Suspended probes

If changes have been made to the process (e.g. if incoming water quality cannot be maintained or other uncertainties arise concerning the corrosion behavior of the construction materials) it is possible to incorporate coupons or probes of the material into the plant and monitor their corrosion behavior. This approach may be used to assist in the materials selection process for a replacement plant. Small coupons (typically, 25 x 50 mm) of any material may be suspended in the process stream and removed at intervals for weight loss determination and visual inspection for localized corrosion. Electrical resistance probes comprise short strands for the appropriate material electrically isolated from the item of plant. An electrical connection from each end of the probe is fed out of the plant to a control box. The box senses the electrical resistance of the probe. The probe s resistance rises as its cross-sectional area is lost through corrosion. 

Wall-mounted probes, which measure field rather than electrostatic potential, may seem a better choice than suspended probes, but they suffer from the serious problem that charged fines often adhere tenaciously to the sensing electrodes and other surfaces of probes. These charged particles will shield the sensing electrode from the field within the bed and interfere with the measurements. Probably for this reason, very few attempts to use wall-mounted probes are found in the literature. 

Suspended Probe Measurements Revisited. One group has explored the use of suspended probes to gain more useful qualitative electrostatic data in fluidized beds by developing a capacitive circuit model forthe bed (Rojo etal., 1986). Open-circuit voltages induced on immersed... 

In DTMS the sample suspended in a suitable solvent is applied to a platinum/rhodium filament (Pt/Rh 9 1) of the direct insertion probe. The probe is inductively heated at a rate of 0.5 1 A min 1 to a maximum temperature of 800 °C. This means that the temperature is linearly increased from ambient to 800 °C in 1 2 min. 

To prepare DQAsomes or vesicles composed of dequalinium derivatives, the appropriate amount of bola-lipid (10 mM final) was dissolved in methanol, dried using a rotary evaporator, suspended in 2.5 mL 5mM N-2-hydroxyethylpiperazine-N -2-ethane sulfonic acid (HEPES), pH 7.4, bath sonicated for about one hour followed by probe sonication for 45 minutes (10 W). The sample was then centrifuged for 30 minutes at 3000 rpm, the clear, or in some cases, opaque supernatant collected and the remaining non-solubilized residue lyophilized. The concentration of solubilized bola-lipid can be determined spectrophotometrically or can be inferred from the amount of recovered compound after lyophilization. 

Use the clamp to suspend the test tube in the hot water bath. After the BHT has melted completely, reposition the clamp so the test tube is not over the hot water bath or the hot plate. Place the temperature probe into the BHT mixture and press ENTER on the calculator to begin collecting data. 

The solids analysis described above can be taken to yet another level by correlating the color measurement to chemical properties. An excellent model system is vanadium pyrophosphate (VPO), which is a well-known catalyst for butane oxidation to maleic anhydride. During the synthesis of the catalyst precursor, solid V2O5 particles are dispersed in a mixture of benzyl alcohol and i-butanol. In this slurry phase, the vanadium is partly reduced. Addition of phosphoric acid leads to a further reduction and the formation of the VPO structure. With a diffuse reflectance (DR) UV-vis probe by Fiberguide Ind., the surface of the suspended solid particles could be monitored during this slurry reaction. Four points can be noted from Figure 4.4 ... 

TLC-MS-MS has been developed using either manual or instrumental approaches for sample introduction into the MS-MS section. For manual TLC-MS-MS, the spot or zone containing the analyte is removed from the plate after suitable concentration and, if FAB or LSIMS is going to be the ionization technique, it is suspended in a liquid matrix such as glycerol. The resulting mixture is then applied to the probe tip to be introduced into the spectrometer in the usual way. Although this approach involves manipulation of the sample and thus the potential for loss of some of the spatial resolution obtained by the TLC separation, it is readily implemented and requires no additional equipment or interface. 

The Kelvin probe inspired the design of another solid-state device called the Suspended Gate Field-Effect Transistor (SGFET) (Blackburn et al., 1983). It resembles the Kelvin probe in that the gate conductor is suspended approximately 1 jU m above the gate insulator, thus forming a gap of a capacitor (Fig. 6.30). 

In a third configuration, a probe is dipped into the vessel only when it is time to make a measurement in the vessel. Once the data have been collected, the probe is withdrawn. This minimizes the flow disturbance in the vessel, while still allowing sampling at the same location as the sipper tube. A disadvantage of this method is that a film may form on the optical surfaces of the probe as they dry while the probe is suspended in air over the dissolution bath. 

A. van Hoek, and D. N. Reinhoudt, Flexibility of enzymes suspended in organic solvents probed by time-resolved fluorescence anisotropy. Evidence that enzyme activity and enantioselectidty are directly related to enzyme flexibility,... 

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