Determination of fluorine in herbs and water samples by molecular absorption spectrometry after preconcentration on nano-TiO2 using ultrasound-assisted dispersive micro solid phase extraction

Ewa Stanisz,Magdalena Krawczyk-Coda

doi:10.1007/s00216-017-0589-y

Abstract

This work presents ultrasound-assisted dispersive micro solid phase extraction (USA DMSPE) for preconcentration of fluorine (F) in water and herb samples. TiO2 nanoparticles (NPs) were used as an adsorbent. The determination with slurry sampling was performed via molecular absorption of calcium monofluoride (CaF) at 606.440 nm using a high-resolution continuum source electrothermal absorption spectrometry (HR-CS ET MAS). Several factors influencing the efficiency of the preconcentration technique, such as the amount of TiO2, pH of sample solution, ultrasonication and centrifugation time and TiO2 slurry solution preparation before injection to HR-CS ET MAS, were investigated in detail. The conditions of detection step (wavelength, calcium amount, pyrolysis and molecule-forming temperatures) were also studied. After extraction, adsorbent with the analyte was mixed with 200 μL of H2O to prepare a slurry solution. The concentration limit of detection was 0.13 ng mL−1. The achieved preconcentration factor was 7. The relative standard deviations (RSDs, %) for F in real samples were 3–15%. The accuracy of this method was evaluated by analyses of certified reference materials after spiking: INCT-MPH-2 (Mixed Polish Herbs), INCT-SBF-4 (Soya Bean Flour), ERM-CAO11b (Hard Drinking Water) and TMDA-54.5 (Lake Ontario Water). The measured F contents in reference materials were in satisfactory agreement with the added amounts, and the recoveries were found to be 97–109%. Under the developed extraction conditions, the proposed method has been successfully applied for the determination of F in real water samples (lake, sea, tap water) and herbs.

Highlights

Fluorine (F) in the environment, mainly as fluorides, represent about 0.06–0.09% of the earth’s crust [1]
Due to the relatively high concentrations of calcium in the water and food samples, we decided to investigate the possibility of using calcium monofluoride (CaF) molecular absorption for analytical purposes
The use of ultrasonication to make the solid phase well dispersed allowed to reduce the time of the whole procedure

Summary

Introduction

Fluorine (F) in the environment, mainly as fluorides, represent about 0.06–0.09% of the earth’s crust [1]. Drinking water and food are defined as the primary sources of fluoride intake, but daily exposure depends heavily on the geographical area [2, 3]. In drinking water, it is considered as a beneficial component at levels of about 0.7 mg L−1. Fluoride may be harmful if it exceeds 1.5 mg L−1. It is the limit set by the World Health Organization and is followed in many countries [1, 3, 4]. The most accessible form of fluoride and, the most toxic is intake through drinking water [2]

Methods

Results

Conclusion