Titration methods magnetic

This review updates a classic and influential review by Halevi.3 What makes the current review timely is the recent development of a nuclear magnetic resonance (NMR) titration method capable of exquisite accuracy and not subject to the systematic error associated with possible impurities in one of the samples and not in the other. New values can now be compared with previous ones. 

These three phases were gently stirred without mixing at 25 i 1 °C using a magnetic stirrer. At specified time intervals, the concentrations of metal picrate in both aqueous phases were determined by UV spectroscopy. It was confirmed by the silver nitrate titration method using 5% potassium chromate as indicator that no chloride ion was transported from, aqueous phase I to aqueous phase II. 

A titration method was employed. The surfactant and oil were first added to a 20 mL glass vial. The mixture was stirred at 300 rpm using a magnetic stir bar (Teflon, Va ). After 1 min, the mixture was diluted with deionized (Dl) water (18.2 mfi-cm, pH 7) dropwise within a 10 s time frame. The emulsion mixture was stirred at 1200 rpm for another 30 min, after which it was removed from the plate and allowed to relax for 6 h to ensure equilibrium. The number of visually distinct phases was counted for each composition lying along the tie lines, shown as the dashed lines in the ternary diagram of Fig. 15.6 Representative compositions for each phase were selected according to Fig. 15.7. 

The side-chain chlorine contents of benzyl chloride, benzal chloride, and benzotrichlorides are determined by hydrolysis with methanolic sodium hydroxide followed by titration with silver nitrate. Total chlorine determination, including ring chlorine, is made by standard combustion methods (55). Several procedures for the gas chromatographic analysis of chlorotoluene mixtures have been described (56,57). Proton and nuclear magnetic resonance shifts, characteristic iafrared absorption bands, and principal mass spectral peaks have been summarized including sources of reference spectra (58). Procedures for measuring trace benzyl chloride ia air (59) and ia water (60) have been described. 

Several modem analytical instruments are powerful tools for the characterisation of end groups. Molecular spectroscopic techniques are commonly employed for this purpose. Nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FTIR) spectroscopy and mass spectrometry (MS), often in combination, can be used to elucidate the end group structures for many polymer systems more traditional chemical methods, such as titration, are still in wide use, but employed more for specific applications, for example, determining acid end group levels. Nowadays, NMR spectroscopy is usually the first technique employed, providing the polymer system is soluble in organic solvents, as quantification of the levels of... 

Equivalent Weight. Three reliable analytical methods are available to determine the equivalent weight of CTPB prepolymer (1) titration by 0.1 N sodium methylate in pyridine solution to the thymol blue end point, (2) infrared spectroscopy, and (3) nuclear magnetic resonance. Satisfactory agreement has been obtained between these instrumental analyses and the acid content as determined by titration (Table XVI). 

In principle the deviation <5 can be determined by the use of usual analytical chemistry or a highly sensitive thermo-balance. These methods, however, are not suitable for very small deviations. In these cases the following methods are often applied to detect the deviation physico-chemical methods (ionic conductivity, diffusion constant, etc.), electro-chemical methods (coulometric titration, etc.), and physical methods (electric conductivity, nuclear magnetic resonance, electron spin resonance, Mossbauer effect, etc.), some of which will be described in detail. 

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