Tensammetry with accumulation on the hanging mercury drop electrode : Part 3. The behaviour of triton X-100 in mixtures with PEG-9000

The behaviour of Triton X-100, which can be present in monomeric or associated form, and its mixtures with PEG-9000, which does not undergo association, is described. The tensammetric curve of Triton X-100 alone shows one or two peaks at negative potentials, depending on the concentration of Triton X-100, i.e., on the presence of associated forms. For <2 mg l^?1, there is one broad peak, related to monomers of Triton X-100. The calibration plot for this peak is sigmoidal but its rising section (0.05–0.20 mg l^?1) is approximately linear. The calibration curve of the second, much narrower, peak related to associated forms of Triton X-100, grows parabolically with increasing concentration of Triton X-100. The behaviour of a mixture of PEG-9000 with a larger amount of Triton X-100 is similar to the behaviour of a model mixture of components with sufficiently different properties (e.g., PEG 1500/PEG 9000). The peak for PEG-9000, the stronger surfactant, is relatively less affected by a large amount of Triton X-100. Even this effect can be decreased by using a suitable preconcentration potential (?1.45 V vs. SCE) so that PEG-9000 can be determined in the presence of a 1000-fold amount of Triton X-100. Both peaks of Triton X-100 are greatly decreased by the presence of PEG-9000 and the broad peak can be completely suppressed. Triton X-100 cannot be determined accurately in the presence of unknown amounts of PEG-9000.     

New Cyclic Dimers of Cholic Acid

Summary. Two new cyclic dimers of cholic acid were obtained in the reaction of 3-O-acetyl methyl cholate with oxalyl chloride. The oxalates bound the cholate subunits side-to-side as a result of acylation of 7 and 12 OH groups in the substrate. The selective deprotection of hydroxy groups at C-3 and C-24 proved to be rather difficult and led to various products depending on the reaction conditions.     

Conductance of HCl in water-sulfolane solvents at 25, 30, and 40°C; a comparison of conductance equations

The molar conductance of solutions of HCl (concentrations from 3×10^–4 to 0.033 mol-l^–1) in water-sulfolane (tetramethylenesulfone) mixtures of mole fractions (X₂) of sulfolane of 0.25, 0.50, 0.75, and 0.85 at 25, 30, and 40°C have been determined. The dielectric constants of the solvents varied from 45 to 60 at 25°C. The data were analyzed by the full Pitts equation, the expanded Pitts equation, and the expanded Fuoss-Hsia equations, all of which give comparable results for the limiting molar conductanceA _o and for the ion-pair association constant K_A for HCl. These equations were unsuccessful for the analysis of supplemental data in pure sulfolane. At 25°C, the pK for dissociation of HCl varies from 0.4 (X₂=0.25) to 2.9 (X₂=0.85). The extent of ion pairing is apparently strongly influenced by selective ion-solvent interactions.On leave 1973–75, Technical University of Gdansk, 80-952 Gdansk Poland.On leave 1980 from Comisión Nacional de Energia Atómica, Buenos Aires, Argentina.     

Formation of [M-H]- and [M-2H]2- ions in the electrospray ionization mass spectra of dicarboxylated polyethylene glycols

The negative-ion electrospray mass spectrometric behavior of dicarboxylated polyethylene glycols (CPEGCs) is discussed. Both [M-H](-) and [M-2H](2-) ions were observed. It was found that the ratio [M-2H](2-)/[M-H](-) is affected by oxyethylene chain length, solvent polarity, analyte concentration and applied cone voltage.     

Solute-solvent interactions in acid-base dissociation: Seven protonated nitrogen bases in water-N-methyl-2-pyrrolidinone solvents

Acidic dissociation constants of seven protonated nitrogen bases, namely Bis-tris, 2-aminopyridine, Tris, morpholine, 2-amino-2-methyl-1,3-propanediol,n-butylamine, andt-butylamine, have been determined at 15, 25, and 35° C in mixtures of water andN-methyl-2-pyrrolidinone (NM2Py). The mole fractions of cosolvent were 0.2, 0.4, 0.6, and 0.8. Glass and silver-silver chloride electrodes were used in a cell without liquid junction, and both the ionic strength and molality of chloride ion remained substantially constant in all of the measurements. The pK _a of all the protonated bases decreases initially and passes through a minimum as the aqueous solvent is enriched with NM2Py. The order of acidic strengths is the same as in the H₂O-dimethyl sulfoxide (DMSO) solvent system, but the pK _a values are all lower by up to 2 units. NM2Py appears to be a more basic solvent than DMSO or H₂O.On leave 1973–1975 from the University of Gdask, Poland.     

