Periodate electrode

Fluorescence burst analysis, a variation of FCS procedures that has an optimum configuration for simple presentation, uses a uniform nanoscopic flow channel with an optically perfect ceiling, uniform cross section, and periodic electrodes that can now be constructed by careful electron lithography techniques.55 By application of controlled electric fields, uniform plug flow of solution through... 

In the late 1990s, Ramos et al. discovered steady electroosmotic flow over a pair of microelectrodes applying an AC voltage and dubbed the effect AC electroosmosis [1]. Around the same time, Ajdari predicted ACEO flow over periodic electrode arrays and showed how the effect could be used for long-range pumping [2]. As the performance of ACEO pumps has advanced [3, 4], ACEO has also been exploited, in conjunction with dielectrophoresis (DEP), in different geometries to manipulate particles and cells in microfluidic devices [5-7]. 

There are several ways to design ACEO pumps by breaking symmetry in a periodic electrode array. Ajdari originally suggested modulating either the electrode capacitance via a dielectric coating (Fig. 3a) or the surface height (Fig. 3b) with half the spatial period of the array,... 

AC Electro-Osmotic Flow, Fig. 3 Sketches of local broken symmetries in a periodic electrode array which lead to global time-averaged ACEO pumping ... 

The use of enzyme-based electrodes has been particularly important in electrode development in the biosensing field and enzymes greatly enhance the specificity of the electrodes The enzyme electrodes can be either potentiometric or voltammetric. Since electrodes based on enzymes are often stable over relatively short periods, electrodes with replaceable enzyme tips may prove useful in water monitoring. 

A novel microengineered instrument with a rather different planar electrode layout has been proposed by Muller [3]. Figure Id shows the device, which uses the microwave ion source described earlier and electrostatic filtering. This time, however, mass selection is based on the filtering action provided by the interaction between the ion beam and a three-phase travelling electrical field, which is created by a periodic electrode structure fed by suitably phased drive signals. 

The layer width is taken from the relation d > 1,5 dg, where dg - thickness of a gas discharge gap. The employment of a resistive layer instead of electrode profiling can significantly simplify the device manufacture. The UV radiation is efficiently converted into a visible one by a number of photo-luminophors, e.g. Zn2Si04 Mn. For stroboscopic registration of fast-proceeding processes the luminophors with short period of luminescence are used, e.g anthracene etc. 

Gas-sensing electrodes have been developed for a variety of gases, the characteristics for which are listed in Table 11.4. The composition of the inner solution changes with use, and both it and the membrane must be replaced periodically. Gas-sensing electrodes are stored in a solution similar to the internal solution to minimize their exposure to atmospheric gases. 

These direct-insertion devices are often incorporated within an autosampling device that not only loads sample consecutively but also places the sample carefully into the flame. Usually, the sample on its electrode is first placed just below the load coil of the plasma torch, where it remains for a short time to allow conditions in the plasma to restabilize. The sample is then moved into the base of the flame. Either this last movement can be made quickly so sample evaporation occurs rapidly, or it can be made slowly to allow differential evaporation of components of a sample over a longer period of time. The positioning of the sample in the flame, its rate of introduction, and the length of time in the flame are all important criteria for obtaining reproducible results. 

Application of a pulse of high electric potential (about IkV) to the pusher electrode over a period of about 3 psec causes a short section of the ion beam to be detached and accelerated into a TOP analyzer. A positive potential is used to accelerate positively charged ions and vice versa for negative ions. 

Electromagnetic flow meters ate avadable with various liner and electrode materials. Liner and electrode selection is governed by the corrosion characteristics of the Hquid. Eor corrosive chemicals, fluoropolymer or ceramic liners and noble metal electrodes are commonly used polyurethane or mbber and stainless steel electrodes are often used for abrasive slurries. Some fluids tend to form an insulating coating on the electrodes introducing errors or loss of signal. To overcome this problem, specially shaped electrodes are avadable that extend into the flow stream and tend to self-clean. In another approach, the electrodes are periodically vibrated at ultrasonic frequencies. 

In an alternative procedure (84), the electrolyte is pumped through the cells at such a rate that the outlet concentration is 50 g/L MnSO and 67 g/L H2SO4. This spent electrolyte is then mixed with equal parts of make-up solution containing 150 g/L MnSO and the mixture returned to the electrolysis step. The electrolysis is continued over a period of days and terrninated when the EMD layer deposited on the anode reaches a specific thickness, usually on the order of 1—3 or 6—8 mm. Following completion of the electrolysis cycle, the entire electrode assembly is removed from the cell for removal of the deposited EMD, either manually or by an automated system (85). The product is repeatedly washed with water to extract the occluded acid (83) and dried at about 85°C in air. 

The potentiometric micro detection of all aminophenol isomers can be done by titration in two-phase chloroform-water medium (100), or by reaction with iodates or periodates, and the back-titration of excess unreacted compound using a silver amalgam and SCE electrode combination (101). Microamounts of 2-aminophenol can be detected by potentiometric titration with cupric ions using a copper-ion-selective electrode the 3- and... 

Other commercial cells designed for the electrolysis of fused sodium chloride iaclude the Danneel-Lon2a cell and the Seward cell, both used before World War I. The former had no diaphragm and the sodium was confined to the cathode 2one by salt curtains (ceramic walls) the latter utili2ed the contact-electrode principle, where the cathode was immersed only a few millimeters ia the electrolyte. The Ciba cell was used over a longer period of time. 

---