K-means clustering and principal component analysis (PCA) are widely used in water quality analysis and management. Nevertheless, numerous studies have pointed out that K-means with the squared Euclidean distance is not suitable for high-dimensional datasets. We evaluate a methodology (K-means based on PCA) for water quality evaluation. It is based on the PCA method to reduce the dataset from high dimensional to low for the improvement of K-means clustering. For this, a large dataset of 28 hydrogeochemical variables and 582 wells in the coastal aquifer are classified with K-means clustering for high dimensional and K-means clustering based on PCA. The proposed method achieved increased quality cluster cohesion according to the average Silhouette index. It ranged from 0.13 for high dimensional k-means clustering to 5.94 for K-means based on PCA and the practical spatial geographic information systems (GIS) evaluation of clustering indicates more quality results for K-means clustering based on PCA. K-means based on PCA identified three hydrogeochemical classes and their sources. High salinity was attributed to seawater intrusion and the mineralization process, high levels of heavy metals related to domestic-industrial wastewater discharge and low heavy metals concentrations were associated with industrial wastewater punctual discharges. This approach allowed the demarcation of natural and anthropogenic variation sources in the aquifer and provided greater certainty and accuracy to the data classification.

A new liquid membrane, mercury(II) ion-selective electrode (ISE) based on 1,3-diphenylthiourea as a neutral carrier was developed. In solubility tests of 1,3-diphenylthiourea in six different plastizicers, tris(2-ethylhexyl) phosphate (TEHP) showed the best performance and was selected for the membrane. Several ISEs were conditioned and tested for the selection of seven metal ions (Hg²⁺, Cu²⁺, Zn²⁺, Pb²⁺, Ca²⁺, Mg²⁺ and Ag⁺). The best Nernstian response was obtained for Hg²⁺ with an experimental slope of 58.6 ± 0.8 mV per decade in the concentration range 6.0 × 10⁻⁶–5.0 × 10⁻⁴ mol l⁻¹; the presence of the complex Hg(OH)⁺ ion explains the slope of the response curve. The ISE showed stable detection reproducibility during 6 weeks, with a practical detection limit of 10⁻⁶ mol dm⁻³ and a high selectivity for Cd²⁺, Pb²⁺, Co²⁺, Cu²⁺, Sr²⁺, Zn²⁺, Ca²⁺, Mg²⁺, Mn²⁺, K⁺, Na⁺ and NH₄ ⁺ ions. Only one interference for Ag⁺ was found. A second linear response curve for Hg²⁺ was obtained at pH 4 with a slope of 30.8 mV per decade in the concentration range 2.0 × 10⁻⁶–2.1 × 10⁻⁴ mol l⁻¹.

Thiourea derivatives (46 aroylthioureas) having different substituents close to the sulfur atom were synthesized and their ionophore potential in ion selective electrodes (ISEs) was examined. Structural considerations were taken into account based on the corresponding heavy-metal ISE parameters. As ionophores, some 1-furoyl-3-substituted thioureas (series 2) gave the best results in Pb(II), Hg(II) and Cd(II) ISEs. The strong intramolecular hydrogen bond in series 2 allows ligand interaction only through the CS group. Substituents on the furan and phenyl rings give rise to low solubility in the membrane plasticizer. 3-Alkyl substituted furoylthioureas improve solubility but enhance oxidative processes with chain length. New X-ray diffraction (XRD) structures and theoretical DFT calculations were considered in the analysis of the substituent influence on the selectivity of ISEs. These new ionophores have advantages because of their stability, simple synthesis and easy modification of the sulfur binding ability resulting from substitution.