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To develop a new solvent-impregnated resin system for the removal of phenols from water the complex formation of triisobutylphosphine sulfide (TIBPS), tributylphosphate (TBP), and tri-n-octylphosphine oxide (TOPO) with a series of phenols (phenol, thiophenol, 3-chlorophenol, 3,5-dichlorophenol, 4-cyanophenol, and pentachlorophenol) was studied. The investigation of complex formation between the extractants and the phenols in the solvent toluene was carried out using liquid-liquid extraction, isothermal titration calorimetry (ITC), and quantum chemical modeling (B3LYP/6-311+G(d,p)//B3LYP/6-311G(d,p) and MP2/6-311++G(2d,2p)//B3LYP/6-311G(d,p)). The equilibrium constant (binding affinity, Kchem), enthalpy of complex formation (DeltaH), and stoichiometry (N) were directly measured with ITC, and the entropy of complexation (DeltaS) was derived from these results. A first screening of K chem toward phenol revealed a very high binding affinity for TOPO, and very low binding affinities for the other extractants. Modeling results showed that although 1:1 complexes were formed, the TIBPS and TBP do not form strong hydrogen bonds. Therefore, in the remainder of the research only TOPO was considered. Kchem of TOPO for the phenols in toluene increased from 1,000 to 10,000 M(-1) in the order phenol < pentachlorophenol < 3-chlorophenol < 4-cyanophenol approximately 3,5-dichlorophenol (in line with their pKa values, except for pentachlorophenol) in the absence of water, while the stoichiometric ratio remained 1:1. In water-saturated toluene, the binding affinities are lower due to co-complexation of water with the active site of the extractant. The increase in binding affinity for TOPO in the phenol series was confirmed by a detailed ab initio study, in which Delta H was calculated to range from -10.7 kcal/mol for phenol to -13.4 kcal/mol for 4-cyanophenol. Pentachlorophenol was found to behave quite differently, showing a DeltaH value of -10.5 kcal/mol. In addition, these calculations confirm the formation of 1:1 H-bonded complexes.

A fast isocratic HPLC method for analysis of steviol glycosides from Stevia rebaudiana leaves was developed with a high selectivity for nine known steviol glycosides and low eluent consumption. The analytical method was performed on a Purospher Ò STAR RP-18 endcapped 3 lm Hibar Ò RT 250-4.6 column at 50°C with an eluent composition of water (65 vol. %) and acetonitrile (35 vol. %). With a flow rate of 1 mL min -1 , nine known steviol glycosides were detected selectively after 15 min. Method validation for rebaudioside A showed a LOD of 0.0004 mg mL -1 and a LOQ of 0.0038 mg mL -1 . Particularly with regard to moderate solubility, the method is linear up to a concentration of rebaudioside A of 4.8 mg mL -1 . The linear calibration curve was obtained with a coefficient of determination of 0.9997 ± 0.0002 and a total error of 2.01 % RSD (n = 12). The accuracy of the method was determined by the percentage mean recovery rate to 100.99 ± 2.01 %. The intra-day precision was in a range of 0.12 to 1.96 % RSD and the inter-day precision varies from 0.02 to 1.89 % RSD. Small changes in operating conditions like eluent composition (65 ± 2 vol. %), temperature (50 ± 10°C) or flow rate (1 ± 0.2 mL min -1 ) do not affect the performance of the analytical method. The reliable and robust proposed HPLC method can be applied for quantification of steviol glycosides in Stevia rebaudiana Bertoni leaves in laboratories and quality control in industry.

The focus of this investigation is the development of a fast and reliable extractant screening approach. Phenol extraction is selected as the model process. A quantum chemical conductor-like screening model for real solvents (COSMO-RS) is combined with molecular design considerations. For this purpose, phenol distribution coefficients K D of known phenol extractants are determined experimentally and in silico. Molecular variations of different extractants are tested concerning their effect on K D to facilitate extractant improvement. It is shown that K D depends on the molecular structure of the extractant. Calculations with COSMO-RS provide a qualitative trend of simulated extraction efficiency and even a quantitatively correct description of K D. The simulations for alkylamine components are, however, not accurate, which is a well-known problem. During the screening process, phosphorus containing aliphatic substances, especially the trialkylphosphine oxide compound Cyanex 923, were determined as the most promising phenol extractants, which agrees with the state of the art.

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