Columns multiple

Examination of possible systems for boron isotope separation resulted in the selection of the multistage exchange-distillation of boron trifluoride—dimethyl ether complex, BF3 -0(CH3 )2, as a method for B production (21,22). Isotope fractionation in this process is achieved by the distillation of the complex at reduced pressure, ie, 20 kPa (150 torr), in a tapered cascade of multiplate columns. Although the process involves reflux by evaporation and condensation, the isotope separation is a result of exchange between the Hquid and gaseous phases. 

Figures 13.25-13.28 show the ultrahigh resolution separations in chloroform of polystyrene standards, polytetramethylene glycol, urethanes and isocyanates, and epoxy resins, respectively. Multiple column sets of anywhere from two to six columns in series have been used for well over a year with no apparent loss of efficiency. The 500- and 10 -A gels can easily tolerate 15,000 psi or more. In fact, the limiting factor in the number of columns that can be used in series is generally the pump or injector in the FIPLC system. A pump capable of 10,000 psi operation should allow the use of a column bank of 10-12 50-cm columns with a total plate count of 500,000 or more.

The first reported case of timesharing for a mass spectrometer9 involved the design of an Ionspray interface with multiple sprayers to support the analysis of effluents from multiple columns. This approach led to the development of a multiplexed electrospray interface (MUX)10 using an LC/MS interface and multiple (identical) sprayers linked to a HPLC system and a spinning screen to allow the output of only a single sprayer to enter the MS (Figure 4.5). The injections of the HPLC systems... 

Once it was realized that multiple columns in the first SEC really did not offer cmy advantage in terms of greater injection amounts because of increased dilution in the columns, smaller injections and less columns reduced emalysis times 50% with no loss in sensitivity. For the analyses shown in Figure 8, only three columns were used in the first SEC and three in the second. With this system the first analysis by both SBC instruments required a total of 30 minutes and subsequent analyses of the same sample eibout 15 minutes each. However, despite these significant reductions in analysis times in comparison to the initial work, complete analysis of even one complex polymer required many cross fractionations and generated much data. 

The different techniques used in solid-phase glycopeptide synthesis, such as the low-cost plastic syringe technique or the multiple column technique, and also one type of fully automated synthesis, have been reviewed by Peters et al.1181... 

Don t use multiple columns, tables, or charts within your document. Instead of tabs, indent text using spaces. 

S. Peter, T. Bielefeldt, M. Meldal, K. Bock, and H. Paulsen, Multiple-column solid-phase glycopeptide synthesis, J. Chem. Soc. Perkin Trans 7 1163 (1992). 

SC (simultaneous correction) method. The MESH equations are reduced to a set of N(2C +1) nonlinear equations in the mass flow rates of liquid components ltJ and vapor components and the temperatures 2J. The enthalpies and equilibrium constants Kg are determined by the primary variables lijt vtj, and Tf. The nonlinear equations are solved by the Newton-Raphson method. A convergence criterion is made up of deviations from material, equilibrium, and enthalpy balances simultaneously, and corrections for the next iterations are made automatically. The method is applicable to distillation, absorption and stripping in single and multiple columns. The calculation flowsketch is in Figure 13.19. A brief description of the method also will be given. The availability of computer programs in the open literature was cited earlier in this section. 

Another important experimental consideration is the potential for nonequilibrium sorption in short experimental columns. In particular, a drawback of using spatial data is that model calibration of a sorption rate constant is more difficult. For example, Khandelwal and Rabideau (in press) showed that multiple combinations of Kj and a can be used to generate equivalent predictions for a single-time contaminant spatial distribution. As discussed below, this concern can be addressed by using multiple columns operated for different durations. 

As discussed above for low-permeability systems, the analysis of spatial contaminant distributions is an appealing strategy for shortening the duration of column experiments. Again, the use of multiple columns operated over... 

Drinking water (CDDs) Addition of 13C-labeled CDD internal standards extraction with organic solvent volume reduction clean-up on multiple columns of silica gel/basic silica/acidic silica, AgN03-siiica/basic alumina, and HPLC HRGC/LRMS (SIM) HRGC/MS/MS (SIM) No data No data McCurvin et al. 1989... 

S. R. Lowry, G. L. Ritter, H. B. Woodruff, and T. L. Isenhour, Selecting liquid phases for multiple column gas chromatography from their eigenvector projections, J. Chromatogr. Sci., 14 126 (1976). 

Multiple column switching has been made possible by the construction of a cyclic CE microstructure in which four channels that are 20 mm in length are arranged to form a square, as illustrated in Figure 8.20.62 Two channels at each corner connect the loop to external reservoirs filled with separation buffer. Platinum electrodes are inserted into the reservoirs for the application of high voltages. One side of the device has a volume-defined injection scheme incorporated into it. The overall technique is called synchronized cyclic capillary electrophoresis.63... 

A similar approach with multiple columns operating as automated multi-dimensional LC has also been reported by Machtejevas et al. for peptides from human blood filtrate [101],... 

Much of the benefit of countercurrent operation, without the problems associated with circulation of the adsorbent, can be achieved by using a multiple-column fixed-bed system with an appropriate sequence of column switching, designed to simulate a counterflow system. The general scheme is illustrated in Fig. 13. Such systems are widely used in wastewater treatment,... 

The main advantages of batch distillation over a continuous distillation lie in the use of a single column as opposed to multiple columns and its flexible operation. 

Russell s method is one of the methods used in the MULTIFRAC option for multiple columns in ASPENPlus and is the column method in HYS1M of Hyprotech of Calgary, Alberta. Russell s method as written by Richard Russell is in the PD+Plus system available from Deer-haven Technical Software in Deer haven, Massachusetts. The HYSIM and PD+Plus versions of Russell s method have been found to work well for refinery fractionators with sidestrippers and other similar columns including columns for which a version of Boston s method failed. 

Although GC has become a mature analytical technique, improvements are still being made. New and better OT columns are becoming available so that their use has expanded, requiring new and better instrument designs. Multiple columns and column switching are becoming popular a series of papers on the subject of multidimensional GC describes the current developments.30... 

Since any single column packing has a limited range, it is often necessary to perform SEC with multiple columns in series. This procedure extends the molecular weight range over which separations can be effected. 

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