ABSTRACT
Adsorption of a cationic surfactant allowed to probe the surface reactivity of montmorillonite encapsulated in a composite of alginate hydrogels (A-MMT). Dodecylbenzyldimethylammonium chloride (BAC-12) was the surfactant used for these studies. BAC-12 is part of the widely used surfactant mixture known as benzalkonium chloride. XRD showed that up to three different types of basal spacing (d 001) were present within the composite indicating that as the concentration of adsorbed BAC-12 increases, populations with different adsorption conformational arrangements are present, even unexpanded clay remains. From the SEM-EDS spectra it is observed that the clay is distributed in the whole composite. In addition, the effect of the presence of cationic and anionic biocides on BAC-12 adsorption was studied. Cationic biocides such as tetradecyllbenzyldimethylammonium chlorides (BAC-14) and paraquat (PQ) show a competitive behavior for the clay adsorption sites at BAC-12 low concentration indicating an electrostatic adsorption mechanism. However, the presence of anionic contaminants such as 2,4-D and metsulfuron methyl do not affect surfactant adsorption. In all scenarios is observed an abrupt increase of BAC-12 adsorbed amount reaching values higher than the clay CEC suggesting strong tail-tail interactions. This occurs at concentrations 10 times lower than the CMC of BAC-12 promoted by clay encapsulation in the composite. In these composites the alginate does not affect the surface reactivity of the clay, but the formation of the hydrogel allows it to be easily extracted from aqueous media which makes it an interesting material with a potential use in water remediation.
ABSTRACT
The analysis of the permeation kinetics of new UV filter formulations is of great importance since the kinetic parameters are related to the effectiveness of the product over time. The dynamics of this process can be evaluated by means of the calculation of the permeation kinetic constants, which can be obtained from the respective permeation profiles. This paper is aimed at improving the analytical performance of permeation assays using an on-line automatic system with spectrometric detection avoiding the chromatographic procedure and the usually manual sampling steps required using the traditional Franz diffusion cell. Then, the kinetics of permeation of octyl p-methoxycinnamate loaded in different microemulsions through a synthetic membrane (polyamide) was analysed at real time by UV-Vis and fluorescence spectroscopies. The spectral data were obtained at regular intervals of time (5 min) during 60 min, and the concentration of the permeated UV-filter was at each time calculated using univariate linear calibration. The interference caused by the presence of basil essential oil (oily phase) in some microemulsion samples was overcome using synchronous fluorescence spectroscopy (Δλ = 60 nm) and partial least squares. In all cases, the permeation profiles were obtained (first-order kinetics) and the respective permeation kinetic constants were calculated. The validation of the proposed method was assessed by gas chromatographic-mass spectroscopy and non-significant differences for the obtained permeation kinetic constants were found between methods (p = 0.05). Additionally, a commercial sample was analysed with the proposed methods and the results were validated by high performance liquid chromatography technique.
ABSTRACT
A new simple, rapid and inexpensive analytical method was developed to determine the biodiesel percentage in biodiesel/diesel blends through simple digital images of samples obtained by scanning with a commercial scanner. Soybean biodiesel and petroleum diesel samples were acquired from refineries currently in operation. There were prepared several mixtures within the range 1.5 to 12.0% of biodiesel in diesel oil, using the same procedure as is done in industry. The analytical signals were images recorded with a scanner. This data was decomposed with different color systems: RGB, HSV, HLS, CMYK and Grayscale. Chemometrics models based on color signals obtained from different mixtures of biodiesel/diesel were built. The quantification by using partial least squares (PLS) resulted in a RMSEP value for biodiesel of 0.9% (w/w); this load approximately 10-times smaller than the corresponding calibration range, with a correlation of 0.96 between predicted and reference values.
