Gradient programming temperature

Further, the ability to fit retentions as a function of this or that system p2irameter (csist as hypothetical ) provides the means of computer optimization, via window diagrams, not only of the mobile phase but, in addition, the column temperature, gradient programs, stnd so forth (61,62). 

Elution Isocratic Gradient (programmed temperature, chromathermography, programmed flow)... 

Since the column temperature controls both the overall flow rate and the retentions of the individual compounds, a programmed temperature gradient can be used to shorten the CEC run times and optimize the selectivity [151]. 

Although an optimum temperature profile may be specified from theoretical calculations, it may not be possible to achieve in practice. The maximum temperature which can be used is usually determined by the materials of reactor construction or the durability of a catalyst. Also, steep axial temperature gradients cannot be realised unless heat transfer rates are high. If heat transfer is poor and the overall process is exothermic, temperature programming of a single reactor may be impossible the reactor becomes virtually adiabatic. In cases such as these, staged reactors (discussed elsewhere in this volume) with intercoolers may be used as a compromise. 

HPLC column and conditions column packing RP-8 or RP-18 (10 mm) temperature ambient mobile phase acetonitrile-water gradient program from 30% acetonitrile to 60% in 15 min 5 min isocratic flow rate 1.5 mL/min. 

Because the thermal diffusivity of SC water is comparable to that of many high quality insulation materials, gross radial temperature gradients can easily exist in a flow reactor. As shown in Figure 2, radial temperature gradients within the annular flow reactor are negligible. A computer program, which accurately accounts for the effects of the various fluid (solvent, solvent and solute, air) compressibilities on flow measurements, calculates mass and elemental balances for each experiment. A typical experiment evidences mass and elemental balances of 1.00+0.05. 

Another complication may arise if we choose to vary the selectivity of a gradient program in LC by varying more than one parameter at the same time. For example, the concentration of two organic modifiers may be varied independently in RPLC (so-called ternary gradients) or both the mobile phase composition and the temperature may be programmed. 

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