Composition and existence range of aggregates formed by sodium glycocholate in aqueous solutions were studied. Electromotive force measurements provided hydrogen, sodium, and glycocholate ion free concentrations. Lead(II) glycocholate solubility measurements yielded the free concentration of glycocholate ions, as well. Experimental data obtained at 25 °C and at three different concentrations of N(CH3)4Cl, used as a constant ionic medium, can be explained by assuming the presence of aggregates with different compositions, depending on reagent and ionic medium concentrations. The distribution of the species found at the same concentration of ionic medium and close to neutrality remains constant. As expected, the size of the aggregates increases by increasing ionic medium and reagent concentrations. A dimer is the prevailing species at low concentrations, and all of the found species have even anion aggregation numbers. In solutions with the highest concentration and ionic strength, aggregate multiples of eight are present at a high percentage. These results agree with structural investigations that proposed as building blocks of sodium glycocholate micellar aggregates a dimer and an octamer. A strong analogy with the composition of taurococholate aqueous solutions is observed. The comparison with deoxycholate, glycodeoxycholate, and taurodeoxycholate shows wide differences.
The composition and range of existence of aggregates formed by sodium taurocholate in aqueous micellar solutions were studied. Electromotive force measurements were used to obtain concentrations of free hydrogen and sodium ions. Experimental data obtained at 25 degrees C and at three N(CH3)(4)Cl concentrations, used as anionic medium, can be explained by assuming the presence of aggregates with different compositions depending on the reagent concentrations and the ionic strength. Comparison with taurodeoxycholate shows wide differences. Protonated species of taurocholate are observed only at pH less than or similar to 5. At higher pH, the micellar aggregate distribution remains nearly constant at a given ionic medium concentration. As expected, the size of the micellar aggregates increases on increasing the ionic strength. A dimer is found at all concentrations of the ionic medium. All species found have aggregation numbers of anions in multiples of two. The affinity of sodium ions for micellar aggregates is greater than that of N(CH3)(4)(+) ions
Background: Adulteration of diesel fuel by the addition of vegetable oil is a problem that touches several countries around the world and bypasses the complexity of the specifications regarding the automotive diesel fuel distinguishing between customs, fiscal, and commercial–environmental specifications. At an international level, the adoption of the same analysis methods is important for the harmonization processes and the fluidity of the market. In this context, we assist to the diffusion of the same fraud touching several countries or continents since the limit of the same methods are common to many specifications. For several European countries, the revenue lost as a result of this adulteration consists of billions of euros per year. This enormous amount of illicit money feeds organized criminal networks with huge social and environmental damages. Objective: This work presents a GC method to quantify vegetable oils in the range of 0.2–7% (w/w) in adulterated diesel fuel, intended for use as motor fuel, with or without extraneous heavy mineral oil. Methods: Our study was realized on 100 fraudulent samples collected by the Italian fiscal police in regular oil stations and by the Italian fiscal police and customs officers as a consequence of controls on trucks transporting, in suspicious circumstances, “oil” often declared “antistick and anticorrosion oil” or “protective oil.” Conclusions and Highlights: High reliability of results, external validity, ease of replication, simple instrumentation, and sample preparation make this method well suited for a new “smart” protocol for diesel fuels analysis for customs, fiscal, and antifraud purposes.
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