Changeover phase

What this drive towards increased use of process analytics has meant for the pharmaceutical business is a complete rethink of the way assays are done. In many cases the analytical systems need to be added on to existing plant and equipment, and this retrofitting can be technically difficult and expensive to install. Following development of a process assay, there is a changeover phase, during which implementation and optimisation of the assay takes place. However, laboratory analysis will still be done until the new assay has been fully validated. When the assay is fully converted to a process one, it may then be handed over from the analytical group to engineering, or even to maintenance when it becomes fully routine. 

Figure 14.41 The laser welding process. Parts are irradiated with laser energy in phase I, causing heating and melting in the joint interface. The laser beam is switched off in phase II, the shifting or changeover phase, and parts are brought together. In phase III, pressure is applied as the melt layer cools and solidifies.

Reverse phase chromatography is finding increasing use in modern LC. For example, steroids (42) and fat soluble vitamins (43) are appropriately separated by this mode. Reverse phase with a chemically bonded stationary phase is popular because mobile phase conditions can be quickly found which produce reasonable retention. (In reverse phase LC the mobile phase is typically a water-organic solvent mixture.) Rapid solvent changeover also allows easy operation in gradient elution. Many examples of reverse phase separations can be found in the literature of the various instrument companies. 

There are two general types of multidimensional chromatography separation schemes those in which the effluent from one column flows directly on to a second column at some time during the experiment, and those in which some type of trap exists between the two columns to decouple them (off-line mode). The purpose of a trap is often to allow collection of a fixed eluate volume to reconcentrate the analyte zone prior to the second separation step, or to allow a changeover from one solvent system to another. The use of offline multidimensional techniques (conventional sample cleanup) with incompatible mobile phases, is common in the literature, and replacing these procedures with automated on-line multidimensional separations will require continuous development efforts. 

Operation and maintenance (O M) costs for the hquid-phase system are based on 0.08/kWh hour power, 10/hr labor for 1 hr/day, 360 annual days of operation, influent contaminant concentrations of 1 mg/Uter, 5% absorption/weight, 1.00/lb carbon, and a 5-year system life at 8% interest. O M costs for the vapor-phase system are based on a >99% removal of aU VOCs from water with an influent concentration of 1 mg/liter, 75 1 water to air ratio (volume based), 5% absorbency, 10.00/hr operator, 40 hr/year changeover time, no power, no freight, 5-year system life at 8% interest, 5% capital for maintenance, and 1.00/lb regeneration or replacement carbon. 

The electrical conductivity of CoOP as a function of temperature is shown in Figure 6. Above room temperature the compound exhibits metallic behaviour but coincidental with the development of the superstructure the conductivity falls rapidly with decreasing temperature. Below 250 K CoOp behaves as a semiconductor with an activation energy of meV.74 The conduction has been shown to be frequency dependent below 250 K.75 Thermopower studies have also clearly demonstrated the changeover from metallic behaviour above 300 K. to semiconductor behaviour below 250 K.72 The behaviour of ZnOP is very similar to that of CoOp, with the phase transition from the Cccm to Pccn space group occurring at 278 K. Superstructure formation is complete by about 260 K.77... 

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