Method development for determination of organic fluorine in gasoline and its components using high-resolution continuum source flame molecular absorption spectrometry with gallium fluoride as a target molecule

Abstract

High-resolution continuum source molecular absorption spectrometry (HR-CS MAS) has been developing fast for fluorine determination, but neither flame nor graphite furnace technique have ever been applied for the analysis of petroleum or its products. Hydrogen fluoride can be applied in technologies of gasoline components production, unfortunately, arising organic fluorides can contaminate final product. The aim of this work was development of fast and simple HR-CS MAS method, with an ordinary air-acetylene flame, for determination of organic F in gasoline and its components. Gallium fluoride as a target molecule was the imposing choice, because Ga undergoes atomization at relatively low temperature, and the GaF molecule is known to provide good sensitivity in F determination. Severe difficulties have arisen to get higher concentration of gallium (as Ga(III)acetylacetonate) in the measured (xylene) solution. Furthermore, depending on the flame character, the spectrum of the GaF molecule at the most sensitive 211.248 nm rotational “line”could have been disturbed by intensive noise (a case of too rich flame) or overlapped by the OH molecule spectrum (a case of too lean flame). The effects, as well as sensitivity of F determination, depended on the sample volatility and its dilution ratio. The difficulties have been overcome by adjusting the solution aspiration rate and the additional air flow rate to get not-disturbed baseline. The least square background correction (LSBC) with the OH molecule spectrum as the correction spectrum (the OH molecule spectrum intentionally generated for the first time) and the standard addition calibration have been also applied. Huge difference in sensitivity, up to one order of magnitude, depending on the F compound volatility and its chemical character was stated. A standard giving the best sensitivity (heptafluorobutanol) turned out to be the most suitable for calibration in analysis of real samples (satisfactory agreement with results of combustion ion chromatography). It was found that HF introduced into the solution of the investigated sample does not contribute to the increase of F signal. Using 5000 mg L−1 of Ga in a solution, the best characteristic concentration and detection limit are 3.2 mg L−1 and 0.93 mg L−1, respectively. The developed method enabled to identify high contamination of some gasoline components with organic F species, which constituted significant corrosion and environmental threat.