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

The use of sonoluminescent spectroscopy to determine the content of Na, K, Mg, and Ca in mineral waters is examined. The procedure for preparation of samples of mineral waters for spectral analysis and recording the analytical luminescence spectra is described. For the first time single-bubble sonoluminescence spectra with a resolution of Δλ = 1 nm in bubble motion mode (SBSL-MM) were obtained for colloidal dodecane suspensions of SiO₂ nanoparticles (<50 nm) saturated with metal ions by adsorption from Essentuki No. 4, Essentuki No. 17, Ash-tau, Rychal-su, Borjomi, and Mtabi mineral waters. The atomic and ionic lines of the metals that are part of the salts in the mineral water (Na, K, Mg, Mg⁺, Ca, Ca⁺) were identified in the spectra. Artificial samples of mineral water containing known amounts of the metals in the form of Na, K, Mg, and Ca chlorides were used to obtain the SBSL-MM spectra of model samples of nanoparticle suspensions, and the concentration dependences of the intensities of the analytical lines of these metals in the given spectra at the wavelengths of their maximum luminescence were plotted: Na 589 nm, K 766 nm, Mg 518 nm, and Ca⁺ 393 nm. The possible influence of the Cl^–, \({{\text{CO}}}_{3}^{2-}\) ${\text{CO}}_3^{2-}$ , and \({{\text{SO}}}_{4}^{2-}\) ${\text{SO}}_4^{2-}$ anions commonly found in mineral waters on the intensity of the Na and K lines is examined, and the insignificance of this effect with variation of the anions in the composition of the salts used for modeling is confirmed. The content of the metals in the sample of "Mtabi" mineral water was estimated from the obtained data: [Na] = 7.3∙10^–3 mole/L, [K] = 5.1∙10^–3 mole/L, [Ca] = 1.9∙10^–3 mole/L, and [Mg] = 1.7∙10^–3 mole/L.