Rapid Field Switching

A significant step in the measurement of MFEs is the development of rapid field switching apparatusModem MOSFET transistors have made the possibility of field switching on the timescale of RP dynamics a reality. This technique was first used in a method called SEMF-CIDNP (switched external magnetic field chemically induced dynamic nuclear polarization). 

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In a time-of-flight (TOF) analyzer the time of flight of ions between the ion source and the detector is measured [61]. This requires that the time at which the ions leave the ion source is well-defined. Therefore, ions are either formed by a pulsed ionization method or various kinds of rapid electric field switching. The single discontinuous laser pulses at distinct time points used in MALDI can be ideally combined with time-of-flight mass separation. TOF analyzers thus received increasing interest with the development of MALDI MS. The schematic draw of a linear MALDI-TOF MS is shown in Fig. (9). 

The simplest technique is pre-saturation in which the solvent is subjected to CW irradiation for a short time at a level sufficient to saturate the solvent without affecting other solute peaks. The saturating field is removed immediately before the observation pulse so that the solvent peak has no opportunity to relax. Several solvent peaks can be saturated if rapid frequency switching can be performed during the saturation period. If proton exchange between solvent and solute occurs, for example exchange of OH and NH with H2O, the solvent saturation can be transferred to the solute. However, this is rarely a problem in synthetic polymers, and because of its ease of application the pre-saturation method is the preferred method. 

The authors have applied polymer/LC composite films as novel permselective membranes [1-8]. The polymer/LC composite film exhibited a distinct and rapid light switching between turbid and transparent states upon off- and on-a.c. electric fields, respectively [9-13]. Also, we proposed a novel type of reversible and bistable light switching by the use of the LCP/LC composite system[l4,15]. 

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