Herein, an electrochemical sensor based on a bilayer composite of phosphomolybdate doped polypyrrole (PPy-PMo 12 ) and nanodiamond (ND) at a disposable gold chip (GCHIP) has been introduced for detection of propylparaben (PP). Electropolymerization was employed for deposition of PPy-PMo 12 layer on a pre-casted ND layer at the GCHIP. The morphology and microstructure were characterized using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Electrochemical behavior of PP at the modified electrode was studied and all the influential parameters were optimized. The calibration curve showed to be linear in the range of 5 to 200 μM of PP. The limits of detection (LOD) and quantification (LOQ) of the method were obtained to be 2.1 and 7.1 μM, respectively. Also, reproducibility of the sensor (RSD%) was 4%. The proposed sensor was employed for detection of PP in unspiked and spiked shampoo samples which yielded recoveries in the range of 93.6-104.4%.

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The complexation reactions between K + , Na + , and La 3+ cations and the macrocyclic ligand dibenzo-18-crown-6 (DB18C6) were studied in acetionitrile (AN)-dimethylformamide (DMF) binary mixtures. Also, the complexation of K + and Na + in 50% ethanol (EtOH)-50% DMF and 50% EtOH-50% AN binary mixtures was studied. The conductivity data show that the stochiometry of all the complexes is 1 : 1. A non-linear behavior was observed for the log K f variation vs. composition of binary solvent, which was discussed in terms of heteroselective solvation and solvent-solvent interactions in binary solutions. It was found that the stability order of the complexes changes with composition of the mixed solvents. The stability sequence for AN-DMF (25 and 50 mol % DMF) solutions and pure AN at 25°C is [K(DB18C6)] + > [Na(DB18C6)] + > [La(DB18C6)] 3+ . However, at 75 mol % DMF it changes to [Na(DB18C6)] + > [K(DB18C6)] + > [La(DB18C6)] 3+ . The thermodynamical values ( , ) for these complexation reactions were determined from the temperature dependence of the stability constants. The thermodynamics of the complexation reactions is affected by the nature and composition of the mixed solvents.

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