Alternating current trap

Amlani et al. [49] combined conventional photolithographic techniques with self-assembly aspects to form a metal-SAM-metal-SAM-metal junction. Au-covered electrodes with a separation of 40-100 nm were covered with SAMs of OPEs or alkanethiols and an Au nanoparticle (d = 40-100 nm) was trapped in the gap between the electrodes by applying an alternating-current bias. An illustration of the system is shown in Fig. 10.13. 

A vitally important aspect of ion trap operation is the ability to impart translational energy selectively to ions via resonance absorption of alternating current (ac) voltages (10-450 kHz) applied to the endcap. Unlike for linear quadrupole (or other multipole) collision cells, the absorption of energy is m/z specific as each m/z in the trap precesses at a specific set of frequencies, the most important of which for MS/MS is ooz, the fundamental frequency of motion in the z dimension, which is defined by... 

The column is 18 inches in diameter by 21 feet in length, fabricated from 0.25-inch plates rolled and butt-welded with 720 inches of weld. Molten potassium chloride is introduced into the column through a trap. The 6-foot fractionating section of the column is equipped with a 6-inch vapor take-off line which serves as a condenser. Electromagnetic alternating current conduction pumps are used for reflux feed to the top of the column and continuous sodium feed to the bottom of the column. 

The principle of this technique is to consider the adsorbent as an electrical resistance, which is heated by the Joule effect when an alternative current is applied. This regeneration is particularly suitable for activated carbon cloths or felts. After saturation of the adsorbent, the filter is heated by the Joule effect and the desorbate is flushed out of the reactor with an inert gas. Then, the solvent is condensed in a cold trap before being recycled. 

Ion traps, ICR eells as well as QITs, are best operated with the number of trapped ions elose to their respeetive optimum, beeause otherwise ion trajectories are distorted by eoulombie repulsion. Henee, external ion sourees in eombination with ion transfer opties eapable of eontrolling the number of ions injeeted are ideally attaehed to ion traps. Currently, MALDI [207] and ESI (Fig. 4.54) [192-194,199,208] ion sourees are predominating in FT-ICR work. The ion produetion may either be regulated by the souree itself, or alternatively, by some deviee to eolleet and store the desired amount of ions from that source until injection into the ICR. For that purpose, linear RF multipole ion traps are often employed (Chap. 4.4.6), [118,209] but other systems are also in use. [195] RF-only multipoles are eommonly used to transfer the ions into the cell (Chap. 4.4.4). For the injeetion, it is important to adjust the conditions so that the ions have low kinetic energy in z-direction in order not to overcome the shallow trapping potential. 

Usually, amides 7 are prepared from acids 6 and amines. C. Gtirtler of Bayer MaterialScience AG in Leverkusen reports (Tetrahedron Lett. 2004,45, 2515) the develop of catalysts for the alternative condensation of an acid 6 with an isocyanate 4. It is particularly exciting that isocyanates are intermediates in the one-carbon degradation of an acid 3 to the corresponding amine. Current practice, if the protected amine were desired, is that the intermediate isocyanate 4 would be trapped with an alcohol, leading to the urethane 5. This newly-reported observation offers the alternative of ending with the amide 7, or perhaps with the sulfonamide 9. 

An alternative approach has been taken by Blom and co-workers, who have developed a model in which the electron and hole currents are limited not by the injection process but by the transport capability of the bulk polymer.47,48 The maximum single-carrier current that can be supported in a trap-free semiconductor is the space-charge-limited current Jscl, given by... 

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