Capillary gap

In nonaqueous media, carbon (graphite) frequently is an optimal anode material, for example, for methoxylation reactions, even in an industrial scale (capillary gap cell, see Fig. 12). It shows an appreciable overvoltage for the oxidation of methanol compared to platinum. 

Fig. 12 Capillary gap cell (From Ref. [4]) 1 bipolar electrode plates,...

A concentric capillary gap cell (up to 800 cm active area) is described in [87]. 

Silyl enol ethers (Scheme 2, Y = OSi ( 113)3) can be dimerized to 1,4-dicarbonyl compounds in good yields. To suppress the methanolysis of the silyl enol ethers, MeCN-5% MeOH is used as solvent and the electrolysis is conducted within one hour by the use of a capillary gap cell, which allows high currents (Table 7, numbers 6 and 7) [59]. 

Some of these processes have been developed for technical conversions and have been summarized in Ref. [228, 229]. The anodic technical production of t-butylbenzaldehyde has been coupled with the cathodic reduction of phthahc anhydride to phthalide in a paired electrosynthesis in a capillary gap cell [230]. Indirect oxidations with Mn +/Mn + or as mediators... 

No greater than a 10% evaporative loss should occur from either the capillary gap or the reagent container in the course of a run. 

The recommended buffer washes must completely eliminate each reagent from a capillary gap or from the surface of a horizontally held slide. 

The Code-On is a capillary gap Stainer. The capillary gap is formed between two slides, each of which may bear specimens. The shdes of a pair are kept approx 150 tim apart by the clamping action of the slide holder, and by raised areas that exist on each slide at the label area and at each of the opposite corners at the end of the slide. The capillary gap, enclosed by the two slides, holds approx 150 tiL of reagent, assuming that the gap fills to a height of approx 1.5 in. from the bottom of the slide pair. 

The efficiency of reagent removal from the capillary gap was assessed by filling capillary gaps between blank slides with peroxidase-streptavidin complex. After picking up the solution, the slide pairs were blotted for 1 min. The slide pairs were then subjected to three changes in buffer, followed by three, 1-min... 

To assess evaporative loss of fluid from filled capillary gaps, clean slide pairs were filled with colored, distilled water. After a 1-min fill, the maximum height of fluid in the gap was marked on each slide pair. Slides were then segregated into two groups one remained exposed to room air, and the other was placed into the closed incubation chamber. At timed intervals, fluid loss in millimeters was recorded. Laboratory temperature was a constant 25°C with a relative humidity of 28%. After 40 min, air-exposed slides had an average loss of 33% of their volume, whereas slides in the incubation chamber lost only 9% in the same time interval. 

Because the 150- iL aliquots of antisera that are placed in the isolons are exposed to the room environment and suffer a potential 50% evaporative loss over 2 h, the optional hood should be required as standard equipment, a beaker of water should be placed in the oven, heated, and allowed to act as a humidity source, slide staining runs should be kept as short as possible, and the three-well reagent isolator should be used whenever possible because of its larger fluid capacity. To prevent excessive evaporative loss of fluids from the filled capillary gaps, it is imperative that the slides be placed in the incubation chamber having a proper seal. If left exposed to room environmental conditions, fluid evaporates from the capillary gaps with resultant reagent concentration. 

Fluid that is flushed from the capillary gap is collected in a waste tray beneath the slide-coverplate assemblies. This tray has a limited capacity and must be drained prior to a staining run. The entire slide-coverplate and reagent carousel area are enclosed within a Plexiglascover during operation, which protects reagents from laboratory conditions (temperature, humidity) and prevents inadvertent contact with the robotic pipet arm during movement. 

To evaluate evaporative loss of fluid from the capillary gap, the instrument was programmed to dispense 100 0,L of colored tap water into the gaps created... 

Ea and Ec are the applied potentials at the electrodes, while iR is the sum of the ohmic drops at the resistances of the electrolyte and, for example, of the diaphragm. The electrolyte resistance is linearly dependent on the electrode distance. Therefore, this distance should be small and a diaphragm should be avoided (undivided cell), if possible. These conditions are best fulfilled by capillary gap cells with gaps of 0.1-0.2 mm. In this case, the concentration of the supporting electrolyte can also be very small. 

If a large space-time yield is also required in the laboratory application, a capillary gap cell (disc-stack) is a good choice (Fig. 22.11). Only the upper-... 

For application in industry, the work-up of the product containing electrolyte must be easy and efficient. With capillary gap cells, the concentration of a supporting electrolyte may be so low that its recovery is not necessary from the economical standpoint. 

There are three types of stainers that apply the reagents to the slides capillary gap stainers, centrifugal stainers, and flat-method stainers (Earle, 2000). 

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