The Solvent Pump

The mobile phase must be brought to a constant and fixed temperature (and thus constant density) prior to entering the column and, if the volume flow rate through the column is to be maintained constant, then the pump must deliver a constant mass flow-rate to the column. As the pump is designed to provide a constant volume flow rate, then it must be supplied with solvent at a constant density and its displaced volume must also remain constant. If a precision of 0.10% is required, then the displaced volume of the pump and the solvent density must also be maintained constant to within this level of precision. It is almost impossible to thermostat the pump so the ambient temperature of the pump and solvent reservoir must be controlled, and this means that the temperature of the room in which the apparatus is 

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The maximum and minimum flow rate available from the solvent pump may also, under certain circumstances, determine the minimum or maximum column diameter that can be employed. As a consequence, limits will be placed on the mass sensitivity of the chromatographic system as well as the solvent consumption. Almost all commercially available LC solvent pumps, however, have a flow rate range that will include all optimum flow rates that are likely to be required in analytical chromatography... 

One day, the lead operator gave verbal and written instructions, via a second worker, to the top floor man to pump solvent to 12A blender. The top floor man actually pumped the solvent to 21A blender, as a result of connecting the hose to the 21A blender pipe and not the 12A blender pipe. Consequently the solvent pumped to 21A blender was charged on top of another batch already in 21A blender. The contaririnated batch had to be pumped back into a reactor where the mischarged solvent was removed by the application of vacuum. 

The solvent pump was turned on at t 0 sec. It takes ca. 20 sec for the solvent to reach the flow cell containing the PMMA-Phe sample. A significant reduction in fluorescence intensity signals the arrival of solvent at the PMMA-Phe surface. 

However, it has been mentioned before, and must be bourne in mind, that it is not the pressure capability of the solvent pump that normally determines the maximum pressure that can be employed, but the maximum pressure the whole chromatographic system can tolerate. Although valves have been designed to operate at 10,000 p.s.i., or even higher, their useful lifetime at that pressure is often relatively short, usually as a result of sample contamination scoring the valve seats. For long-term continuous operation the maximum inlet pressure a valve can tolerate is often only about 3000 p.s.i.. 

Flow rate control of the solvent pump was difficult because 0.2 L/h is near the low end of the solvent pump s capacity. 

The ChromSpher Lipids column (250 mm X 4.6-mm ID stainless steel 5 /Am) was purchased from Chrompack (Middelburg, Netherlands) and used as received. Solvent flow was standardized at 1.0 ml/min and run temperatures at 22-23°C. A small cooling fan was used to minimize temperature fluctuations and bubble formation at the solvent pump mixing solenoid. 

Sample injector The sample injector is located between the solvent pump and the HPLC column, and serves to deliver or inject the sample dissolved in solvent onto the column. The most common form of sample injector is the so-called loop-and-valve injector. Sample is injected from a specialized syringe (manually) or delivered by means of an autosampler (automatically) into a small diameter loop. The loop-and-valve injector allows switching by means of a valve between initial delivery of solvent alone to the column (so-called column equilibration), to subsequent delivery of the sample onto the column. 

Modem solvent extraction plants recover over 99.9% of the solvent pumped to the extractor. The solvent recovery system includes solvent and water vapor condensation, solvent-water separation, stripping solvent from water and air effluent streams, as well as heating the solvent prior to reuse in the extractor. 

Fill the solvent pump (A). Close (clockwise) the pump outlet valve (E). 

The solvent programmer is an apparatus that allows the composition of the mobile phase to be changed, in a defined manner, over a defined period of time, and is normally controlled by the chromatograph computer. There are basically two types of gradient programmer, one that mixes the solvents at high pressure, prior to the column and the other that involves solvent mixing that occurs at low pressures, prior to the solvent pump. 

Traditionally maintenance parts are replaced on a time base. For example, an HPLC pump seal every 2 months, a detector s lamp every 3 months or so. This is not economical for the laboratory and not environmentally friendly because frequently a replacement of the parts would not yet be necessary. A better way is to exchange maintenance parts on a usage basis. The user can enter limits for the lamp, the solvent pumped through and the number... 

High molecular weight poly(hexylmethylsilylene), on a 1 gram scale, was reacted with several equivalents of chlorine per chain, in CCI4 solution at -20°C under vacuum. The chlorine colour disappeared instantly. The reaction mixture was allowed to come to room temperature, and the solvent pumped off. To remove the residual CCI4, toluene was condensed in, the product dissolved, and the toluene pumped off and the cycle repeated three times. The product was finally dissolved in toluene and stirred overnight at 110°C under vacuum with freshly distilled sodium. The reaction product was finally terminated with MeLi in diethylether to remove any remaining chlorine, and analyzed by SEC. 

Design of reciprocating pumps. The discussion below is limited to the solvent pumps used for high pressure extraction. In the range of conditions... 

A cooling effect is achieved if the rich solvent is directed through hydraulic turbines to provide part (up to almost 50%) of the solvent pumping energy. Without these turbines, motor or steam driven turbines would be needed and additional shaft work would be added to the system. 

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