samples using isotope dilution

Abstract

This work investigates the possibility of obtaining Br isotopic information by generating a gaseous diatomic molecule in a graphite furnace and monitoring its absorption spectrum using a high-resolution continuum source device (HR CS GFMAS). Different metals (Al, Ba, and Ca) were investigated to produce this diatomic molecule and the most promising results, both in terms of isotopic shift and sensitivity, were obtained with Ca, thus leaving CaBr as the target species. The results demonstrate that, unlike what occurs when monitoring atomic spectra, which are characterized by very small isotopic shifts that can hardly be detected, using HR CS GFMAS it is feasible to observe several molecular transitions corresponding to Ca⁷⁹Br and Ca⁸¹Br that are spectrally resolved (i.e. they act like two different molecules absorbing at different wavelengths), and can be simultaneously quantified. The method developed relies on the addition of both Pd and Ca (as a chemical modifier and molecule forming agent, respectively), the selection of peak height values and the use of IBC-m (iterative baseline correction for the monitoring of molecules) for setting the baseline. This method enables accurate Br isotopic analysis in 10 mg L⁻¹ solutions with precision values around 2.5% RSD, without requiring any method for mass bias correction. Moreover, it is also demonstrated how the use of isotope dilution for calibration can help in circumventing severe chemical interferences (e.g., deriving from the presence of high amounts of Cl) when aiming at the direct determination of Br in solid samples by HR CS GFMAS. The accuracy of the method was evaluated via analysis of two different reference materials, poly(vinyl chloride) and tomato leaves.