New analytical method for total fluorine determination in soil samples using high-resolution continuum source graphite furnace molecular absorption spectrometry

Fluorine may be present in soil naturally, in the form of minerals (fluorite, fluorapatite and cryolite) or due to environmental pollution. Plants harvested in soils with high levels of this element might be contaminated and consequently they may present toxicological effects, such as necrosis or growth reduction. Hence, the development of reliable and appropriate methods for the accurate determination of F has become of great importance. The aim of this study was the development of an analytical method for F determination in soil samples, monitoring the rotational lines of the CaF molecule by high-resolution continuum source graphite furnace molecular absorption spectrometry using direct analysis of solid samples. All measurements were carried out using the wavelength at 606.440 nm, evaluating the center pixel only, and a standard solution of 7.5 g L− 1 Ca was used as the molecule-forming reagent. The pyrolysis and atomization temperatures were optimized to 900 °C and 2100 °C, respectively; the Ca mass of 75 μg was adequate to guarantee the formation of the CaF molecule in samples and standard solutions. Sample masses up to 0.25 mg were weighted. Fluoride aqueous standard solutions were used for calibration, resulting in a linear working range between 1.5 and 27 ng F. The characteristic mass obtained was 0.13 ng and the limits of detection and quantification were 0.72 and 2.4 ng mg− 1, respectively, calculated for a sample mass of 0.25 mg. A certified reference material of Lake Sediment (LKSD-4, Ontario, Canada) was used to confirm the trueness of the developed method. The value found for F (234 ± 14 ng mg− 1) was in agreement with the certified value (260 ± 40 ng mg− 1), proving that the developed method provides accurate results for F determination in soil samples. Finally, the developed method was applied for the analysis of soil samples from urban and rural areas. Considering all the investigated soil samples, the F content varied between 138 and 232 ng mg− 1.