Static and flow methods

In this method the best features of static and flow methods are combined to give the best results. Other advantages are, there is no need to ensure a uniform flow, provided the mixing is satisfactory, the volumes of reactant solutions required are very small. Stopped flow methods have been used for many enzyme reactions. The method is adaptable for gas phase reactions also. 

The progress of a reaction can be followed by several different methods, divided principally into physical and chemical methods and into static methods and flow methods. 

Some workers have experimented with oxidation under static conditions. According to Rezl and Janak [12], good results can be obtained by combining the static and dynamic methods. They recommend that the chemical decomposition should take place in an inert atmosphere under static conditions and that the sample should have a layer of a catalyst on it final oxidation takes place in a flow-through reactor in a layer of oxidation catalyst. 

Hala jet (8) classify VLE measurement techniques in five major groups distillation methods, circulation methods, static methods, dew-point/bubble-point methods, and flow methods. One could add to this list some rather specialized techniques, but in the main most modern low-pressure VLE work is done on two major types of equipment circulation stills and static equilibrium cells. 

In all the above-mentioned studies, the analyses were performed statically in a spectrophotometer cuvette. However, over the years, with the discovery and refinement of analytical techniques, the development of automation systems and flow methods for the analysis of antioxidant capacity has been possible. Table 29.4 shows examples of the application of flow injection analysis (FIA), sequential injection analysis (SIA), multisyringe... 

The published data on the temperature dependence of the total rate constant 13 = ka + kf, of this reaction are presented in Table 4.6. The reaction was studied in both static and flow-type reactors using different methods for detecting the NH2 and OH radicals. The divergence, although insignificant, between the results of independent authors is observed. 

The minimum value of the BET surface area correctly determined by either static or flow method may be derived as follows. The adsorbed amount is evaluated as the difference between the amount introduced in the cell, and the gas phase remaining in the dead space. The main uncertainty about the device volumes concerns the cell dead space. So, the following ratio ... 

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

Since the static pressure loss for a hood is dependent on form and flow rate it can be used alone to monitor rhe flow rate into the hood. If the flow rate and the pressure loss were measured at the same time as the efficiency, the pressure loss can be used for monitoring hood performance. These methods are also described in the literature mentioned above. 

For example, a microwave discharge on H2 in an inert diluent, such as argon gas, is an efficient method for producing H atoms as reactants. Subsequent reaction of these H atoms with NO2 will yield OH and NO, and can serve as a useful source of hydroxyl radicals. These methods of reactant formation are well suited for experiments involving either static or flow reactor systems. 

Depending on the configuration of the device and the method for sample and reagents introduction, it is possible to classify the systems into static (batch or discrete sampling instrument) or flowing stream, both using continuous-flow or stopped-flow systems. 

This method uses a single hydrant as the Test and Flow hydrant. Static, Residual and Flow pressures are all read from the same hydrant. This technique is considered to produce higher levels of error with the test data than other methods. 

The first publications on SFE of APEO were discussed in a review on analytical methods for APEO [42]. For the determination of alkylphe-nols in sewage sludge and sediment, a SFE technique was optimised, using C02 at 80°C and 351 atm, at a flow rate of 2 mL min-1. Extraction times were 15 min static and 10 min dynamic, with a sample intake of 0.1-1 g [41]. In this method, in situ acetylation of the alkylphenols using acetic anhydride was performed. The extract was washed with an aqueous K2C03 solution to remove co-extracted acetic acid, and cleaned up using 5% deactivated silica. 

Gao and co-workers measured the absorption properties of an Octoliglike material [13] by a batch and a flow methods. Quantitative reaction was reported, and the absorbing ability of the PEI-silica material followed the order of Cu > Cd > Zn at a pFF of 6-7 [13]. They also measured the saturated absorption uptake and reported values for copper(II) of 25.95 mg/g and 50.01 mg/g, respectively, for static and dynamic conditions [13]. 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

---