Sample polar

The sample-polarity anomaly in current pulses from x-quartz shocked above the Hugoniot elastic limit gave the first indication of unusual conduc-... 

The effect of shock-induced conduction is less distinct in ferroelectrics than in piezoelectrics but is nevertheless apparent from a number of studies. (See Davison and Graham [79D01] and Novitskii [79N03].) Differences in conduction with sample polarity, such as those seen in quartz but of opposite sign, are observed in ferroelectrics. 

Other solid sorbents have been found more suitable than charcoal for a number of compounds. Silica gel and alumina have been used as a complement to charcoal when sampling polar compounds, but water vapor is strongly adsorbed on these sorbents which leads to deactivation of the sorbent and breakthrough of the compounds by frontal elution. Difficulties also arise with compounds that hydrolyze easily. Alternative sorbents for the collection of polar organic compounds which are sensitive to hydrolysis are porous polymers such as the Chromosorb porous polymer series, Porapak porous polymer series, Tenax-GC and Amberlite XAD sorbent series. 

Figure 2.5 Schematic measuring system for simultaneous measurements of sample polarization and displacement. After [15].

In LLC systems there is not a substantial difference between the selectivity characteristics in the normal phase and the reversed phase mode. The choice of either will mainly be determined by the sample. Polar samples (in polar solvents) will preferably be injected in a reversed phase system and non-polar samples in a normal phase system. 

The application of a strong static electric field modifies the quadrupole coupling constant as an effect of the sample polarization. The phenomenon has been reviewed by Lucken s) who mentions some results concerning halogens. 

Figure 5 Sample polarization curves for copper and steel samples.

The choice of the chemical nature of the stationary phase in a chromatographic column determines at least in part the range of compounds that can be analyzed. This chemical nature is selected based on the composition of the sample (polarity, volatility, etc.) and offers an important practical procedure for obtaining larger values for a (and therefore a better separation). An example showing the separation of the same material on two different columns can be seen in Figures 5.2.10 and 5.2.11. 

Near-critical pSFC applications can be described as those where the mobile phase is solvent-modified CO2, pressurized oniy enough to maintain a single phase, with temperatures near (typically less than) the critical temperature. Many commercially available HPLC bonded silica phases have been used with modified-CO2 mobile phases to achieve normal-phase separations, the choice of stationary phase being dictated by sample polarity. The modifiers added to CO2 accept-abfy overcome the unwanted analyte-silica interactions obeserved with neat CO2 mobile phases. For structural separation of polar compounds such as pharmaceuticals [typically weak acids or bases of molecular weight (MW) <1000], polar phases such as diol-, amino-, and cyano-bonded silica (or bare silica)... 

In Figure 9 one can the dependence of the enhancement factor F on the resonance offset. Curve 1 was received without the sample polarization. Each point of the curve obtained after a 2-min polarization of the sample in the magnetic field Bq. Signal detection was performed using the same MW-4 sequence described above. 

Even when the wavelength of the electromagnetic radiation is small relative to the length of the bulk molecular sample, it is often necessary to think of the matter ->radiation interaction in terms of a bulk polarization induced by the radiation and detected via one or more coherence terms of the sample polarization (Mukamel, 1995). When the wavelength is small relative to sample size,... 

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