Discontinuous procedure

The relation between the discontinuous procedure of Eqs. (6-124) and the continuous idealization of Eq. (6-126) is the same as that which exists between the sequence of discrete stroboscopic points and the pseudocontinuous motion of the point of the wheel which appears to the eye owing to the persistence of vision. 

Technical approaches must be scientifically valid and clinically relevant, and documentation that the laboratory director has reviewed all procedures on an annual basis is required. A copy of discontinued procedures is to be maintained for 2 yr thereafter, recording initial date of use and retirement date. 

A rapid two-dimensional separation of a microspot of protein solution under high field intensity is a new application of the two-dimensional principle. The various fractions emerge as a series of rays out of the application zone and hence the designation star electrophoresis which was introduced by us in connection with work on human serum proteins (P4). A similar discontinuous procedure was already mentioned by Strain in 1951 (S4, S5) for the separation of metal ions and recently used by Pucar (P8) and applied by Keler et al. (K1) to human serum. 

The most common calorimetric technique is the discontinuous procedure where the adsorptive is introduced in successive steps. The calorimetric cell with its contents (adsorbent and adsorptive) must be considered as an open system (cf. Figure 3.15). It is only when the adsorptive is introduced reversibly and when the step is small enough (so that the amount introduced can be written d n and the pressure increase dp) that the derivation of a differential energy of adsorption (as defined by Equations (2.49) and (2.50)) is possible. Under these conditions, and taking into account the internal energy contributed by the gaseous adsorptive, we can write ... 

The discontinuous procedure is the conventional technique. It is also referred to as the point-by-point procedure. The adsorptive is introduced in successive amounts and at each stage die measurement is made only when adsorption equilibrium is attained. In this way each point on the adsorption isotherm is determined. The original BET technique (Figure 3.1) and all conventional manometric measurements (Figure 3.2) are based on the discontinuous procedure. This is still the procedure most often used with adsorption balances (Figures 3.10-3.12). In principle, it takes account of the requirement that each experimental point of the adsorption isotherm should correspond to thermodynamic equilibrium. 

The continuous approach is more recent and is not yet widely used. In contrast to a discontinuous procedure, the adsorptive is now continuously feeding the adsorbent, so that the point on the adsorption isotherm is continuously moving along the path of the isotherm. By using the term adsorption isotherm we imply that the adsorption system is always at thermodynamic equilibrium. Since the system is now continuously changing we should stricdy speak of quasi-equilibrium (Rouquerol et at., 1988). The fact that this condition was not fulfilled in the first experiments of this type (Innes, 1951 Lange, 1963) unfortunately delayed the development of this procedure. 

Steps 1-4 (Adsorbent weighed and evacuated, buoyancy correction determined and temperature adjusted) are the same as for the discontinuous procedure. 

The results can be presented in the form of a continuous curve of differential enthalpies of adsorption A versus na, as shown in Figure 3.16b, with a resolution which is much higher than that obtained by the discontinuous procedure (Figure 3.16a). If the adsorption calorimeter cannot be easily connected to a well-calibrated and well-temperature-controlled adsorption sonic nozzle set-up, or when the adsorption isotherm is difficult to determine (e.g. if very small amounts are adsorbed), there remains the possibility of determining, separately, the adsorption isotherm by any of the discontinuous or continuous procedures described in Sections 3.3.1 or 3.3.2. A simple procedure can be applied which does not require the gas flow rate calibration ... 

Discontinuous procedures for determining the adsorption isotherms 67 The discontinuous manometric procedure 67... 

The usual method for the spectrometric determination of hydrophobic substances in water is to extract it with a hydrophobic solvent and to evaluate its infrared spectrum (see Sec. 5.1.5.1). This discontinuous procedure cannot be applied in real time and on-line. 

Quantitative IR spectroscopy has turned out to be very usefid for measuring the decay of peroxide concentration or, alternatively, the inaease in the concentration of products from decomposition. Two types of discontinuous procedures have been used at lower reaction temperatures, the peroxide solution is contained in an internal cell (see Figure 3), which is filled and assembled in a glove box under an argon atmosphere. The internal cell is positioned into the optical high-pressure cell and pressurized with n-heptane acting as the pressure-transmitting medium. The assembly is heated to the reaction temperature and the collection of IR spectra is started. In the case that decomposition rate becomes too fast and a major fraction of the peroxide is decomposed before reaaion conditions of constant T and p are reached, the peroxide solution is dirertly fed into a preheated autoclave. The solution is then quickly pressurized and the collection of IR spectra is started. 

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