The compositions of solutions containing arginine and calcium (II) or magnesium (II) were studied at 25 C and 1.00 mol dm À 3 NaCl or 1.00 mol dm À 3 NaClO 4 , as ionic media. The complex formation in 1.00 mol dm À 3 NaCl was studied by measuring the electromotive force of a galvanic cell, involving a glass electrode, to obtain the free hydrogen ion concentration. The investigation in 1.00 mol dm À 3 NaClO 4 was carried out by measuring the electromotive force of two galvanic cells. The former involved a glass electrode whereas the latter used a silver electrode.The investigation was performed in a wide range of reagent concentrations so that experimental data could be explained for calcium (II) by assuming the presence of 1 : 1 and 1 : 2 complexes, both in 1.00 mol dm À 3 NaCl and 1.00 mol dm À 3 NaClO 4 . Experimental data obtained for magnesium (II) were explained by assuming only the formation of 1 : 1 complexes. In both cases the values of the stability constants were determined. A comparison between the results obtained in 1.00 mol dm À 3 NaCl and 1.00 mol dm À 3 NaClO 4 was performed. An attempt to explain as the complex formation takes place in solution is proposed.

Arginine is an important amino acid involved in the production of NO, which is a vasodilatator. Its property as ligand towards cations was little studied. Also its protonation constants, even if subject of several studies, were not accurately determined. In this paper electromotive force measurements are performed by using a hydrogen electrode to accurately determine the three protonation constant of arginine. At 25°C and in 1.00 mol dm -3 NaClO 4 , as ionic medium, they are log k 1 =12.53 ± 0.05; log k 1 k 2 = 21.36 ± 0.03 log k 3 = 2.20 ±0.07, while in 1.00 mol dm -3 NaCl, the following values were obtained: log k 1 =12.35 ± 0.05; log k 1 k 2 = 21.18 ± 0.03; log k 3 = 2.08 ±0.07. Galvanic cells involving silver and glass electrodes were employed to study the behaviour of L-arginine as ligand towards silver (I). The experimental data, obtained at 25°C and in 1.00 mol dm -3 NaClO 4 , were explained by assuming the formation of the species Ag(HL) (log β 1,1,1 = 3.79 ± 0.04) and Ag(HL) 2 (log β 1,2,2 = 7.36 ± 0.03) The results of this paper will be used for future investigation.

The flowing of constant direct current allows planning a coulometric method to determine solubility and acidity constants of slightly soluble acids. Coulometry combined with electromotive force (emf) measurements is applied to obtain such parameters for eight bile acids, simple and conjugated with glycine in solutions in real equilibrium and without formation of micellar aggregates. Results, obtained in different ionic media, (1.00, 0.50, and 0.15) mol.dm(-3) NaCl (i.e., in physiologic conditions), are compared with previous data, extrapolated from mixed solvents or obtained in oversaturated solutions. The proposed method is not difficult to perform, and it can be applied to other slightly soluble acids or in very low concentrations, without a complicated elaboration of the experimental data

The influence of the presence of calcium(II) ions in solutions containing sodium and taurocholate ions at 25 degrees C and in 0.5 mol dm(-3) N(CH(3))(4)Cl as the constant ionic medium was studied. The composition and existence range of aggregates formed by taurocholate sodium and calcium(II) were investigated by means of two different procedures. First, the increasing calcium oxalate solubility due to the presence of taurocholate ions was studied as a function of the taurocholate, sodium and hydrogen ions. The free concentration of sodium and hydrogen ions was determined in solutions equilibrated with solid calcium(II) oxalate. After filtration, the concentration of calcium(II) (by atomic absorption spectrophotometry) and that of oxalate were also determined. In the second approach, electromotive force measurements carried out in solutions containing taurocholate, sodium and calcium(II) ions provided hydrogen and sodium ions free concentrations. The results from both procedures could be explained by assuming the presence of aggregates of different composition with the participation of sodium, calcium(II) and taurocholate ions, depending on the concentration of the reagents. No protonated species were present in appreciable concentrations. All the species found have even anion aggregation numbers. A strong analogy with the composition of sodium taurocholate and glycocholate is observed, while a comparison with sodium deoxycholate, glycodeoxycholate and taurodeoxycholate shows wide differences

The formation of micellar aggregates in the presence of calcium(II) ions in solutions containing sodium and taurodeoxycholate ions and their composition at 25 C and in 0.5 mol dm À 3 N(CH 3 ) 4 Cl as constant ionic medium was studied. The study was carried out by means of two different procedures. In the first one, solid calcium oxalate was equilibrated with taurodeoxycholate, sodium and hydrogen ions and the free concentration of sodium and hydrogen ions was determined. After filtration, the calcium(II) (by atomic absorption spectrophotometry) and oxalate concentration were also determined. In the second approach, hydrogen and sodium ions free concentrations were obtained by electromotive force measurements carried out in solutions containing taurodeoxycholate. The results of both procedures could be explained by assuming the presence of aggregates of different composition with the participation of sodium, calcium(II) and taurodeoxycholate ions, depending on the concentration of the reagents. Protonated species were even present in appreciable concentrations. All the found species have taurodeoxycholate aggregation numbers in multiples of three. A mechanism for the micellar aggregates containing calcium and sodium is proposed. Sodium taurodeoxycholate in the presence of calcium(II) forms larger aggregates than does taurocholate in the presence of calcium(II); the building block of the former is a trimer whereas the latter system has lower aggregation numbers and its building block is a dimer or an octamer.

Taurocholate (TC) and taurodeoxycholate (TDC) in aqueous solutions, in the presence of sodium and hydrogen ions can give micellar products, even differently protonated. This phenomenon is investigated in this paper to explain whether the assumption of hydrogen ions is to attribute to the micellar aggregates, or to the protonation of taurocholate and taurodeoxycholate, respectively.In the course of this research, often the formation of gel occurred immediately after the mixture of the reagents (sodium, hydrogen ions and anions of bile acids) or after some time, depending on the concentrations of the reagents. No author mentions this evidence, but experiments carried out in the presence of gel are not reproducible because the investigated solutions cannot be considered in real equilibrium.The protonation study was performed by means of electromotive force measurements of a galvanic cell involving a glass electrode, at 25°C and 1.00 mol dm‐3 NaCl, as ionic medium. The obtained protonation constants had the following values: log k1 = 0.07 ± 0.02 for TC and log k'1 = 1.60 ± 0.03 for TDC.

The investigation on calcium (II) oxalate is carried out in order to study its solubility in different ionic media. In the same conditions the protonation constants of oxalate and the stability of complex species have been determined. As the stoichiometric composition of the solid calcium (II) oxalate prepared for the investigation was accurately checked, the salt CaC2O4 x H2O is proposed as universal (chelometry, redox, acidimetry) standard. Results of titrations support this possibility.

The fat of mixture of goat and cow milk, extracted by di-ethylic ether, was gas chromatographically analysed in order to propose an analytical procedure suitable to reveal small additions of cow milk to goat milk. The obtained results show evident differences in the percentages of some fatty acids. An attempt to apply the peak area ratios, corresponding to the methyl esters of fatty acids, suggested by the literature for cow milk did not yield good results. Other ratios suitable to reveal even the presence of low percentages (up to 5 %) of cow milk in goat milk were found and proposed in this paper. Such ratios are sensitive and can be defined markers towards cow or goat milk and also towards extraneous fat like lard or colza seeds oil.