Layered double hydroxide nanoparticles for a smartphone digital image colorimetry-based determination of fluoride ions in water, milk and dental products

Abstract

A novel smartphone digital image colorimetry-based approach was developed for fluoride ion determination, using layered double hydroxide (LDH) nanoparticles (Mg₂Al(OH)₇) as sorbents for analyte preconcentration and as a source of a central metal ion for a colored complex formation. A cotton rotating disk provided effective retention of the LDH nanoparticles during solid-phase microextraction and elution, excluding time-consuming centrifugation process. In the proposed procedure, the nanoparticles acted as aluminum ion source for alizarin complexone-Al³⁺-F^- complex formation. An image of Eppendorf tube, containing the colored complex solution was obtained by a smartphone and converted, using the RGB model for fluoride ion determination. The procedure had a linear range of 0.20-20 mg L^-1 with a limit of detection of 0.06 mg L^-1. The developed procedure provided effective fluoride separation from various matrices for its determination by a smartphone without additional sample pretreatment.

Keywords: Cotton rotating disk; Fluorides; Food; Layered double hydroxide; Smartphone digital image colorimetry; Solid-phase microextraction.