Solvent delivery

The controller is capable of controlling all aspects of the experisental procedure. The flow rates of the pumps are controlled very precisely the sample is applied automatically to the coluam by the V-7 valve which is also under the control of the controller the coluam can be easily re-equilibrated for the next sample application. Use of the V-7 valve allows the sample to be pumped onto the column at the same flow rate as used during the chromatography. 

To study protein self-association over a wide concentration range, a variable wavelength UV detector is recommended. This allows for the selection of a wavelength to either minimize absorbance at high protein concentrations or to maximize absorbance at low protein concentrations. Several excellent instruments are on the market. We have used the Isco V4 variable wavelength detector successfully. 

The choice of buffer to be used in the large zone SEC experiment is dependent upon several factors. The buffer must be conqpatible with the coluam being used. For example, extremes of pH must be avoided with silica 

Once a buffer is chosen, it is critical that the colusm be fully equilibrated in that buffer. As a rough rule of thumb, pumping two to three column volumes through the coluom will generally achieve proper equilibration. 

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The solvent delivery system must be capable of pumping solvent at a constant, pulse-free flow rate of 0.3 ml/min. Traditionally, SEC pumps have been optimized to operate at 1.0 ml/min. 

Figure 2.12 Schematic representation of an on-line SPE-GC system consisting of three switching valves (VI-V3), two pumps (a solvent-delivery unit (SDU) pump and a syringe pump) and a GC system equipped with a solvent-vapour exit (SVE), an MS instrument detector, a retention gap, a retaining precolumn and an analytical column. Reprinted from Journal of Chromatography, AIIS, A. J. H. Eouter et al, Analysis of microcontaminants in aqueous samples hy fully automated on-line solid-phase extraction-gas chromatography-mass selective detection , pp. 67-83, copyright 1996, with permission from Elsevier Science.

Toluene (J. T. Baker CYCLE-TRAINER solvent delivery kegs) was vigorously purged with argon for 2 hr and then passed through two packed columns of neutral alumina and copper(II) oxide under argon pressure.3... 

Toluene and dichloromethane (CHjCy were purified by a JT Baker Cycle-Tainer Solvent Delivery System. 

The instrument used in this study was an in-house constructed HPGPC composed of a Waters Associates M-6000 solvent delivery system, Waters Associates U6K injector, Varian Instruments fixed... 

HPLC has also been used to determine the residue levels of dinifroaniline herbicides. Pendimethalin was quantified by HPLC under the following conditions apparatus, Spectroflow 400 solvent delivery system. Model 430 gradient former, and Kratos Model 783 with UV absorbance detection at 239 nm column, Cig reversed-phase (25cmx 3.0-mm i.d.) temperature, 40 °C mobile phase, acetonitrile-water (7 3, v/v) flow rate, 1 mL min . ... 

Experimental variables such as temperature, flow rate, sample concentration and mobile phase composition can cause changes in the elution volume of a polymer [439,457,460-464]. Chromatographic measurements made with modem equipment are limited more by the errors in the absolute methods used to characterize the molecular weight of the calibration standards than any errors Inherent in the measurements themselves, since the determination of molecular weights by SEC is not an absolute method and is dependent on calibration [462]. The Influence of temperature on retention in SEC is not very great, since no strong sorptive interactions are involved in the retention mechanism. Temperature differences between the column and solvent delivery... 

Reciprocating-piston pumps deliver a constant flow at si fixed backpressure. At high pressures some minor flow variability ziay arise due to the compressibility of the mobile phase. Soms instruments incorporate a flow controller which provides a fixadi backpressure for the pump to work against, independent of the column backpressure. The influence of pressure fluctuations, solvent compressibility, and solvent viscosity on the volumetrie output of the pump are thereby eliminated. Reciprocating-piston pumps can provide continuous solvent delivery, fast solvent change--... 

The solvent delivery system is one of the most important components of the liquid chromatograph since its performance directly affects retention time reproducibility d detector baseline stability [1,2,39,40]. As well as the pump, other components such as check valves, flow controllers, mixing... 

Solvent delivery system stainless steel columns injection port flow-through detector, recorder. Applications... 

Figure 4.31(b) from Euston and Glatz, A new Hplc Solvent Delivery System, Techn. Note 88-2 (1988) by permission of Hewlett-Packard, Waldbronn, Germany. 

The //PLC system described in this chapter is equipped with 24 parallel columns for liquid chromatography, each with its own sample introduction port and exit port for connection to detectors of choice (UV absorbance and/ or fluorescence). Flow from a binary solvent delivery system is divided evenly across 24 channels and results in 1/24 of the programmed pump flow rate through each column (i.e., total flow of 300 /zL/ min will produce a flow of 12.5 /zL/ min in each column). Samples are introduced to the columns by a multichannel autosampler configured to sample from either 96-or 384-well SBS standard plates. Figure 6.2 depicts a general view of the system. 

If the substance is not listed and no information answering the question of electro-activity can be obtained from the literature, a simple flow-injection experiment using hydrostatic solvent delivery may help to answer the question (see Figure 4-1). 

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