HPLC pumps operating principles

High-performance liquid chromatography (HPLC) is a versatile analytical technique using sophisticated equipment refined over several decades. An in-depth understanding of the working principles and trends is useful for more effective application of the technique. This chapter provides the reader with a concise overview of HPLC instrumentation, operating principles, recent advances, and modern trends. The focus is on the analytical scale HPLC systems and modules (pump, injector, and detectors). System dwell volume... 

The operating principles of three types of hplc pump are described, together with their advantages and limitations. Techniques for the production of solvent gradients and for the introduction of samples are considered. 

This chapter presents an overview of current trends in high-pressure liquid chromatography (HPLC) instrumentation focusing on recent advances and features relevant to pharmaceutical analysis. Operating principles of HPLC modules (pump, detectors, autosampler) are discussed with future trends. 

Today s HPLC pumps have sophisticated designs honed by decades of incremental improvements. They are also more reliable and easier to maintain than their predecessors. Short seal life and check valve malfunctioning seen in the early models are no longer problems. In this section, the principle of pump operation is described with an emphasis on advances leading to higher reliability and performance. A discussion of system dwell volume is included. 

The HPLC column operates in a similar fashion. The principle of like attracting like still holds. In this case, our nonpolar layer happens to be a moist, very fine, bonded-phase solid packing material tightly packed in the column. Polar solvent pumped through the column, our mobile phase, serves as the second immiscible phase. If we dissolve our purple dye in the mobile phase, then inject the solution into the flow from the pump to the column, our two compounds will again partition between the two phases. The more non-... 

This chapter provides an overview of modern HPLC equipment, including the operating principles and trends of pumps, injectors, detectors, data systems, and specialized applications systems. System dwell volume and instrumental bandwidth are discussed, with their impacts on shorter and smaller diameter column applications. The most important performance characteristics are flow precision and compositional accuracy for the pump, sampling precision and carryover for the autosampler, and sensitivity for the detector. Manufacturers and selection criteria for HPLC equipment are reviewed. 

Pump type and mixing volume To some degree, all modern (U)HPLC pumps allow you to realize an overall GDV of 250 )il or less - getting much below 100 pi of GDV, however, is still a major challenge. Due to their operation principle, high-pressure gradient (HPG)pumps have an inherent advantage with respect to GDV... 

The instruments for polymer HPLC except for the columns (Section 16.8.1) and for some detectors are in principle the same as for the HPLC of small molecules. Due to sensitivity of particular detectors to the pressure variations (Section 16.9.1) the pumping systems should be equipped with the efficient dampeners to suppress the rest pulsation of pressure and flow rate of mobile phase. In most methods of polymer HPLC, and especially in SEC, the retention volume of sample (fraction) is the parameter of the same importance as the sample concentration. The conventional volumeters— siphons, drop counters, heat pulse counters—do not exhibit necessary robustness and precision [270]. Therefore the timescale is utilized and the eluent flow rate has to be very constant even when rather viscous samples are introduced into column. The problems with the constant eluent flow rate may be caused by the poor resettability of some pumping systems. Therefore, it is advisable to carefully check the actual flow rate after each restarting of instrument and in the course of the long-time experiments. A continuous operation— 24h a day and 7 days a week—is advisable for the high-precision SEC measurements. THE or other eluent is continuously distilled and recycled. 

The differences in objective and principle between HPLC and FI separations bring major dissimilarities in the related equipments. The FI flow systems produce much less flow impedance during operation, even when packed columns are implemented. Columns are much shorter, and packing materials are much coarser when they are used to serve FI separation purposes. This in turn substantially lowers the requirement to withstand high pressures for the valves and pumps of a FI system, so that high pressure pumps such as those used in HPLC are not necessaiy. On the other hand, the high versatility of FI often demands multi-functional valves, and multi-channel pumps. These differences may be better understood after comparing the related instrumentation described in Chapter 2 to standard HPLC equipment. 

Compared to other high-throughput systems in this parallel HPLC device, the use of a flow control unit with only one pumping system is a decisive factor. This setup guarantees stabilized flow in an extensible number of simultaneously operated separation columns and thus, in principle, can be combined with any other sophisticated column switching and detection system. A specific version of this instrument was adapted to preparative fractionation and purification of natural product extracts by... 

Ion chromatography (IC) has cemented its position as an integral part of analytical chemistty for the analysis of inorganic and biological ion analysis. IC operates on a principle similar to that of HPLC (a pump, injector, colmnn, and detector), but the main difference is that the entire flow path is constructed with a metal-free material. The principle... 

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