Solid sampling determination of total fluorine in baby food samples by high-resolution continuum source graphite furnace molecular absorption spectrometry

Quantitative fluoride imaging of teeth using CaF emission by laser induced breakdown spectroscopy

In this work, we propose the use of molecular emission of calcium fluoride (CaF) by laser induced breakdown spectroscopy (LIBS) to obtain quantitative fluoride distribution images of teeth. LIBS has proved to be an efficient technique to detect low amounts of fluoride in solids, and human teeth have the advantage being a matrix rich in calcium. We used new calibration material from sintered hydroxyapatite pellets doped with fluoride to determine the optimized LIBS conditions of argon flow at 1 L min-1 and using the green emission bands of CaF in 530 nm, and obtained a calibration curve between 0 and 400 μg g-1, and LOD of 18 μg g-1. This methodology was applied within a rat model of fluoride exposure and showed increasing tooth-fluoride with increased exposure dose. To demonstrate applicability of this method in human teeth, we quantified fluoride distribution in teeth from three children from non-fluorinated and fluorinated water regions. Samples from children living in fluoridated water regions showed higher fluoride concentrations in dentine formed after birth, compared to a child from a non-fluoridated region. Teeth have been used as biomarkers for environmental exposure and this new method opens the opportunity in epidemiology research to study critical windows of early life exposure to fluoride as well.

CaI and SrI molecules for iodine determination by high-resolution continuum source graphite furnace molecular absorption spectrometry: Greener molecules for practical application

A new method to determine iodine in drug samples by high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) has been developed. The method measures the molecular absorption of a diatomic molecule, CaI or SrI (less toxic molecule-forming reagents), at 638.904 or 677.692nm, respectively, and uses a mixture containing 5μg of Pd and 0.5μg of Mg as chemical modifier. The method employs pyrolysis temperatures of 1000 and 800°C and vaporization temperatures of 2300 and 2400°C for CaI and SrI, respectively. The optimized amounts of Ca and Sr as molecule-forming reagents are 100 and 150µg, respectively. On the basis of interference studies, even small chlorine concentrations reduce CaI and SrI absorbance significantly. The developed method was used to analyze different commercial drug samples, namely thyroid hormone pills with three different iodine amounts (15.88, 31.77, and 47.66µg) and one liquid drug with 1% m v^-1 active iodine in their compositions. The results agreed with the values informed by the manufacturers (95% confidence level) regardless of whether CaI or SrI was determined. Therefore, the developed method is useful for iodine determination on the basis of CaI or SrI molecular absorption.

High-resolution continuum source graphite furnace molecular absorption spectrometry compared with ion chromatography for quantitative determination of dissolved fluoride in river water samples

In addition to beneficial health effects, fluoride can also have adverse effects on humans, animals, and plants if the daily intake is strongly elevated. One main source of fluoride uptake is water, and thus several ordinances exist in Germany that declare permissible concentrations of fluoride in, for example, drinking water, mineral water, and landfill seepage water. Controlling the fluoride concentrations in aqueous matrices necessitate valid and fast analytical methods. In this work an alternative method for the determination of fluoride in surface waters based on high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS) was applied. Fluoride detection was made possible by the formation of a diatomic molecule, GaF, and detection of characteristic molecular absorption. On HR-CS-GFMAS parameter optimization, the method was adapted to surface water sample analysis. The influence of potential main matrix constituents such as Na⁺, Ca²⁺, Mg²⁺, and Cl^- as well as surface water sampling/storage conditions on the molecular absorption signal of GaF was investigated. Method validation demonstrated a low limit of detection (8.1 μg L^-1) and a low limit of quantification (26.9 μg L^-1), both sufficient for direct river water sample analysis after 0.45-μm filtration. The optimized HR-CS-GFMAS method was applied for the analysis of real water samples from the rivers Rhine and Moselle. For method validation, samples were also analyzed by an ion chromatography (IC) method. IC and HR-CS-GFMAS results both agreed well. In comparison with IC, HR-CS-GFMAS has higher sample throughput, a lower limit of detection and a lower limit of quantification, and higher selectivity, and is a very suitable method for the analysis of dissolved fluoride in river water. Graphical abstract High-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS-GFMAS) was applied for the quantitative analysis of dissolved fluoride in river water samples from the Rhine and the Moselle. Fluoride detection was made possible by the addition of Ga for GaF formation and analysis of characteristic molecular absorption at 211.248 nm. Good agreement between HR-CS-GFMAS and ion chromatography (IC) results was obtained. In comparison with IC, HR-CS-GFMAS had a faster sample throughput and lower limit of detection and limit of quantification.

Method Development for the Determination of Total Fluorine in Foods by Tandem Inductively Coupled Plasma Mass Spectrometry with a Mass-Shift Strategy

A method for total F determination in food and tea samples based on a mass-shift strategy using tandem inductively coupled plasma quadrupole mass spectrometry (ICP-MS-MS) was developed. This method consists of four steps: (1) conversion of the hardly ionized F atoms to BaF⁺ via ICP, (2) use of the first quadrupole (Q1, set at 157) to ensure only the m/z 157 ions (i.e., ¹³⁸Ba¹⁹F⁺, ¹⁵⁷Gd⁺, and ¹³⁸Ba¹⁸OH⁺) enter the reaction cell (RC), (3) shifting ¹³⁸Ba¹⁹F⁺ to a new mass ¹³⁸Ba¹⁹F(¹⁴NH₃)₃⁺ by reacting with NH₃ in RC to avoid the interfering ions (i.e., ¹⁵⁷Gd⁺ and ¹³⁸Ba¹⁸OH⁺), and (4) passing interference-free ¹³⁸Ba¹⁹F(¹⁴NH₃)₃⁺ to the second quadrupole (Q2, set at 208) for detection by the MS detector. The mass-shift process of the target F (in ICP and RC) expected to follow the path: F + ¹³⁸Ba⁺ → ¹⁵⁷BaF⁺ + 3NH₃ → ²⁰⁸BaF(NH₃)₃⁺, while the reaction pathway of dominant ¹⁵⁷Gd⁺ in RC proposed to ¹⁵⁷Gd⁺ + NH₃ → ¹⁵⁷Gd¹⁴N¹H⁺ + nNH₃ → ¹⁵⁷Gd¹⁴N¹H(¹⁴N¹H₃)_n⁺ (n = 0-5). Under the optimized setting of tandem MS (Q1 → Q2 = 157 → 208) and RC reaction gas flow rate (NH₃/He = 10:90, 8.0 mL min^-1), the background equivalent concentrations (BECs) and limits of detection (LODs) were 0.021 and 0.022 μg mL^-1, respectively. The calibration curve was linear in the range between 0.1 and 10 μg mL^-1, with a correlation coefficient of R² = 0.9999. The results obtained for 14 different food-related standard reference materials (SRMs) were in good agreement with the certified values on a 95% confidence level. The proposed method was then employed to evaluate the F contents of 13 branded tea samples. The total F concentrations ranged from 39.2 to 93.2 μg g^-1. The tea infusions contained F between 23.5 and 85.4 μg g^-1, with an extraction efficiency of 56.0-91.6%, and the water-soluble F contents of a Pu'er brick tea were 58.7, 21.4, 3.82, and 1.41 μg g^-1 for filtrates 1, 2, 3, and 4, respectively.