Discontinuous Method

The discontinuous method measures activity by separating the product from the substrate. Assays characteristic of this group usually require two steps, since separation often does not include detection. Thus, first, the substrate and the product are separated, and usually the amount of product formed is measured. Assays that use radiochemical substrates are included in this group, since radiochemical detectors are unable to differentiate between the radiolabel of the substrate and that of the product. Examples of enzymes whose assay methods fall into this category are legion, and these approaches characterized by a separation step. 

As an illustration, consider the assay to measure the activity of the tRNA synthetases. These enzymes catalyze the covalent attachment to tRNA of an amino acid, usually radioactive as follows  

The activity is usually followed by measuring the amount of RNA- AA, the product of reaction (2) formed during the incubation. Since the radiochemical detector cannot differentiate the free radioactive amino acid 

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Two methods for modification of polymer surfaces by photoinitiated graft copolymerization have been developed a discontinuous method (1) with vapor phase transfer of initiator and monomer and a continuous method (2) with presoaking of a film strip or a fiber bundle in a solution of initiator and monomer. Both methods have been applied to polyelefins and linear polyester. 

Application is mainly by padding followed by curing at 150-180 °C, although minimum add-on techniques such as slop padding, spraying and foam application have been successful. They can also be applied by discontinuous methods, such as exhaust or dip-spin [501]. 

Discontinuous methods are performed in conventional separating funnels in one or more steps. In ultratrace analyses, tapered or specially profiled quartz tubes are recommended because of their easier cleaning (more compact size), the introduction of less contaminating material, and easier centrifugation in the case of difficulties with phase separation. Shaking must be continued until equilibrium is reached, which may last seconds, minutes, or (rarely) hours, depending on the physicochemical properties of the system more than 2-5 min requires a mechanical shaker. Microscale extraction carried out in autosampler tubes, followed by direct automatic introduction of the organic phase into the atomizer, is recommended. 

In the manufacture of tetryl, it is usual not to nitrate dimethylaniline directly, but to dissolve it first in concentrated sulphuric acid and then to nitrate the dimethylaniline sulphate so obtained. Straightforward nitration of dimethylaniline proceeds so violently, that it can be carried out only under the special conditions described on pp. 42-43. Many years experience of tetryl manufacture has shown that the ratio of sulphuric acid to dimethylaniline should not be lower than 3 1, a smaller amount of sulphuric acid may be detrimental to the nitration process. (Nitration by a periodic (discontinuous) method may cause ignition in the nitrator due to the fact that... 

Continuous analytical methods (amperometric and UV-absorption methods) are advantageous. However, sometimes only discontinuous methods (titrimetric and some photometric methods) are available due to expense. In such cases it is important to measure immediately after sampling to avoid the decay of ozone and in the case of liquid ozone to avoid degassing. Discontinuous photometric methods requiring the addition of chemicals to the sample can be converted to a continuous method by combination with flow injection analysis (FIA). This analytical technique requires instrumentation and is not easy to handle. 

One of the features of the method is its lower temperature as compared with the former Bofors discontinuous method which required a temperature up to 140°C at the last stage of nitration. 

The methods in use for the assay of enzymatic activities may be divided into three groups. These will be referred to as the continuous, coupled, and discontinuous methods (see Table 1.1). 

Not all assays require a separation step, and this fact may be used to develop a classification scheme for assay methods. Assays that require no separation have been grouped under the heading continuous assay methods, while discontinuous methods incorporate those that do. 

Gosal et al., 2004). It was claimed that the log discontinuity method most closely reflects the expected percolation threshold behavior. 

Figure 2. Conversion-time curves for MA, discontinuous method...

Maceration has no real advantages over percolation and consists simply in placing the powdered plant sample in any shaped glass or stainless steel container that is stoppered and in contact with the solvent, in order to allow penetration mto the cellular structure to dissolve the soluble compounds. The efficiency of this method may be increased by occasionally shaking the container or by using a mechanical or magnetic stirrer to allow homogenization of the final solution and saturation of the solvent. It is a discontinuous method, and the solvent should be renewed until the plant material is exhausted. This requires occasional filtration steps that may produce loss of solvent, metabo-... 

