Mobile phases organic solvent

In GPC, the solvent in which the standards and sample are dissolved should be identical to the mobile-phase solvent in which the analysis will be performed. In most cases filtration is the only step needed to prepare the mobile phase. Organic solvents should be vacuum filtered through a 0.45-pm fluorocarbon filter, while acetate-type filters are used with aqueous mobile phases. In some cases mobile-phase additives are required. When polar solvents such as N,N-dimethyformamide, N,N-dimethylacetamide, and -methyl pyrrolidone are used to analyze polar polymers such as poly-... 

Different mobile phase organic solvents have different selectivity for neutral, acidic, and basic compounds. Therefore, different mobile phase organic solvents are tested as modifiers during method development. In addition, mobile phase buffer pH affects selectivity of acidic and basic compounds. Therefore, different buffer pHs are investigated during method development for acidic and basic compounds. 

Once separation conditions are selected, column, mobile phase organic solvent, and buffer are known. However, column dimension, flow rate, column temperature, mobile phase organic solvent gradient range and gradient time, and buffer pH need to be optimized for better resolution, robustness, and shorter run time. If necessary, buffer concentration needs to be optimized or triethylamine (TEA) needs to be added for better resolution or tailing factor. 

For analysis of basic compounds, silica gel which has been sprayed with a solution of KOH in methanol, may be used. Treating the plate with base ensures that basic compounds chromatograph as their free bases rather than as their salts. The salts of the amines have very low mobility in organic solvent-based mobile phases since basic compounds tend to interact strongly with silanol groups on the surface of the silica the presence of KOH in the stationary phase suppresses this interaction. 

Column packing materials such as silica gel contain a large amount of water, and separation involves partition between an immobilized aqueous phase in the gel and a mobile, often organic, solvent flowing through the column. Usually materials elute sooner when they are more soluble in the mobile phase than in the aqueous phase. These methods are closely related to perfusion chromatography, which is described in Section 2. 

In each separation, the toroidal coil was first entirely filled with a stationary phase (either the upper or the lower phase), and a sample solution was injected into the coil. Next, the mobile phase (organic phase) was pumped into the column while the column was rotated at the desired rate. The effluent from the outlet of the column was collected in test tubes at a rate of 0.2 mL/tube, and at a flow rate of 0.1 mL/min. After the desired peaks eluted, the centrifuge run was terminated and the column contents were fractionated into test tubes at 0.5 mIVtube by eluting the column with the solvent initially used as the stationary phase, at a flow rate of 0.25 mL/min. 

Mobile phase composition The same experiments are performed on the same plates using the same chamber system and environmental conditions changing the mobile phase composition. Analytical performance parameters Rf, / 5, precision, lowest detectable quantity Sample Model A and B or C. %-nonpolar 5% (rel) (normal-phase) or polar [preverse-phase] organic solvent in binary eluent system... 

Because of the stronger hydrophobic interaction of proteins with the stationary phase, organic solvents are used for RPC elution. Elution in HIC occurs by decreasing the salt concentration in the mobile phase. 

Organic Solvent/H20 Mobile-Phase Compositions Having Approximately Equal Solvent Strength... 

The most common mobile phase for supercritical fluid chromatography is CO2. Its low critical temperature, 31 °C, and critical pressure, 72.9 atm, are relatively easy to achieve and maintain. Although supercritical CO2 is a good solvent for nonpolar organics, it is less useful for polar solutes. The addition of an organic modifier, such as methanol, improves the mobile phase s elution strength. Other common mobile phases and their critical temperatures and pressures are listed in Table 12.7. 

In reversed-pViase chromatography (RPC), the mobile phase modulator is typically a water-miscible organic solvent, and the stationary phase is a hydrophobic adsorbent. In this case, the logarithm of solute retention factor is commonly found to be linearly related to the volume fraction of the organic solvent. 

The development of micellar liquid chromatography and accumulation of numerous experimental data have given rise to the theory of chromatographic retention and optimization methods of mobile phase composition. This task has had some problems because the presence of micelles in mobile phase and its modification by organic solvent provides a great variety of solutes interactions. 

---