Types of HPLC pump

There are several different types of HPLC pump available. However, these all fall into two main classes those which deliver mobile phase at a constant pressure, and those that pump at constant flow rates. In the vast majority (almost 90%) of current analytical HPLC work, it is the latter type of pump that is used. However, both types of pump have their place in modern chromatography, as discussed in the following sections. 

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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. 

The usual type of HPLC pump is the so-called short-stroke piston pump. Its general design, although simplified, is shown in Figure 3.1. The mobile phase is diiven by a... 

The advantages of directly interfacing HPLC separation with NMR analyses have so far been limited by the time and amount of material required to obtain various NMR spectra. However, two different types of HPLC interface have been developed for LC-NMR analysis. In stopped-flow techniques, the material of interest is directed into an NMR sample cell within the magnetic field after HPLC separation has occurred, and the pumps are then stopped to allow the necessary NMR experiments to be performed. The second type of... 

The basic equipment for the RP mode is similar to most other types of HPLC. It consists of solvent reservoirs (one to four), a high-pressure pump, a mixing device that can create any combination of binary solvents or higher order... 

Most high-performance liquid chromatography (HPLC) pumps can be used in HOPC. The back pressure rating should be at least several thousand pounds per square inch (a few hundred kg/cm ). A type of pump that does not allow bypassing the pressure transducer or a pulse damper, if it is installed, must not be used. The dead volume should be as small as possible. Pumps with a single plunger are better than those with two plungers. 

A flow scheme for the basic form of ion chromatography is shown in Fig. 7.3, which illustrates the requirements for simple anion analysis. The instrumentation used in IC does not differ significantly from that used in HPLC and the reader is referred to Chapter 8 for details of the types of pump and sample injection system employed. A brief account is given here, however, of the nature of the separator and suppressor columns and of the detectors used in ion chromatography. 

The types of pumps used for HPLC can be divided into two categories constant-pressure pumps (e.g. the inexpensive gas-displacement pump) and the constant-volume type (e.g. the reciprocating and syringe pumps). The most commonly used pumps in HPLC are the single- or multi-head reciprocating type. The former delivers the flow as a series of pulses which must be damped... 

The high pressure continuous reactor consists of five Kenics type in-line static mixers, that were connected in series [3]. Each reactor unit has 27 Kenics elements and dimensions of 19 cm tube length and 3.3 mm inner diameter. Acetonylacetone and 1 % NaOH aqueous solution were pumped into the in-line static mixer reactor using two independent HPLC pumps. The in-line static mixer reactors were immersed in a constant temperature controlled oil bath at 200 °C so that the reaction mixture was heated to the reaction temperature. When the reaction was completed, the fluid was cooled down rapidly in a constant temperature cold bath at 0 °C. At the end of the cooling line, a backpressure regulator was placed to allow experiments to be run at 34 bar. 

The function of the pump in hplc is to pass mobile phase through the column at high pressure and at a controlled flow rate. One class of pump (constant pressure pump) does this by applying a constant pressure to the mobile phase the flow rate through the column is determined by the flow resistance of the column and any other restrictions between the pump and the detector outlet. Another type (constant flow pump), generates a given flow of liquid, so that the pressure developed depends on the flow resistance. 

The earliest form of constant pressure pump in hplc (the coil pump) used pressurised gas from a cylinder to drive mobile phase from a holding coil through the column. This type of pump was used in some of the older hplc instruments, but is now only of historical interest. If you want to know any more about it, there are details in most textbooks. 

Compared to syringe type or reciprocating pumps, pneumatic amplifier pumps are very cheap. They tend to be rather difficult to dismantle for repairs, and some types are very noisy in operation. Because they do not provide a constant flow of mobile phase, they are not used much in analytical hplc. They can, however, operate at high pressures and flow rates and so are used mainly for packing columns, where high pressures are needed and variations in the flow rate through the column do not matter. 

Two types of constant flow pump have been used in hplc. Fig. 2.2c shows a syringe type pump. 

Air bubbles are the nasties in HPLC work. They cause the same type of troubles as with wet-column chromatography, and you just don t want them. So there s usually a bubble trap (Fig. 112) before the eluent reaches the pump. This device is quite simple, really. Bubbles in the eluent stream rise... 

A second approach to on-line SPE is to use an SPE extraction column that can be used for hundreds of samples. In the simplest of systems, two pumps (either HPLC systems or stand-alone pumps) are connected to an extraction column and an analytical column via 6 or 10 ports, and these are further linked to an MS system. The pump that is connected in-line with the autosampler loads the sample under high flow rate (3 to 5mL/min). The large molecules from the matrix are not retained by the SPE sorbent and are diverted to waste. The analytes of interest are retained by the sorbent. The valve then switches so that the second pump with the elution solvent is now in-line with the SPE column and elutes the analytes onto the analytical column for HPLC/MS analysis. This type of system has proved useful for the analysis of small molecules in a variety of sample matrices such as plasma and urine. While it is relatively straightforward to plumb this type of system with components already in the laboratory, commercial systems are available from such companies... 

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