Gradient devices

This is achieved by controlling and changing the flow-rate of both of the pumping systems used. Gradient elution is often necessary for satisfactory separations of complex mixtures. Commercial chromatographs which have gradient devices are summarized in Table 3.3. 

Gradient Devices. Gradient devices can also be divided into two types high pressure and low pressure. In a typical low pressure system (depicted in Figure 9.22), various proportions of up to three solvents are mixed before they enter the high pressure pump. The proportions are regulated by valves that are in turn controlled electronically with microprocessors. 

Drost-Hansen, W. (1981). Gradient device for the study of temperature effects on biological systems. J. Wash. Acad. Sci. 71, 187-201. 

The nanofluidic preconcentration device can be considered an equilibrium gradient device using a steep electric field gradient and an opposing bulk flow to focus analytes [243]. Other equilibrium gradient techniques have also been implemented in microfluidic channels. These techniques include temperatare... 

Figure 21.21. Gradient devices used in liquid chromatography. A Simple mixing device for gradient elution, gradient formed on low-pressure side of pump. Ri is the flow rate of A into the flask. Ra is the flow rate of A + B to column. B Gradient profiles obtained from A. C Schematic for two-pump gradient chromatograph. Gradient formed on high-pressure side of pump.

Push CB through the microfluidic gradient device until you have filled all remaining needle hubs see Note 10). 

Concentration Gradient Generation and Control, Fig. 4 Generation of dynamic nonlinear gradients, (a) Schematic of the microfluidic device. A mixer module was connected to the middle inlet of a three-inlet gradient device that generates nonlinear gradients, (b) Nonlinear... 

Combined experiments require a higher level of sophistication of the sample environment. Many examples can be foimd in the literature, for instance, fast stop-flow cells (99), concentration gradient devices (100), and temperature jump cells (101). In the following sections some techniqne combinations and the implications for sample cell construction are discnssed see also Reference 5. Before treating... 

The gradient device morphology allows a better match to the built-in electric field, allowing a larger area of the device to be the active layer in a number of optoelectronic and photonic applications, thus increasing the amount of electron-hole pairs which can be effectively separated. Synthetic methods used to prepare the gradient structures are listed below. 

Table 3.6 shows the effect of pressure on temperature and pressure on water volume. In going from 0 to 1000 atm (a typical UHPLC pressure drop), the volume of water is reduced by 4% at 40°C. The effect on chromatography due to compression of mobile phase can be seen in gradient devices using two or more pumps to mix components at high pressure. It is important for the pumps to deliver the exact volume accurately otherwise the flow rate and thus retention time could be affected during a... 

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