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In this study, a new cation-exchange coating for stir bar sorptive extraction (SBSE) based on poly (acrylic acid-ethylene dimethacrylate) monolithic material was synthesized. The effect of polymerization conditions such as the ratio of functional monomer to cross-linker and the content of porogenic solvent on the extraction efficiencies were investigated in detail. The monolithic material was characterized by elemental analysis, scanning electron microscopy and infrared spectroscopy. In order to evaluate the usability of the new coating for the extraction of inorganic cations, the analysis of soluble K+, Mg2+and Ca2+in milk by ion chromatography with conductivity detection was selected as a paradigm. Several extractive parameters, including pH value in sample matrix, desorption solvent, extraction and desorption time were optimized. Under the optimum conditions, low detection limits (S/N = 3) and quantification limits (S/N = 10) of the proposed method for the target cations were achieved within the range of 0.12–0.28 and 0.4–0.92 μg L−1, respectively. The method also showed good linearity, simplicity, practicality and low cost for the extraction of inorganic cations. Finally, the proposed method was successfully used to analyse three different trademarks of commercial milk samples with satisfactory recoveries in the range of 71.1% to 102.8%. [ABSTRACT FROM AUTHOR]

Abstract: A series of five symmetrical and four unsymmetrical diaryl substituted diketo-pyrrolo-pyrroles was synthesized; two unsymmetrical derivatives are reported for the first time. The relationship between the theoretical excitation energies of the S0 → S1 transition, computed by time dependent density functional theory and the experimental positions of 0–0 vibronic bands in the visible absorption (or fluorescence excitation) spectra was studied. Experimental data were obtained from either solution or from low temperature organic solvent glass, in which the progressions of the vibrational structure enabled correct assignment of vibronic sub-bands in some cases. Theoretical calculations predicted that a linear bathochromic and hyperchromic shift would accompany substitution of each phenyl in the parent 3,6-diphenyl-2,5-dihydro-pyrrolo[3,4-c]pyrrole-1,4-dione by providing a more extensively conjugated aryl centre (2-naphthyl, biphenyl, stilbenyl) for the ensuing planar derivatives. Qualitatively, the experimental bathochromic shifts of the 0–0 vibronic sub-bands were in exact agreement with theory, whilst hyperchromic shifts were affected by the very low solubility of the planar, symmetrical derivatives. Deviations from this ideal behaviour were observed for non-planar derivatives (aryl = stilbenyl or 1-naphthyl), for which the dihedral angles describing the aryl, out-of-plane torsions were probably underestimated by DFT. [Copyright &y& Elsevier]