Recent Methodology Developments in Soil Fluorine Analysis

Introduction Fluorine (F) is one of several trace elements receiving much attention owing to its possible harmful effects on health and environment. There are many methods used as the standard method of analysis of total F in soil. These include: ion selective electrode (ISE); X–ray fluorescence (XRF); Ion chromatography; Instrumental Neutron Activation Analysis (INAA); and Atomic and molecular spectroscopy. The accuracy of different methods to quantify the presence of F in analytical preparations (soil extracts or solid-phase samples) is dependent on interfering elements such as the Al content of the sample; Al cations form very strong complexes with fluoride ions in acidic conditions (D’Alessandro et al., 2008). Also Al acts as an interfering element in the F-analysis by XRF (An et al., 2012) and INAA (Knight et al., 1977) where it can alter the measured intensity of F. Trace levels of F in soil and water are predominantly determined by potentiometric methods such as ISE. The analysis of F in an aqueous phase using this methodology tends to be sensitive and rapid with a reported recovery rate greater than 90%. However, the accuracy of ISE to quantify the concentration of F in soil is greatly dependent on the accuracy of sample preparation method (Campbell, 1987). NaOH fusion is used to release F ions in the ISE methodology, and this often involves high rates of handling errors. In this paper, NaOH fusion and ISE quantification is benchmarked as the conventional technique for the analysis of F in soil, and we assessed the potential for alternative techniques to be used relative to this benchmark. The total F content measured of twelve diversified soil types, each of which has a long term history (>10 years) of phosphate fertilizer application was assessed with several analytical techniques. The main objective of the current project is to validate the potential of alterative techniques to accurately and consistently quantify the concentration of F in soil.