Solvents prepared from natural terpenes (menthol and thymol), as H-bond acceptors, and a series of organic acids (chain lengths of 8, 10, and 14 C atoms), as H-bond donors, were characterized and tested as reaction media for liquid–liquid extraction purposes. Due to their high hydrophobicity, they seem to be promising alternatives to conventional (nonpolar and toxic) solvents, since they possess relatively less toxic, less volatile, and consequently, more environmentally friendly characteristics. Assuming that the equilibrium is established between solvent and analyte during a ligandless procedure, it can be concluded that those nonpolar solvents can efficiently extract nonpolar analytes from the aqueous environment. Previous investigations showed a wide range of applications, including their use as solvents in extractions of metal cations, small molecules, and bioactive compounds for food and pharmaceutical applications. In this work, hydrophobic solvents based on natural terpenes, which showed chemical stability and desirable physicochemical and thermal properties, were chosen as potential reaction media in the liquid–liquid extraction (LLE) procedure for Pb(II) removal from aqueous solutions. Low viscosities and high hydrophobicities of prepared solvents were confirmed as desirable properties for their application. Extraction parameters were optimized, and chosen solvents were applied. The results showed satisfactory extraction efficiencies in simple and fast procedures, followed by low solvent consumption. The best results (98%) were obtained by the thymol-based solvent, thymol–decanoic acid (Thy-DecA) 1:1, followed by L-menthol-based solvents: menthol–octanoic acid (Men-OctA) 1:1 with 97% and menthol–decanoic acid (Men-DecA) 1:1 with 94.3% efficiency.

Implementation of the "bulk liquid membrane" (BLM) system was investigated in terms of its efficiency for selective removal of heavy metal ions from natural resources and industrial wastewater. In this paper, the removal of lead (II) ions through a liquid membrane system and factors that influence the process were examined. The research was performed using the homemade transport cell. Two organic solvents were used as liquid membranes: 1,2-dichloroethane and chloroform. Metal ion concentration in aqueous phases was monitored by flame atomic absorption spectrophotometry, after 4 hours of experiment. Macrocyclic ether (dicyclohexano-18-crown-6) was used as ligand for Pb (II) ions. The effects of nonionic surfactants (Triton X-100, Triton X-45 and Triton X-405) added in the receiving phase of BLM system were investigated. The results showed significant increase in transport rate compared to systems without surfactants. Considering the surfactant structure, transport rate of Pb (II) ions followed the order: TX-100 >TX-45>TX-405. Presence of TX-100 increased transport of Pb (II) ions up to 78% through chloroform and 58% through 1,2-dichloroethane.  

The conductometric study of ligand structure influence on the Pb(II) complexation with crown ethers in different solvents has been investigated. In this paper, the complexation reaction of macrocyclic ligand, 18-crown-6 (18C6), dibenzo-18-crown-6 (DB18C6), and Pb(II) cation was studied in different solvents: dichloromethane (DCM) and 1,2- dichloroethane (1,2-DCE). The effects of surfactant structure (Triton X-100 and Triton X-45) on the conductivity of the Pb(II) complex with 18-crown-6 and dibenzo-18-crown-6 ether have been investigated. The conductance data showed that the stoichiometry of the complexes in most cases is 1:1(ML). It is also demonstrated that the influence of crown ethers is deeply affected by the organic solvent used. In the solvents studied, the stability of the resulting complexes showed higher stability in dichloromethane comparing with 1,2- dichloroethane. Macrocyclic ligand 18-crown-6 showed more suitable for complexation of Pb(II) ions compared to dibenzo-18-crown-6. Adding a surfactant affected the higher absolute values of the conductivity of systems, but not the change in the stoichiometric ratio between a metal ion and macrocyclic ligand.

