Pumps and Sample Injection System

Pumps The two major functions of the pump in a modem HPLC are, namely  

Importantly, in a constant-pressure pump the flow rate will change if the flow resistance changes. Whereas in the constant flow pumps the changes in flow resistance are compensated duly by a change of pressure. Therefore, it is always advisable to use constant flow pump in HPLC determinations. 

The pump is a very delicate and sensitive part of HPLC unit therefore, all buffer solutions should be removed carefully after use either by pumping water (HPLC-grade) or an appropriate solvent (HPLC-grade) for several minutes. 

Sample Injection System There are in all three different modes of sample injection system that are used in HPLC, namely  

Therefore, it is always preferred for most quantitative work by virtue of its very high degree of precision and accuracy. 

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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. 

High Performance Liquid Chromatography (HPLC) (Chapter 30) gives an elaborate discussion of theoretical aspects. Instrumentation encompasses the various important components e.g., solvent reservoir and degassing system pressure, flow and temperature pumps and sample injection system ... 

The essential components of the instrumentation are a solvent reservoir, a solvent delivery system (pump), sample injection system, packed columns, a detector(s), and a data processing system. 

Fluidic approaches move samples, reagents, and eluents from place to place entirely through a system of pumps, valves, and tubing. Fluidic methodology from the field of flow injection (FI) analysis has been adapted to the needs of automated radiochemistry. In its original form, FI used a multichannel peristaltic pump and an injection valve in a continuous forward flow paradigm to mix the sample with reagents and... 

The chromatographic equipment which is responsible for the separation includes the pump, and in many systems a column oven. The parameters which affect the separation are the flow rate, the solvent composition and the LC gradients. Many different software packages are available which allow completely unattended automatic chromatography. Such systems also include control of the sample injection process. 

Disposable pTAS will be ideal for medical use [14]. However, the high fabrication cost of sophisticated pTAS including micropumps and microvalves is a real problem. One of the basic components of medical pTAS taking this into account is illustrated in Fig. 2. A detector cell consists of micro sensors and a 3-way microvalve is placed at the sample inlet. Flow is controlled by a suction pump and an injection pump connected to the detector cell. The calibration solution flow is also controlled by an individual pump and a 3-way valve. In this system, only sample flow reaches the detector cell. The upper parts of the system are free from contamination and corrosion so that they can be reused many times, while the detector cell has to be disposed of. To realize this system, a 3-way microvalve which can handle whole blood is indispensable. A separable channel type microvalve whose channel part is disposable while actuator part is reusable is useful for the 3-way microvalve of the detector cell [15]. Mechanically fixed stack structures including disposable parts are useful in many medical pTAS. 

A typical block scheme of gel chromatographic apparatus is shown in Fig. 4.6.4. The mobile phase flows from the solvent container, C, into degassing unit, D, and through filters, F, reaches the pumping system, P, which transports it via the pulse damper, PD, and the sample injecting system, I, into the column, CO. The effluent from the column enters the detector, DE, and flows through the volumeter, V, into the fraction collector, F. 

CapOlatity-driven stop valve and sample injection switch Microflow switch Multichannel micro liquid dosing system Multichannel microswitch pumping... 

Ion chromatography consists of the following parts (1) eluent generation system, (2) pump system, (3) sample injection system, (4) column system, (5) thermostat chamber, (6) suppressor, (7) detector and data handling system. 

The testing system consisted of a carrier, a syringe pump, a sample injection valve, and a laboratoiy-built flow-through electrochemical cell (Figure 8). The cell was constructed by sandwiching an SPE between a plastic base and a plastic cover outfitted with inlet and outlet holes. A Teflon gasket with a flow channel was mounted between the SPE and the cover to form a flow cell, in which the SPE was exposed to the cell for the electrochemical detection. 

The simplest setup consists of a peristaltic pump, an injection valve, the immunoreactor, and a detector. For special purposes multichannel pumps and valve switching systems have been developed. Sample and all reagents are injected into a flowing stream and transported to the immunoreactor where binding to the immobilized antibodies (or antigens, respectively) takes place. Detection is carried out either... 

An important component of many bio- or chemical Lab-on-a-Chip devices is the microfluidic injection system, the precise control of the size and concentration of the dispensed sample in the microfluidic injection system determines the performance of these Lab-on-a-Chip devices. Two methods are commonly adopted in microfluidic injection systems electrokinetic injection and pressure injection. Pressure driven injections have the advantage that precise voltage control is not necessary and sample injections of uniform composition can be obtained. However, pressure injections require a means to transport or pump the sample that is dissolved in a liquid. Switchahle valves which direct the flow into a desired direction can achieve flow control. These valves are difficult to integrate into microfluidic devices, so the kinetic injection system prevails within the microchip [2]. 

In its simplest form, FI-ICP-MS consists of a series of pumps and an injection valve preceding the sample introduction system of the ICP mass spectrometer. A typical manifold used for microsampling is shown in Figure 17.5. 

The linear displacement apparatus shown in Fig. 1 consisted of the injection and sample gathering system, the core holder, and the pressure sensing system. An ISCO Model 312 metering pump was used to inject fluids into the core at a constant flow rate. Effluent stream samples were collected in 9-ml test tubes with a Gilson Model FC-80 Micro Fractionator. 

Aschematic diagram of the flow injection system used by Anderson [126] is shown in Fig. 2.4. An Ismatec model MP13 peristaltic pump was used. Different flow rates were obtained by changing the pump tube diameter, as indicated in the legend to Fig. 2.4. The injection port was a rotary valve [131,170]. The sample volume could be varied between 10 and 1000 pi simply by changing the length of the sample loop. 

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