Kinetics of the solvolysis of the cis-chloroazidobis-(1,2-diaminoethane)cobalt(III) ion in water+t-butanol mixtures

Summary Rate constants for the solvolysis of the complex ioncis-[Coen₂N₃Cl]⁺ have been determined for a range of temperatures in mixtures of water witht-butanol ranging up to 50% v/v of the latter. Linear plots of log (rate constant) against the reciprocal of the absolute temperature are obtained at all concentrations oft-butanol and the variations of the enthalpy and entropy of activation with solvent composition show extrema at compositions where extrema occur in the physical properties of the mixture which are influenced by solvent structure. The importance of solvent structure is shown by the curved plot found for log (rate constant) against reciprocal of dielectric constant at constant temperature. The application of a free energy cycle to the free energies of activation in water and in the mixture and the free energies of transfer of individual ionic species between water and the mixtures shows that the effect of changes in solvent structure on the reacting cation in the transition state dominates over that in the initial state.     

An uncertainty budget for the determination of the purity of glyphosate by quantitative nuclear magnetic resonance (QNMR) spectroscopy

An uncertainty budget is presented for the results of measurements of purity of the agrochemical glyphosate using ¹H and ³¹P quantitative nuclear magnetic resonance (QNMR) spectroscopy. The budget combines intralaboratory precision from repeated independent measurements of a batch, and other Type A and Type B effects. Consideration of correlation of uncertainties in ratios of mass determinations has been included. Expanded uncertainties of the purity for single determinations of purity by ¹H and ³¹P QNMR are 0.66% and 0.82% (95% confidence interval, k=2), respectively.     

Rates of Dissociative Ionic Reactions in Aqueous Mixtures Correlated with Opposing Gibbs Energies of Transfer of Single Ions: Solvolysis of Chloropentacyanocobaltate(III) Anions in Water + Ethanol and Water + Urea

The kinetics of the solvolysis of Co(CN)₅Cl^3– have been investigated in water with an added structure former, ethanol, and with added urea, which has only a weak effect on the solvent structure. As this solvolysis involves a rate-determining dissociative step corresponding closely to a 100%; separation, Co³⁺ Cl^-, in the transition state, a Gibbs energy cycle relating Gibbs energies of activation in water and in the mixtures to Gibbs energies of transfer of individual ionic species between water and the mixtures, G _t ^o (i), can be applied. The acceleration of the reaction found with both these cosolvents results from the compensation of the retarding positive G _t ^o (Cl^- by the negative term [G _t ^o [Co(CN) ₅ ^2- ]-G _t ^o [Co(CN)₅Cl^3- arising from G _t ^o [Co(CN)₅Cl^3-]> G _t ^o [Co(CN) ₅ ^2- ]. Moreover, only a small tendency to extrema in the enthalpies and entropies of activation is found with both these cosolvents, as was also found with added methanol or ethane-1,2-diol, but unlike the extrema found when hydrophobic alcohols are added to water. With the latter, much greater negative values for G _t ^o [Co(CN) ₅ ^2- ]- _t ^o [Co(CN)₅Cl^3-] are found. When G G _t ^o [Co(CN) ₅ ^2- ]-G G _t ^o [CO(CN)₅Cl^3-] becomes low enough not to compensate for the positive G _t ^o (Cl^-), as with added hydrophilic glucose, the reaction is retarded. Compensating contributions of the various G _t ^o (i) involved in the Gibbs energy cycle with added methanol or ethane-1, 2-diol allow log (rate constant) to vary linearly with the reciprocal of the relative permittivity of the medium.     

Certified reference materials chlorobiphenyls (IUPAC nos 28, 52, 101, 118, 153 and 180) in dried sewage sludge — CRM 392

Summary Six chlorinated biphenyls — CB IUPAC nos 28, 52, 101, 118, 153 and 180 — have been certified in a dried sewage sludge of a mainly residential area. After a thorough preparation the material has been studied for the within- and between bottle homogeneity as well as for its long term stability. The certification of the CBs in the dried sludge has been performed with 18 well trained laboratories, applying different methods of extraction, clean-up and chromatographic separation. ECD has been used as final detection and MS to verify the peak identities. All methods for the homogeneity and stability studies as well as those used for the certification campaign are described. CB 138 could not be certified as it co-eluted with CB 183. The major precautions followed by the participants to ensure traceability of the results to the basic units are also discussed. They highlight the level of quality control requested from certifying laboratories. The certified values were obtained after a technical discussion of the methods followed and of each of the individual results. They are given together with the indicative value for CB 138+CB 163.