ABSTRACT
The quantity rH, an index of the reducing power of a redox system is, in conceptual and operational terms, coordinatively linked with the two familiar electroanalytical quantities: redox potential (EO/R) and pH, and has recently become important in quality and environmental controls (hydrographic network, human consumption waters, industrial effluents, etc.). It has some significant problems of standardization and methodological applications, especially on passing from pure water medium to aqueous-organic media, and the results of the most recent researches are here presented.
Subject(s)
Chemistry Techniques, Analytical/standards , Electrochemistry/standards , Buffers , Chemistry Techniques, Analytical/methods , Chromium/chemistry , Electrochemistry/methods , Environmental Pollutants/analysis , Humans , Hydrogen-Ion Concentration , Hydroquinones/chemistry , Oxidation-Reduction , Reference StandardsABSTRACT
The structural, morphological and surface features on two MCC powders of the same commercial type (Avicel PH 102), but coming from different countries (The Netherlands and Hong Kong) and vendors (DMV International and Mingtai Chemical Co., Ltd., respectively), have been investigated and compared, by means of the X-ray diffraction, SEM and BET and polymerization degree determination. TGA and water sorption from saturated vapor experiments have been applied to characterize and compare the MCC/water interactions of the two samples. The results were integrated by studies of preferential sorption from binary aqueous/organic solvents.
Subject(s)
Cellulose/chemistry , Excipients/chemistry , Solvents/chemistry , Water/analysis , Acetonitriles/chemistry , Adsorption , Dioxanes/chemistry , Ethanol/chemistry , Methanol/chemistry , Microscopy, Electron, Scanning , Powders/chemistry , Temperature , Thermogravimetry , Water/chemistryABSTRACT
The transference numbers t of lithium sulfate in acetonitrile/water and methanol/water solvent mixtures have been studied by measuring the emfs of such transference cells as Pb(Hg)|PbSO(4)|Li(2)SO(4) (m(2))||Li(2)SO(4) (m(1))|PbSO(4)| Pb(Hg), Hg|Hg(2)SO(4)|Li(2)SO(4) (m(2))||Li(2)SO(4) (m(1))|Hg(2)SO(4)|Hg, and Li(x)Hg(1-)(x)|Li(2)SO(4) (m(1))||Li(2)SO(4) (m(2))|Li(x)Hg(1-)(x), in view of characterizing Li(2)SO(4) as an unsymmetrical salt bridge for the minimization of liquid junction potentials in potentiometric applications. In water, Li(2)SO(4) is nearly as good a salt bridge as the popular KCl one. Its effectiveness has been verified through the operational pH-metric cell using various aqueous pH(S) standards. In acetonitrile/water solvents of 0.09 mass fraction of acetonitrile at 298.15 K, Li(2)SO(4) shows exact ionic equitransference, obeying the general condition t(+)/z(+) = t(-)/|z(-)|. The Li(2)SO(4) salt bridge can be used either for simple insertion between two different electrolyte solutions to minimize the intervening liquid junction potentials, as the outer component of a double-bridge arrangement of any commonly available reference electrode, or, obviously, for structural incorporation in sulfate-reversible reference electrodes as the appropriate supporting and bridge electrolyte. The operational potential of the Hg| Hg(2)SO(4)|2 m Li(2)SO(4) reference electrode in aqueous solutions is 0.6326 V at 298.15 K.
