A simple and low-cost method for fluoride analysis of plant materials using alkali extraction and ion-selective electrode

Backgrounds: Existing methods for fluoride (F^-) determination in plant material require expensive equipment and specialized reagents. This study aimed to develop a simple and cost-effective method for fluoride analysis in plant samples. Results: Using an orthogonal assay design with certified reference material, this study optimized a sodium hydroxide extraction method (5 mol·L^-1) with heating at 120 °C for 0.5 h, followed by the addition of potassium acetate, ionic strength adjustment, and measurement via an ion-selective electrode. The method achieved a limit of detection (LOD) and limit of quantification (LOQ) of 1.41 and 4.71 mg·kg⁻¹, respectively. Recovery rates ranged from 84.74 to 89.34% in Arabidopsis thaliana (intraday relative standard deviation [RSD] ≤ 2.31%, inter-day RSD ≤ 4.17%) and from 83.53 to 91.55% in Camellia sinensis (intraday RSD ≤ 3.11%, inter-day RSD ≤ 4.98%). In A. thaliana cultivated in NaF-dosed (500 µM) nutrient solution, the fluoride concentration in the shoot was 16.00 mg·kg^-1; In C. sinensis grown under 250 µM NaF treatment, the shoot fluoride concentration was 292.71 mg·kg^-1. Moreover, the fluoride concentration in Tea products purchased from local supermarkets ranged from 16.28 to 61.78 mg kg^-1. Conclusion: This study presents a simple, reliable, and cost-effective method for fluoride analysis in plant materials, which can be further validated through inter-laboratory testing to establish a standardized approach.