Single-Bubble Sonoluminescence as a New Technique for Determination of Metals in Mineral Water

Abstract

The application of sonoluminescent spectroscopy for determining the content of Na, K, Mg, and Ca in mineral waters is considered. A technique for preparing mineral water samples for spectral analysis and recording analytical luminescence spectra of these samples is described. For the first time, with a spectral resolution of Δλ = 1 nm, the spectra of a moving single-bubble sonoluminescence (m-SBSL) were obtained for colloidal suspensions in dodecane of SiO₂ nanoparticles (<50 nm) saturated with metal ions by adsorption from “Essentuki № 4”, “Essentuki № 17”, “Ash-tau”, “Rychal-su”, “Borjomi”, “Mtabi”. In these spectra, atomic and ionic lines of metals that are part of mineral water salts are identified: Na, K, Mg, Mg⁺, Ca, Ca⁺. Using artificial mineral water samples containing a known amount of metals in the form of Na, K, Mg, and Ca chlorides, the m-SBSL spectra of modeling samples of nanoparticle suspensions were obtained. The concentration dependences of these metal analytical lines intensities in these spectra are plotted at the wavelengths of their maximum emission: Na 589 nm, K 766 nm, Mg 518 nm, Ca⁺ 393 nm. The possible effect of the anions common in mineral waters Cl^–, CO₃^2–, SO₄^2– on the intensity of Na and K lines was considered separately, which confirmed the insignificance of this effect when varying anions in the composition of the salts used for modeling. Based on the obtained data, the content of metals in the sample of mineral water “Mtabi” was estimated: [Na]=7.3 × 10^–3 M, [K]=5.1 × 10^–3 M, [Ca]=1.9 × 10^–3 M, [Mg]=1.7 × 10^–3 M.