Mobility solvents

Choosing a Mobile Phase Several indices have been developed to assist in selecting a mobile phase, the most useful of which is the polarity index. Table 12.3 provides values for the polarity index, P, of several commonly used mobile phases, in which larger values of P correspond to more polar solvents. Mobile phases of intermediate polarity can be fashioned by mixing together two or more of the mobile phases in Table 12.3. For example, a binary mobile phase made by combining solvents A and B has a polarity index, of... 

In classical column chromatography the usual system consisted of a polar adsorbent, or stationary phase, and a nonpolar solvent, mobile phase, such as a hydrocarbon. In practice, the situation is often reversed, in which case the technique is known as reversed-phase Ic. 

This classification is concerned with whether the detector monitors a property of the solute (analyte), e.g. the UV detector, or a change in some property of the solvent (mobile phase) caused by the presence of an analyte, e.g. the refractive index detector. 

The results of TRFSS experiments have shown us that the reverse micellar interior has the effect of limiting solvent mobility [30,31,38 0,42,43] The origin of this immobilization is still unclear. While specific interactions with the surfactant headgroups seem to play a role, the reverse micellar milieu seems more important than a high concentration of ions. 

Figure 6.7 depicts an autosampler employed in a jtPLC system. Figure 6.8 details the autosampler component. Samples are transferred from the desired well in the microtiter plate into the columns of the Brio cartridge. If a 384-well plate is employed, the autosampler will carry out 3 sets of 8 injections into the columns, for a total of 24 columns. The solvent (mobile phase) does not circulate in the cartridge but is diverted into a backpressure regulator located in the waste line (Figure 6.2). This process of injection is known as stop-flow injection. After all samples are placed into the injection pits of the 24 columns in the cartridge (Figure 6.5), a clamp containing a seal...

The truly parallel approach employed in the design of the /./Pl.C system described in this chapter produces a clear reduction in analysis time when compared with traditional HPLC techniques. For example, a separation method of 5 min duration in a //Pl.C system would allow simultaneous evaluation of 24 samples within that time—an average analysis time of 12.5 sec/sample. Similarly, the dimensions of the columns housed in the cartridge require smaller amounts amount of solvent (mobile phases) for the analysis. 

Solvent strength is a designation of the ability of a solvent (mobile phase) to elute mixture components. The greater the solvent strength, the shorter the retention times. 

Eor the analysis of petroleum hydrocarbons, a moderately polar material stationary phase works well. The plate is placed in a sealed chamber with a solvent (mobile phase). The solvent travels up the plate, carrying compounds present in the sample. The distance a compound travels is a function of the affinity of the compound to the stationary phase relative to the mobile phase. Compounds with chemical structure and polarity similar to those of the solvent travel well in the mobile phase. For example, the saturated hydrocarbons seen in diesel fuel travel readily up a plate in a hexane mobile phase. Polar compounds such as ketones or alcohols travel a smaller distance in hexane than do saturated hydrocarbons. 

Developing an isolation approach is an activity that is frequently overlooked or addressed as an afterthought. However, solubility and stability data may dictate the development of a chromatographic method that requires the elaboration of the isolation, that is, it is more complicated than a simple evaporation of the mobile phase. The development of the chromatographic process should be linked to and interactively codeveloped with the isolation. Ideally, the isolated impurity sample should not contain other compounds or artifacts, such as solvents, mobile-phase additives or particulate matter from the preparative chromatography, as they may interfere with the structure elucidation effort or adversely affect the stability of the impurity during the isolation process. Therefore, it is preferable to avoid or minimize the use of mobile-phase additives. However, should this prove to be impossible, the additive used should be easy to remove. The judicious choice of mobile phase in the HPLC process increases the ability to recover the compound of interest without or with minimum degradation. The most common... 

The solvent mobility in atactic polystyrene-toluene solutions has been studied as a function of temperature using NMR. The local reorientation of the solvent was studied using deuterium NMR relaxation times on the deuterated solvent. Longer range motions were also probed using the pulsed-gradient spin-echo NMR method for the measurement of diffusion coefficients on the protonated solvent. The measurements were taken above and below the gel transition temperatures reported by Tan et al. (Macromolecules, 1983. 16, 28). It was found that both the relaxation time measurements and the diffusion coefficients of the solvent varied smoothly through the reported transition temperature. Consequently, it appears that in this system, the solvent dynamics are unaffected by gel formation. This result is similar to that found in other chemically crossed-linked systems. 

The gel continuously proceeds towards the stable equilibrium, but does not reach it within reasonable periods of observation. Second, the solvent mobility is modified by the gel formation. Water is included into the structure and stabilizes the helices. These two features seem to be common to a great number of physical polymer gels. 

To compare the separation performance of two columns containing the same media, the flow rate of the solvent (mobile phase)... 

Detector UV detection at 230 nm Sample solvent mobile phase... 

Solvent (mobile phase) from a solvent reservoir is pulled up the solvent inlet line into the pump head through a one-way check valve. Pressurized in... 

Solvates (hydrates) Same as for true polymorphs 0.5-2 Unique solvent resonances, shifted drug resonances, solvent mobility may be assessed 0.5-5 Solvent bands and shifted absorption bands due to H-bonding interactions 5-10... 

Figure 14.3 Chromatograms of excipients in film-former class under different mobile phase pH. In both plots, the curves from the bottom are blank, HPMC, acacia, sucrose NF, HPC, povidone and Eudragit EPO, respectively. The sample solvent, mobile phase and column used are (a) 20% ACN-80% pH 2, 25 mM phosphate buffer, a gradient from 30% ACN-70% pH 2, 25 mM phosphate buffer to 80% ACN-20% pH 2, 25 mM phosphate buffer and a Zorbax SB-C8, 4.6 x 150 mm, 3.5 p.m column at 35°C, respectively and (b) 20% ACN-80% pH 7, 25 mM phosphate buffer, a gradient from 30% ACN-70% pH 7, 25 mM phosphate buffer to 80% ACN-20% pH 7, 25 mM phosphate buffer and a Zorbax XDB-Cg, 4.6 x 150 mm, 3.5 p,m column at 35°C, respectively. In both cases, samples were injected at 1800 p,L, the flow rate of mobile phase was 1 mL/min and the detection was at 210 nm. An on-bench examination of the mixture of either 80% ACN-20% pH 2, 25 mM phosphate buffer or 80% ACN-20% pH 7, 25 mM phosphate buffer revealed no precipitation, so they were suitable as the mobile phase.

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