Gradient pumping systems

The criteria used to judge the performance of a low-pressure pump include compositional accuracy, ripple, flow accuracy, and pressure accuracy. Compositional accuracy is tested by following the American Society for Testing and Materials (ASTM) procedure E-19.09.07.5 In this procedure, two bottles of eluent are used, one containing 100% methanol (eluent A) and the other containing methanol with a low concentration of acetone 

Chapter 3 Instrumentation for High-Performance Liquid Chromatography 

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The Type II system comes in two flavors. They vary by the type of gradient pumping system they contain low-pressure mixing or high-pressure mixing. The rest of the system is the same injector, variable detector, and computer-based data acquisition and control. Autosamplers would allow 24-hr operation, but most university research laboratories find graduate students to be less expensive. 

Tolson, D. Organ, A. Shah, A. Development of a High-pressure Gradient Pumping System for Parallel Liquid Chromatography/Mass Spectrometry for the Analysis of Combinatorial Libraries, Rapid Commun. Mass Spectrom. 15, 1244-1249 (2001). 

This active flow control unit is plugged to an isocratic or gradient pumping system. It divides the total pump flow Ftomi into exactly equal split... 

LC/MS(-MS) system equipped with binary gradient pump system, autosampler, column oven (30°C), the respective mass spectrometer with ESI interface, data acquisition and processing system. A UV detector (286 nm) may be used as option, but a UV signal will only be recorded for injection solutions >1 mg/L. 

High-pressure gradient pumping system and a Rheodyne Model 7725 injection valve equipped with a 20-pL internal loop. 

This case serves to point out the importance of maintaining a constant hydraulic gradient on the inside and outside of a slurry wall. This can also become a factor if slurry walls are used with groundwater pumping systems (extraction wells). Then water must be reinjected to maintain a... 

In the pneumatic pumping system, the pressure (and not the flow rate) is maintained constant as variations in chromatographic conditions occur. Thus, a change in mobile phase viscosity (e.g. gradient elution) or column back pressure will result in a change in flow rate for these types of pumps. The gas displacement pump in which a solvent is delivered to the column by gas pressure is an example of such a pneumatic pump. The gas displacement system is among the least expensive pumps available and is found in several low cost instruments. While the pump is nonpulsating and hence, produces low noise levels with the detectors in current use, its flow stability and reproducibility are only adequate. In addition, its upper pressure limit is only 2000 psi which may be too low in certain applications. 

The trench method is applicable only when the water table is relatively shallow, less than 10 to 15 ft below the ground surface. For a deeper water table, the cost of the trench method becomes more expensive than other methods such as pump systems. Another limitation of the trench method is the soil structure. The soil above the water table has to be firm and well aggregated to allow for the trench to be self-supporting. Otherwise, embankment enforcement or screening would be needed. A third limitation is that continuous pumping and skimming is required to maintain a flow gradient towards the trench. Otherwise, the free product will move back and reenter the soil. 

Phase 4 Hyperpolarization occurs before K+ efflux has completely stopped and is followed by a gradual drift towards threshold (pacemaker) potential. This is reflects a Na+ leak, T-type Ca2+ channels and a Na+/Ca2+ pump, which all encourage cations to enter the cell. The slope of your line during phase 4 is altered by sympathetic (increased gradient) and parasympathetic (decreased gradient) nervous system activity. 

The exchange-quenched solution is then injected onto the protein processing system which includes injection loops, protease column(s), a trap column, an analytical column, electronically controlled valves, and isocratic and gradient pumps. 

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