Formation of calcium monofluoride in graphite furnace molecular absorption spectrometry, part I: Interference mechanisms of competitive metals Ga, Al, Ba, and Sr

Fluorine can be determined via molecular absorption of CaF generated in a graphite furnace of a high resolution continuum source atomic absorption spectrometer (HR-CS AAS). In this study, the formation mechanisms of CaF in a graphite furnace were examined. To differentiate the condensed phase and gas phase interactions during CaF formation, Ca and F were mixed as well as separately pipetted onto a platform. The main mechanism for the formation of CaF was a gas phase combination reaction between Ca and F because CaF was formed irrespective of whether Ca and F were mixed or separated. When solid tea and Ca solution or solid Ca(NO₃)₂ were separately introduced on the platform, a significant CaF signal was observed. Secondly, the interference mechanisms of gallium, aluminum, barium, and strontium on the formation of CaF were researched. The interferents, along with Ca and F, were mixed or separately pipetted onto the platform in various combinations. The results revealed that F and the interferent reacted both in the condensed phase and gas phase. However, a gas phase reaction between F and the interferent metal played a dominant and final role. Because F was shared between Ca and the metallic interferent, the sensitivity for CaF was changed compared to matrix-free standards depending on the interferent and its concentration. In this case, F can accurately be determined only if matrix-matching standards or better are used when the analyte addition technique is applied.