Mobile phase influence

Does solubility in the mobile phase influence net retention Polyethylene glycols are more soluble in cold solvents than warm. What is the noted effect if the temperature of the liquid chromatography separation of poly ethers is raised ... 

The dielectric constant of the mobile phase influences the pK value of the dissociable substructure of the analyte, it decreases with decreasing dielectric constant. This relationship can be approximately described by... 

For these three materials, covalent bonding technologies cannot be used. With silanes, mixed anhydrides are formed lacking in hydrolytic stability. Coating with organic polymers [32] is the way to go. A bonded phase based on zirconia has been studied widely [43]. Method development strategies established with silica-based RP cannot be transferred to an RP bonded on zirconia. Selectivity is dependent, e.g., on the type of buffer used. Anions in the mobile phase influence retention. The kinetics of analyte interaction with the different active sites may lead to reduced efficiencies. 

Similar to GC instruments, HPLC instruments consist of an injection port, a separation column, a detector, and an instrument control/data acquisition computer. The use of liquid as a mobile phase influenced the design and construction materials of HPLC instrumentation elements. A sample extract or an aqueous sample is introduced into the separation column through an injection loop that can be programmed to receive various volumes of liquid (5 pi to 5 ml). 

As shown in Figure 13-7, the pH of the mobile phase influences the retention of the various compounds in the sample. What does this imply about the qualitative nature of retention time in HPLC Is HPLC a quantitative or qualitative tool ... 

Castillo, J. Benavente-Garcia, O. Del Rio, J.A. Study and optimization of Citrus flavanone and flavones elucidation hy reverse phase HPLC with several mobile phases Influence of the stmctural characteristics. J. Liq. Chromatogr. 1994, 17 (7), 1497-1523. 

When a compound contains one or more dissociable polar substituents, the pH and the ionic strength of the mobile phase influence the apparent lipophilicity of the compound. Usually, the mobile phase is buffered at a pH which ensures the neutral form of the studied compound. 

The viscosity of the mobile phase influences the backpressure and efficiency of the separation. The higher the back-pressure, the lower the flow rate that can be used and, consequently, the longer the run time. Lowering the viscosity increases mass transfer and, hence, the efficiency of the separation is improved (the peaks are narrower). Although the maximum flow rate does not provide the maximum separation, it does maximize the production rate. 

The most important step in developing a chromatographic system is the choice of mobile phase. Although the mobile phase influences the separation process in many ways, the main decision parameters for the choice of the mobile phase are the maximum solubilities cs of the target components and the selectivity of the separation. Solubility is essential for the productivity of the chromatographic separation process, because it is a precondition for exploiting the whole range of column loadability. 

Figure 13.13 Chromatogram of a pure component with a binary mobile phase. Influence of the retention of the additive additive more strongly retained than the component > i)-(a) Same experimental conditions as for Figure 13.12a, except flg = 40 bs = 20. (b) Same conditions as for Figure 13.12a, except fls = 200 bs = 100. Reproduced with permission from S. Golshan-Shirazi and G. Guiochon, f. Chromatogr., 461 (1988) 1 (Figs. 3 and 4).

Further, Garcia et al. [16] found that changes in the concentration of surfactant and alcohol, in the mobile phase, influence llie relative errors obtained with eq. 8.26, which were lower for CTAB with respect to SDS, and for 1-propanol with respect to 1-butanol. This simple model failed in taking into account some interactions of the solutes, which are more important in very hydrophobic systems and when solute-micelle interactions are diminished. It should be considered that the amount of surfectant on the column desorbed by 1-butanol is greater than by 1-propanol. Also, 1-butanol can compete to a greater extent than 1-propanol with the micelle, in the interaction with the solutes. Eq. 8.28 (with a term) provided a better description of the retention for highly hydrophobic polycyclic aromatic hydrocarbons (PAHs) than eq. 8.26 (Fig. 8.7). For these compounds, the plot of 1/k vs. (p was nonlinear. Similar results were obtained for several steroids eluted with SDS-acetonitrile eluents [17]. 

It can be easily recognized from equation (9) that the velocity of the mobile phase Influences the column efficiency more strongly than other operational variables. Though the retention volume of a solute should be constant for a given column and seems to be Independent of the flow rate, the value of the retention volume changed with change in the flow rate and the peak width increased with an increase in the flow rate. Consequently, the values of N decreased with an Increase in the flow rate and were approximately Inversely proportional to the root of the flow rate [ref. 11]. 

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