FRACOD utilizes the Displacement Discontinuity Method (DDM) principles. It was designed to simulate fracture propagation and interaction of multiple fractures in rock masses. 

Abstract The Ratio of Crack Opening Dependency (RCOD) was proposed as a new index to simultaneously evaluate the mechanical and hydraulic properties of cracked structure which contains many open cracks within. The RCOD is an index which is defined as the ratio of total amount of crack opening and the total deformation of cracked structure. The efficiency of RCOD as an index to evaluate the coupled problem was numerically analyzed by applying SCDDM (stress compensation-displacement discontinuity method) to the two dimensional multi crack model. It was shown that RCOD is an useful index which can directly evaluate the deformability and the permeability of the cracked structure without any parameters such as stresses or crack size. The possibility of application of RCOD to the field measurements was also discussed. 

Homogenization analysis of multi joint set problem by the Stress Compensation-Displacement Discontinuity Method (SC-DDM) (1st Report)-, Shigen-to-sozai, 117(11), pp.251-257. 

This is a discontinuous method necessitating the preparation of a great number of samples, cured at various values of temperature and time so as to be able to obtain a law expressed in terms of temperature and time. The principle of the reference temperature or of the reference time was used many times by various authors, and considered as the basis of their method. A modem method of calculation was used at that time, in spite of the fact that an analytical solution exists for the profile of temperatme developed through the thickness of the sample when heated in the mold. 

During the measurement, the air tanperature and the water activity are kept constant until the moisture content of the sample attains the constant equilibrium value. The air may be circulated (dynamic methods) or stagnant (static). The material weight may be registered continuously (continuous methods) or discontinuously (discontinuous methods). 

From the reference, exposure step is performed with rolling motion, but other steps are still done by manual or discontinuous method. For a perfectly continuous system, the photoresist coating and developing process need to be automated. 

The basic TA methods reveal changes in the state of the sample by measuring its single property while the differential TA methods are those in which the measured quantity is the difference between that for the test sample and that for the reference material. Furthermore we can distinguish simultaneous, complementary, coupled and discontinuous methods of thermal analysis. The basic TA methods can be classified into several groups according to the type of measured property, such as methods connected with a change of [9] ... 

In the measurement of pulmonary perfusion, Ga-labeled albumin microspheres have been used extensively [79]. Pulmonary perfusion involves vascular injection of labeled microspheres sized such that they will be mechanically trapped by the first capillary bed they encounter [80]. Previously, a commercial albumin microsphere kit (3M Instant Microspheres) was used in the preparation of Ga microspheres however, this product has been discontinued. Methods were developed to radiolabel macroaggregated human serum albumin (HSA) with Ga using a lyophilized Technescan MAA kit (Mallinckrodt Inc.) [25,33]. 

The older discontinuous method with separate spinning, uses circular spinnerets with the number of orifices up to 150. The spinning speed is 400-600 m/min. New procedures use the so-called compact plant with... 

Heidemann et al also presented a discontinuous method to calculate spinodal curves and critical points using two different versions of the Sanchez-Lacombe equation of state and PC-SAFT. Moreover, Krenz and Heidemann applied the modified Sanchez-Lacombe equation of state to calculate the phase behaviour of polydisperse polymer blends in hydrocarbons. In this analysis the polymer samples were represented by 100 pseudo-components. Taimoori and Panayiotou developed a lattice-fluid model incorporating the classical quasi-chemical approach and applied the model in the framework of continuous thermodynamics to polydisperse polymer solutions and mixtures. The polydispersity of the polymers was expressed by the Wesslau distribution. 

In the discontinuous method only chopped glass is used. High and low shear stresses are developed in this compounding technique, depending on how the glass fiber is blended. 

Many modifications of the two just described methods have been reported in the literature. The main goals of these are (i) to reduce the amoimt of reagents employed, (ii) to increase the sample throughput, (iii) to increase the efficiency of the oxidation step, and (iv) to detect new methods. Table 13.2 presents the most relevant discontinuous methods for COD determination. 

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