Mobile phase solvents used

Microwave extraction realized at 120 °C for 30 min with Hexane -Acetone (3 2 V/V) as the extraction solvent was identified as the most effective extraction procedure for isolation of TPH from biotic matrices. The aim of this research is to develop a silica gel and alumina fractionation procedure for plant sample extraction. Column chromatography with two solvents (chloroform and hexane dichloromethane) as a mobile phase were used for clean-up of extract. In this research the efficiency of recovery received from chloroform as a mobile phase. 

The organic solvent used to elute the compound must be adequately strong (polar for the adsorbent silica gel) and a good solvent for the component. Absolute methanol should be avoided as a siugle solvent because silica gel itself and some of its common impurities (Fe, Na, SO4) are soluble iu this solvent and will contaminate the isolated material. Solvent containing less than 30% methanol is recommended, or ethanol, acetone, chloroform, dichloromethane, or the mobile phase originally used for PLC are other frequently nsed choices for solnte recovery. Water is not recommended because it is so difficult to remove by evaporation during the concentration step (removal by lyophilization is necessary). A formula that has been used to calculate the volume of solvent needed when the PLC mobile phase is chosen for elution is ... 

The popularity of reversed-phase liquid chromatography (RPC) is easily explained by its unmatched simplicity, versatility and scope [15,22,50,52,71,149,288-290]. Neutral and ionic solutes can be separated simultaneously and the rapid equilibration of the stationary phase with changes in mobile phase composition allows gradient elution techniques to be used routinely. Secondary chemical equilibria, such as ion suppression, ion-pair formation, metal complexatlon, and micelle formation are easily exploited in RPC to optimize separation selectivity and to augment changes availaple from varying the mobile phase solvent composition. Retention in RPC, at least in the accepted ideal sense, occurs by non-specific hydrophobic interactions of the solute with the... 

If the performance of a column is no longer satisfactory it can sometimes be reconditioned by washing with a suitable solvent, or series of solvents. Some bonded phase columns, C-18 for instance, tend to collect non-polar impurities, which can sometimes be removed by washing the column with a non-polar solvent, eg heptane. Assuming the mobile phase normally used with the column is CH3OH/H2O 50 50, we cannot wash directly with heptane because of miscibility problems, we have to get to heptane via a miscible solvent or series of solvents. 

Solvent strength refers to the ability of a particular mobile phase (solvent) to elute mixture components. For example, if use of a particular solvent results in short retention times for mixture components, the solvent is strong. If use of a solvent increases retention times, it is a weak solvent. 

Solute-property detectors. They critically respond to a particular physical or chemical characteristic of the solute (in question), which should be ideally and absolutely independent of the mobile-phase being used. But complete independence of the mobile-phase is hardly to be seen, however, signal discrimination is good enough to enable distinctly measurable experimental procedures with solvent changes, such as gradient-elution. 

Buffered mobile phases are used and the proportions of polar solvents (e.g. methanol, tetrahydrofuran) depend upon the type of derivative employed. Gradient elution is required for the resolution of complex mixtures and analysis times are less than 1 h. Ultraviolet, fluorescence or electrochemical detectors are used depending upon the nature of the amino acid derivatives. 

Additional modes of HPTC include normal phase, where the stationary phase is relatively polar and the mobile phase is relatively nonpolar. Silica, diol, cyano, or amino bonded phases are typically used as the stationary phase and hexane (weak solvent) in combination with ethyl acetate, propanol, or butanol (strong solvent) as the mobile phase. The retention and separation of solutes are achieved through adsorp-tion/desorption. Normal phase systems usually show better selectivity for positional isomers and can provide orthogonal selectivity compared with classical RPLC. Hydrophilic interaction chromatography (HILIC), first reported by Alpert in 1990, is potentially another viable approach for developing separations that are orthogonal to RPLC. In the HILIC mode, an aqueous-organic mobile phase is used with a polar stationary phase to provide normal phase retention behavior. Typical stationary phases include silica, diol, or amino phases. Diluted acid or a buffer usually is needed in the mobile phase to control the pH and ensure the reproducibility of retention times. The use of HILIC is currently limited to the separation of very polar small molecules. Examples of applications... 

Note After Experiment 4, one should switch the 1000 psi back-pressure device with a validated Cl8 column and adequately equilibrate the column with the appropriate mobile phase required for the subsequent experiment. The mobile phase solvents are usually percentages of methanol and water, depending on the chromatographic requirements for eluting the standard components that are used. 

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