Protonation measuring equipment

Because of the high reactivity of Grignard reagents, calorimetric measurements require total exclusion of air and moisture and vacuum tight equipment must be used. The following three reactions (equations 3-5) have usually been studied formation, protonation and reaction with bromine. 

The application of PIXE (Proton Induced X-Ray Emission) and micro-PIXE to quantitative analysis of impurities in polyethylene are described. The equipment, sources of background which affect the sensitivity and the precision of PIXE measurements are discussed for both thick and thin targets. A number of applications of micro-PIXE to the identification and location of trace elements in the "Trees" found in the polymer insulation of HV cables are presented. 

Stopped flow and continuous flow methods [11] have been used to follow proton transfer reactions with half-lives in the millisecond range. The stopped flow method which is more popular is essentially a device for mixing the reactants rapidly (typically in one millisecond) together with some means of observing the fast reaction which follows. Proton transfer from p-nitrobenzyl cyanide to ethoxide ion in ethanol/ether mixtures at —77 °C was studied in this way [12]. The reaction was followed spectrophotometrically. The most rapid reaction occurred with ti/2 ca. 2 x 10 2 sec although the equipment was suitable for following reactions with f1/2 ca. 2 x 10 3 sec. A similar method has been used to measure rates of proton transfer between weak carbon acids (for example, triphenylmethane) and bases (for example, alkoxide ions) in dimethyl sulphoxide [13], A continuous flow apparatus with spectrophotometric detection was used [14] to measure rates of ionization for substituted azulenes in aqueous solution (4), reactions for which half-lives between 2 and 70 msec were observed. 

We think that the main reason for this decline of interest is the limited analytical value of proton shielding tensors. Even if one has the necessary equipment (few people have it) and the necessary know-how, it takes a considerable effort to actually measure a proton shielding tensor. For analytical purposes, the combination of line-narrowing m.p. sequences with magic angle sample spinning (CRAMPS) applied to a powder sample will usually be the method of choice (Scheler et al., 1976 Burum et al., 1993 for a recent review, see Maciel et al., 1990). However, the combination... 

The dilatometric method is time-consuming and subject to the bias introduced by the convention described. More recently pulsed Nuclear Magnetic Resonance (pNMR) has been used to measure the relative amounts of liquid and solid fat in a sample, based upon the difference in rates of relaxation of protons in the two phases after the sample has been pulsed (AOCS Method Cd 16-81). With proper calibration this gives a direct determination of the percentage of solid fat, and the results are termed sohd fat content (SFC). The analysis takes less time than dilato-metry, but the equipment is more expensive. 

An NMR spectrometer for SNIF-NMR (Fig. 6.17) (site-specific natural isotope fractionation NMR) measurements [226] must be specifically equipped and adapted, e.g. for deuterium analysis by a high field magnet (e.g. 9.4 T, corresponding to 400 MHz ( H) and 61.4 MHz ( H) resonance frequency, or 11.4 T, corresponding to 500 MHz ( H) and 76.8 MHz ( H) resonance frequency), a specifically adapted H-NMR probe with fluorine lock and proton decoupling, highly stable electronics and software for spectra acquisition and data processing/treatment. Instrumental details... 

A diamond-anvil-cell (DAG) is a small high pressure cell most suitable for the spectroscopic measurement of molecular or atomic diffusion. The DAG is used for various kinds of spectroscopic investigations on liquids and solids at pressures up to several tens of GPa [19-22]. The optically transparent nature of diamond over a wide wavelength span allows in situ optical measurements in combination with conventional equipment such as visible light or infrared spectrometers. The protonic diffusion in ice is measured by a traditional diffusion-couple method, in the present case, with an H2O/D2O ice bilayer. The mutual diffusion of hydrogen (H) and deuteron (D) in the ice bUayer is monitored by measuring the infrared vibrational spectra. The experimental details are described in the following sections. 

NMR (Nuclear Magnetic Resonance) (i> > ) This technique detects the mobility of protons in various energy states. The hydrogen atoms in bound water are at different energy levels than the hydrogen atoms in free water. These energy levels are measured and recorded in the form of NMR spectra. The bound water can be calculated from the NMR spectrum. NMR measurements may be done at any temperature. While NMR may be the most basic method for the measurement of bound water, it requires expensive equipment, trained personnel, and considerable preparation for each experiment. These requirements are not frequently available to the researcher in the paper industry. 

ESR spectra were taken with a Varian V-4200-10A spectrometer equipped with 100 KHz modulation. Hyperfine splittings were obtained by placing proton markers on the spectra, and g-values were obtained from a measurement of the klystron frequency. 

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