Isolation of poly(propylene glycol)s from water for quantitative analysis by reversed-phase liquid chromatography

Procedures for the isolation of poly(propylene glycol)s (PPGs) from a water matrix have been developed. Solid-phase extraction with an octadecylsilica cartridge and elution with methanol or with a graphitised carbon black cartridge and elution with a mixture of dichloromethane-methanol (4:1) or liquid-liquid extraction with chloroform were all suitable for model samples. However, only liquid-liquid extraction was suitable both for model and real environmental samples. Methods for reversed-phase liquid chromatographic determination of PPGs based on derivatisation and ultraviolet or fluorescence detection have been developed. Four derivatisation agents [3,5-dinitrobenzoyl chloride, phenyl isocyanate, 1-naphthoyl chloride and 1-naphthyl isocyanate (NIC)] were tested. Only NIC was found to give good reproducibility as well as a satisfactory detection limit. Finally, a method with liquid-liquid extraction with chloroform, derivatisation with NIC and liquid chromatographic separation with fluorescence detection was established. The developed method shows a highly correlated linearity of the analytical signals of particular homologues within a wide concentration range (approximately from 0.01 to 10 mg l(-1)). The precision of measurements is satisfactory for homologues having 5-9 oxypropylene subunits and becomes worse with an increase in the number of oxypropylene subunits. The limit of detection is 2 microg l(-1) for the majority of homologues. The method is suitable for the isolation and quantitative determination of PPGs in river water samples and as a tool for biodegradation testing.     

Tensammetry with accumulation on the hanging mercury drop electrode: Part 6. Errors of determination caused by adsorption of non-ionic surfactants on the material of the measuring cell

The adosorptive loss of oxyethylated alkylphenols (Triton X-100 and Rokafenol N-3), oxyethylated alcohols (Brij-35, Marlipal 1618/40 and surfactant 18-10) and poly(ethylene glycol) of MW 9000 on cells constructed from quartz, glass, glassy carbon, PTFE, polyethylene, polypropylene, polystyrene and aluminium during the measuring process was investigated. In all instances very substantial losses were found, which completely changed the results of the determination. Apart from the vessel itself, very important losses on the ceramic frit located at the end of the salt bridge were found.The loss of all the surfactants tested on the quartz vessel is not very substantial and, after protection of the ceramic frit, a cell with such a construction gives minimum losses. The glass cell is very sensitivie to the manner of preparation of its surface. Cells constructed from PTFE and glassy carbon adsorb more specifically than others and can be used for the determination of oxyethylated alcohols but not for the determination of oxyethylated alkylphenols. Other materials used gave substantial losses of almost all the surfactants tested. Particularly bad results were obtained with polystyrene and aluminium cells.     

Thermometric titration of some amines in water—acetone mixtures

The enthalpies of protonation of some N-bases in H₂O—acetone, 0, 0.25, 0.5, 0.75 and 0.95 mole fraction at 298 K have been determined by calorimetry. Solutions of amines in each solvent system were titrated enthalpimetrically with HClO₄ solution. The bases studied were piperidine, n-butylamine, 2-amino-2-methyl-1,3-propanediol, (AMP), tris(hydroxymethyl) aminomethane, tris, 2,2-bis-(hydroxymethyl-2,2′,2″-nitrilotriethanol, (bis-tris) and pyridine.The results are discussed in terms of the preferential solvation of ions by two types of solvent molecules. The enthalpy of protonation of all the bases passes through a minimum at a solvent composition of 0.75 mole fraction of acetone.     

Anodic stripping voltammetry of germanium at the hanging mercury drop electrode

The Ge(IV)—Ge(0) system was investigated by cyclic and stripping voltammetry at HMDE in acidic pyrogallol medium and in phosphate, borate and carbonate buffers. It was found that germanium electrodeposited from dilute Ge(IV) solutions dissolved anodically forming two peaks corresponding to the oxidation of the unstable homogeneous and stable heterogeneous amalgams. Both peaks can be exploited analytically for the determination of traces of germanium but due to the complex nature of the germanium amalgam the sensitivity and reproducibility of the determinations are lower compared to the results obtained for metals well-soluble in mercury.     

Cyclic and stripping voltammetry of Se(+4) and Se(-2) at carbon electrodes in acid solutions

The behaviour of the Se(+4)?Se(0)?Se(?2) system was studied by cyclic and stripping voltammetry using several kinds of graphite and glassy carbon electrodes in the pH range from 0 to 8. Well-defined curves of Se(+4) reduction were obtained with a very soft graphite electrode, whereas poorly defined curves were recorded with glassy carbon electrodes. The reduction of Se(+4) in acid solution led to the formation of two forms of elemental selenium. One was formed in a direct electroreduction and the other in a subsequent chemical reaction between Se(+4) and Se(?2). These two forms of Se(0) gave separate reduction and oxidation peaks. Hydrogen selenide was anodically oxidized stepwise to elemental selenium and selenous acid. With an increase of pH the extent of Se(+4) reduction decreased and the extent of Se(?2) oxidation increased.The cathodic and anodic stripping peaks of elemental selenium cannot be used for the determination of traces of Se(+4) because they appear only in solutions with Se(+4) concentrations >1×10^?5 mol 1^?1.