Green Tea, made from Camellia sinensis plant leaves, is one of the most popular drinks in the world. For the past decades, scientists have studied this plant in terms of potential health benefits. Research has shown that green tea helps prevent stroke, malignancy and infections. In this paper, antioxidant activity and total phenol content of 4 samples of green tea from local Tuzla stores were investigated, of which two were of foreign origin. The antioxidant activity of the samples was analyzed using FRAP and DPPH methods. The obtained results show that the highest content of total phenols and the largest antioxidant capacity has a sample of foreign origin. The content of total phenols in the samples ranges from 60.01 to 79.34 mg GAE/g. The highest FRAP value is 3.34 mmol/g. The antioxidant capacity was also confirmed by the DPPH method. The IC50 value ranges from 0.014 to 0.030 mg/mL. Keywords-Phenol, FRAP, DPPH, Green Tea

The electrochemical methods are very good tool for determination of trace concentrations of various species in water samples. The analysis carried out using these methods are usually simple, fast and also the cost of the required equipment is much lower comparing to other instrumental methods. Furthermore, the electroanalytical methods are easy to automate and computerize. Among five major groups of these methods (potentiometry, voltammetry, coulometry, conductometry and dielectrometry), potentiometry and voltammetry attract the greatest attention of researchers. In this paper, experimental results of research related to development of procedures (voltammetric and potentiometric) for the determination of elements in environmental water samples were presented. Due to their common occurrence in environment and possible toxic effects on living organisms, vanadium and nitrate ions were selected for investigation. Optimization of voltammetric procedure for V(V) determination were carried out in matrix containing different surfactants and humic acids, using lead film electrode as a working electrode. Results showed that only nonionic surfactant Brij-35 did not interfere with the voltammetric signal. Other surfactants as well as humic acids reduced the signal, and possibility of their elimination with suitable resins were also investigated. Potentiometric measurements were consisted of preparation and determination of analytical properties of nitrate ion-selective electrodes with solid contact. The results showed that among three different membrane composition, the best response was achieved by membrane containing: Ni(Phen)2, THTDPCl, PVC and NPOE in the ratio of 1:2:33:64 wt. %, respectively. With the detection limit of 2.8 × 10-6 mol L-1, the working concentration range from 5 × 10-5 to 1 × 10-1 mol L-1 and a slope of -55.1 mV per decade, this electrode showed good selectivity to sulfate, acetate, carbonate, dihydrogen phosphate, fluoride and chloride ions, and also good potential reversibility.

A Cloud point extraction (CPE) procedure was presented for preconcentration of lead(II) ions, after complexation by 18-crown-6 (18C6) and extraction with Triton X-100 at proposed experimental conditions. After separation of surfactant - rich phase, content of Pb(II) ions in remaining solution was measured by Flame Atomic Absorption Spectrometry (FAAS). The experimental conditions such as pH, temperature, concentration of Triton X-100, concentration of 18C6, incubation time, type and concentration of added electrolyte, were evaluated. Results showed that among investigated electrolytes (NaCl, Na2SO4 and Na2CO3) the amount of 0.9 mol/L Na2CO3 lowers cloud point temperature of Triton X-100 to 22?C (room temperature during the experiment), thus simplifying the extraction procedure. After an incubation time of 5 minutes and using the concentration of 1.2?10-3 mol/L Triton X-100 and 1.5?10-4 mol/L 18C6 (1:1 stoichiometric ratio for 18C6:Pb), 60% of lead (II) ions were efficiently removed from investigated solution.

