Solvent gradient systems

Gradient systems let you control flow rate and solvent/buffer changes to improve chromatographic separations. They can be used to sharpen separations and to speed column re-equilibration. A four-solvent gradient system is useful for methods development when equipped with methanol, acetonitrile, ammonium acetate buffer, and formic acid solution. But, many quality control laboratories prefer to use inexpensive isocratic systems that run a constant-composition premixed mobile phase for rapid separations. 

An open tubular capillary was used for the evaluation of the performance of the solvent gradient system. Fluoranthene, added to the mobile phase in the second reservoir served as a fluorescent tracer to indicate the percentage of this solvent constituting the final mobile phase. The time between the beginning of the linear portion of the voltage program and the onset of the increase in measured fluorescence... 

The following solvent gradient system provides optimum results at a flow rate of 1.2 ml/min ... 

In recent years, a new approach by Cong et al. using a thermal gradient instead of a solvent gradient system on the same carbon-based column has demanded... 

Figure 3.3 Solvent gradient systems in HPLC, where P is a pump, M is a mixer, I is an injector,...

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 . ... 

Supercritical fluid chromatography pressure gradient solvent delivery system Pierce Chemicals Life Science Laboratories Ltd Sedgewick Road Luton... 

The rise in popularity of HPLC is due in large part to its high-performance nature and the advantages offered over the older, noninstrumental open-column method described in Chapter 11. Separation and quantitation procedures that require hours and sometimes days with the open-column method can be completed in a matter of minutes, or even seconds, with HPLC. Modern column technology and gradient solvent elution systems, which will be described, have contributed significantly to this advantage in that extremely complex samples can be resolved with ease in a very short time. 

The HPLC gradient system consisted of two pumps for solvent delivery, an injector, a 120 x 4.6 mm Polyspher AA-NA column (Merck, 75°C), a pump for reagenf delivery, a mixing tee with reaction coil, and a fluorescence detector lined to an integrator (Waters). 

RPC with mobile phases containing relatively high concentrations of salts (0.1-0.5M) is occasionally employed for separations of organic acids or bases [67-69], Eqnation 5.7 can often describe the effect of the concentration of organic solvents on the retention in these phase systems, so that Eqnations 5.8 and 5.9 can be principally used for calculation of the retention data in the LC with organic solvent gradients. 

In the literature, isocratic solvent systems are found for monosaccharides, and gradient systems are described for oligosaccharides. Table 3.4 gives some gradient systems for carbohydrate separation Table 3.5 illustrates programs for pulsed amperometric detectors. 

Furfural exhibits high selectivity at elevated temperatures (175° to 250° F.) this characteristic results in the benefits of reduced viscosity and high temperature gradient and permits operation on waxy stocks. At ambient temperatures, kerosenes and gas oils may be extracted. Water in furfural has a bad effect on its extraction efficiency therefore, solvent recovery systems must include dehydration facilities. From its chemical composition aldehyde furfural appears to be unstable. However, when handled in accordance with standard operating procedures, decomposition and polymerization are negligible. 

A flow diagram of an anhydrous phenol solvent extraction plant is shown in Figure 8. Raw distillate is passed through a tower in which it absorbs phenol from the recovery system vapor. The oil is then passed to the treating tower, generally a few sections above the bottom. Anhydrous phenol is introduced at the top of this tower. Phenolic water condensate from the solvent recovery system (about 9.5% phenol) is introduced at the bottom of the tower to effect reflux. A temperature gradient of 10° to 75° F. may be... 

---