Application of Tri-n-octylphosphine Oxide as an Ionophorefor a Vanadyl Ion-Selective Membrane Electrode

A sensitive method for determining total vanadium in water samples using colorimetric-solid-phase extraction-fiber optic reflectance spectroscopy

A selective colorimetric-solid-phase extraction (C-SPE) method for the determination of total vanadium in water samples was developed. This method introduced a new variation of C-SPE. The colour reaction is based on the reaction of vanadium(V) ternary complex formed with 1-(2-Pyridylazo)-2-naphtol (PAN) in the presence hydrogen peroxide (H(2)O(2)). In this technique, the target analytes in samples are extracted onto solid matrix loaded with a colorimetric reagent and then quantified directly on the adsorbent surface by using a miniature fiber optic reflectance spectrometer. The measurements were carried out at a wavelength of 589.4 nm since it yielded the largest divergence different in reflectance spectra before and after reaction with the vanadium. The overall time required for the C-SPE procedure was approximately 20 min. The amount of concentrated V is then determined in a few seconds by using miniature reflectance spectrometer. At the optimal conditions, a calibration curve was constructed, revealing a linear range of 0.05-0.52 mg L(-1) and a detection limit as low as 0.01 mg L(-1) while the RSD lower than 2.8%. In order to verify the accuracy of the method, a certified reference water samples (TMDA) were analysed and the results obtained were in good agreement with the certified values. The proposed method was applied to the determination of vanadium in tap water, seawater samples with a recovery for the spiked samples in the range of 98-102%.

A study of the interaction between dialkyldimethylammonium bromides and tri-n-octylphosphine oxide (topo) in mixed monolayers at the air/water interface

The interactions between tri-n-octylphosphine oxide (TOPO) and a series of dialkyldimethylammonium bromides (DXDAB) in mixed Langmuir monolayers have been investigated. The mean area per molecule in mixed monolayers (A12) and the excess area (AExc), exhibited deviations from ideal behavior for all the investigated systems. The molecular interactions have been quantified by the values of the excess free energy of mixing (DeltaGExc). The monolayers stability has been examined with the total free energy of mixing (DeltaGM) values. The obtained results indicate that the length of the hydrocarbon chain in dialkyldimethylammonium salts affects the molecular packing and determines the strength of interactions with TOPO molecules.