Metode određivanja sadržaja teških metala u prirodnim resursima kao i u industrijskim proizvodima, oduvijek su bile predmet brojnih naučnih istraživanja. Metode određivanja metalnih kationa uglavnom su bazirane na principu ″molekulskog raspoznavanja″, koje se zasniva na kompleksiranju metalnih kationa pogodnim ligandima. Efikasnost kompleksiranja uslovljena je kompatibilnošću kationa i liganda, ali i samim okolnostima, tj. medijem u kojem se odvija kompleksiranje.Jedna od tehnika koja se može primijeniti za uspješno razdvajanje i koncentriranje metalnih kationa je transportovanje kroz tečne organske membrane. Proces transporta obuhvata: ekstrakciju, difuziju i povratnu ekstrakciju metalnog kationa. Veća efikasnost kompleksiranja, (veća stabilnost kompleksa) ne mora značiti i efikasniji transport. Veoma značajan je izbor rastvarača kao membrane.U ovom radu su istražene metal-ligand interakcije, sa aspekta vrste rastvarača u kojem se odvijaju. Primjenjene su spektrometrijske (UV/VIS i AAS) tehnike, a istraživanja izvršena na ″model-sistemima″ sastavljenim od: dvovalentnih metalnih kationa (Cd, Pb), liganada               (18-kruna-6, dibenzo-18-kruna-6, TritonX-100), kontra-iona (pikratni ion), te stripping agenasa (tiosulfat). Korišteni su organski rastvarači: dihlormetan, 1,2-dihloretan, hloroform i nitrobenzen. Rezultati su pokazali da među primjenjenim rastvaračima, najveću efikasnost u ulozi tečne membrane ima dihlormetan, kako za sve ispitane metalne katione, tako i za sve primjenjene ligande. Pokazano je da fizičke osobine rastvarača određuju njegovu efikasnost, tako da dihlormetan sa vrijednošću dielektrične konstante (ε = 8.93) nižom od ostalih, kao i manjom viskoznošću (0.4) ima prednost pri izboru kod pripreme tečne membrane za transport ispitanih metalnih kationa.

5 6 ABSTRACT 7 8 Aims: To investigate the competitive behavior of Cd(II) and Pb(II) ions within their equimolar mixtures, during transportation through a bulk liquid membrane, using macrocyclic carriers. Study design: Study was based on transport experiments, using homemade transport cell. Place and Duration of Study: Department of Analytical Chemistry, Faculty of Technology, between September 2017 and February 2018. Methodology: The bulk liquid membrane systems consisted of homemade transport cell constructed for transport of cations. Cell contained three separated phases: two aqueous and nonaqueous membrane phase between them. 1,2-dichloroethane (1,2-DCE) and dichloromethane (DCM) were used as liquid membranes. Macrocyclic ligands: dibenzo-18-crown-6 (DB18C6) and 18-crown-6 (18C6) were used as ligands for cations within the membranes. Both aqueous phases were buffered at pH = 5. Source phase contained an equimolar mixture of investigated metal ions and picrates as counter ions. Receiving phase contained thiosulphate as stripping agent. Duration of transport experiments were 3 hours and concentration of transported cations was measured using flame atomic absorption spectrometry. Results: Higher ligand selectivity for Pb(II) ions resulted with higher transport rates compared to Cd(II) ions: 63.25 % of Pb(II) > 51.80 % of Cd(II) using 18C6 in 1,2-DCE; 38.90 % of Pb(II) > 30.50 % of Cd(II) using DB18C6 in 1,2-DCE; 43.15 % of Pb(II) > 35.40 % of Cd(II) using 18C6 in DCM and 26.75 % of Pb(II) > 8.90 % of Cd(II) using DB18C6 in DCM. Higher selectivity of 18C6 as ionophore is also evident here. 1,2-DCE showed higher efficiency compared to DCM in competitive experiments (unlike individual experiments). Overall transport of Pb(II) in competitive experiments is lower compared to individual ones in DCM membrane: 40.30%<70.40% (with 18C6) and 26.75%<36.05% (with DB18C6). Overall transport of Cd(II) in competitive experiments is lower compared to individual ones in DCM membrane: 35.40%<48.10% (with 18C6) and 8.90<38.25% (with DB18C6). Conclusion: The results showed that higher ligand selectivity for Pb(II) ions lead to higher transport rates compared to Cd(II) ions from their equimolar mixtures. 18C6 was more selective for both cations as ionophore compared to DB18C6. 1,2-DCE showed higher efficiency as membrane solvent in competitive experiments compared to DCM, unlike the individual experiments. Competition between cations decreased their overall transport in DCM, but increased it in 1,2-DCE membrane. 9