Elution liquid chromatography

The elution volumes of polystyrene and benzene in the size-exclusion mode were 0.98 and 1.78 ml, respectively (Figure 1.4A). This means that separations by molecular size can be achieved between 0.98 and 1.78 ml in this system. In the normal phase mode the elution volumes of octylbenzene and benzene were 1.98 and 2.08 ml, respectively, in n-hexane solution (Figure 1.4B). This type of chromatography is called adsorption or non-aqueous reversed-phase liquid chromatography. These are adsorption liquid chromatography and non-aqueous reversed-phase liquid chromatography. The elution order of the alkylbenzenes in the reversed-phase mode using acetonitrile was reversed... 

In the laboratory conducted portion of the organic analysis, a seven step liquid elution chromatography separation on silica gel forms the central part of the scheme. It is an analytical step (in that behavior of a given class of compounds is predictable) as well as a separation step (since the fractions may be further analyzed much more readily than the original mixture). The behavior of selected classes of compounds with respect to the chromatographic conditions employed is shown in Figure 4. 

Applying liquid chromatography by eluting with a polar solvent to separate two of the principal glycosides. 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

Liquid-Liquid Chromatography. Liquid-liquid chromatographic (LLC) separations result from partitioning of solute (analyte) molecules between two immiscible liquid phases (10). The liquid mobile and liquid stationary phases ideally have little or no mutual solubility. The stationary liquid phase is dispersed on a column of finely divided support. The use of a nonpolar mobile phase and a polar stationary phase is referred to as normal phase LLC. Under these conditions, less polar solutes are preferentially eluted from the column. Reverse phase chromatography employs a nonpolar stationary phase and a polar mobile phase. Generally, polar compounds elute more rapidly with this technique. Reverse phase chromatography, useful for the separation of less polar solutes, has found increased application in occupational health chemistry. It is optimally suited to the separation of low-to-medium molecular weight compounds of intermediate polarity. 

For metabolite isolation, 1.5 liters of pooled urine were applied to a XAD-2 resin column first. The ethyl acetate extract obtained containing 85 % of the radioactivity was applied upon evaporation to semipreparative HPLC on a Zorbax RX C18 column (9.4 x 250 mm, 5 pm) using gradient elution. Fractions obtained were further separated by isocratic elution on the semipreparative column. The metabolite fractions obtained were finally purified by preparative thin-layer chromatography. Liquid chromatography/mass spectrometry (LC/MS) and LC/MS/MS analysis was applied to the isolated metabolite fractions for structure elucidation. 

For the low concentrations used in liquid chromatography, the elution peak is Gaussian in shape and its retention factor is independent of the sample size. When isotherms are nonlinear (convex or concave, as illustrated in Fig. 1), an asymmetric elution peak is obtained and the retention factor measured at the peak apex is dependant on the sample size. 

Figure 3 shows a high-pressure liquid chromatography (HPLC) elution pattern of isomeric P-carotene (Koyama et al., 1988b Hu etal, 1997). Ibe mono-ds isomers elute in the order from the central-cis to the peripheral-cis isomers, the retention time being in the order, l5-cis < l3-cis< 11-ds <9-cis <... 

Cobalt oxide, as adsorbent additive, 177 Column chromatography, see Elution Column length, effect on N, 115-117 Column packing, see HETP values Column pressure, effect on TV, 115-117 Coluisns, for liquid chromatography, 347-348... 

Comprehensive multidimensional liquid chromatography is a relatively new development and has yet to develop a diverse application base. For the time being applications are dominated by the separation of proteins and synthetic polymers. For proteins the first dimension separations are usually based on ion exchange and the second dimension separations on reversed-phase liquid chromatography. Gradient elution was often used for both separation modes with a separation time less than 2 minutes for the second dimension separation and from 30 minutes to several hours for the first dimension separation. Current trends include the use of non-porous particles and perfusive stationary phases for the second dimension separation to reduce the total separation time and wider internal diameter columns in place of packed capillary columns to simplify interface construction and instrument operation and to allow the loading of larger sample sizes. 

Standards a stock solution (2.5 mM) of SN-38 glucuronide (kindly supplied by Yakult Honsha Co. Ltd.) is dissolved in 5 mL of methanol. A working solution (0.5-250 iiM) for calibration curves is prepared by the serial dilution of the 2.5 mM stock solution with high-performance liquid chromatography (HPLC) elution buffer. 

The activity coefficient is the most important and fundamental property in the thermodynamic study of liquid mixtures. It is a measure of the deviation of the behaviour of a component in a mixture from ideality and it has been interpreted by various theories of liquid mixtures. Gas-liquid elution chromatography offers a rapid method of determining this property at infinite dilution. Conder and Purnell have developed a method of determining activity coefiicients at finite concentrations and this has recently been used by other workers. " To do this, the elution technique must be supplemented by... 

In liquid elution chromatography, separation is based on adsorption on the solid or on partition to a stationary or bonded liquid phase. Distribution coefficients are modest so that solutes migrate through the column as shown in Figs. 14.1-2 and 14.1-3. Gradients can be used but usually are not since the column has to be reequilibrated afterward. Two somewhat different approaches have bMn taken ... 

An aqueous solution of NaCl, NaN03, and Na2S04 was passed through a Cig-silica reversed-phase liquid chromatography column eluted with water. None of the cations or anions is retained by the Cjg stationary phase, so all three salts were eluted in a single, sharp band with a retention time of 0.9 min. Then the column was equilibrated with aqueous 10 mM pentylammonium formate, whose hydrophobic tail is soluble in the C18 stationary phase. 

Alkyl substituents (specifically the octadecyl ODS form) are the most common bonded groups these convert the surface polar hydroxyl groups to a markedly hydrophobic surface upon which chromatography occurs. Elution is carried out with polar solvents such as water and methanol there is a polarity reversal of the stationary and moving phases compared with conventional liquid chromatography on silica, hence the term reverse-phase HPLC. 

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