At-column-dilution

Blom KF. Two-pump at-column-dilution configuration for preparative liquid chromatography-mass spectrometry. J. Comb. Chem. 2002 4 295-301. 

Fig. 4.13 Scheme of conventional column loading (left) and at-column-dilution (right). 

At-column dilution allows for processing of low-soluble samples often in large volumes of strong or aggressive solvents and reprocessing of the chromatographic fractions enriched with the target material. 

Activity coefficients at infinite dilution, of organic solutes in ILs have been reported in the literature during the last years very often [1,2,12,45,64, 65,106,123,144,174-189]. In most cases, a special technique based on the gas chromatographic determination of the solute retention time in a packed column filled with the IL as a stationary phase has been used [45,123,174-176,179,181-187]. An alternative method is the "dilutor technique" [64,65,106, 178,180]. A lot of y 3 (where 1 refers to the solute, i.e., the organic solvent, and 3 to the solvent, i.e., the IL) provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor of the components to be separated at infinite dilution to determine the applicability of a compound (a new IL) as a selective solvent. 

Several manufacturers offer GC-FT IR instruments with which a vapor-phase spectrum can be obtained on nanogram amounts of a compound eluting from a capillary GC column. Vapor-phase spectra resemble those obtained at high dilution in a nonpolar solvent Concentration-dependent peaks are shifted to higher frequency compared with those obtained from concentrated solutions, thin films, or the solid state (see Aldrich, 1985). 

In 1995 Leigh et al. reported a catenane synthesis that is convincing not only because of its simplicity but also because it is accessible to a wide variety of reactants [24]. When isophthaloyl dichloride (3) was reacted with l,4-bis(aminometh-yl)benzene at high dilution [2]catenane 28 was isolated in 20% yield without further purification by column chromatography (Figure 13). 

Bj2 - vi )/RT, v = the partial molar volume of the sample at infinite dilution in the stationary (liquid) phase, (1) refers to the sample, (2) to the carrier gas, (3) to the stationary liquid, and is a function of the column inlet and outlet pressures, and pQ. 

In the inverse GC at infinite dilution or near zero surface coverage, the surface characterization of the solid are realized by injecting very small quantities of probes of known properties into a column packed with the solid. The retention time can be the fundamental parameter characterizing the equilibrium distribution of the probe concentration between the probes where all probe molecules behave independently. Therefore, the retention time is a function only of the adsorbate-adsorbent interaction [111]. 

Since the intermolecular adsorption of Gibbs free energy, —AGa, in Eq. (48), is independent of the specific surface area and weight of the solid in the column, except for the net retention volume, Fn, in the inverse GC at infinite dilution. Therefore — AGa can be rewritten... 

The product [t]]M is a direct function of the hydrodynamic volume of the solute at infinite dilution. Two different polymers which appear at the same elution volume in a given solvent and particular GPC column set therefore have the same hydrodynamic volumes and the same [t]]M characteristics. 

The basis for determining the required number of plates or column efficiency at infinite dilution is to solve the simplified Knox equation in terms of the optimum d /L (Eq. (7.19)). 

Thus, the fugacity of species i (in both the hquid and vapor phases) is equal to the partial pressure of species i in the vapor phase. Its value increases from zero at infinite dilution (jc, = y, -> 0) to Pj for pnre species i. This is illnstrated by the data of Table 12.1 for the methyl ethyl ketone(l)/toluene(2) system at 323.15 K (50°C). The first tlnee columns list a set of experimental P-x -y data and colunms 4 and 5 show ... 

Combination of the AjH (Na0H aq, , 298.15 K) values with the enthalpy of solution of NaOH(cr) at infinite dilution given above, results in the A H (NaOH, cr, 298.15 K) values given in the last column. The value determined from the work of Gunn and Green (4) is adopted. 

A quantitative bioassay for erythromycin 2 -ethylsuccinate (EM-ES, M, 861 Da), a prodrug of the macrolide antibiotic erythromycin, using Cf-FAB LC-MS was described by Kokkonen et al. [53-54]. Reversed-phase LC of extracted plasma samples was performed at a flow-rate of 1 ml/min. In order to meet the flow-rate requirements of the Cf-FAB interface, i.e., 15 pl/min, without splitting, the phase-system switching approach [53] was used. After post-column dilution of the column effluent with water, the eluent fraction of interest was enriched on a short precolumn, from which the compound of interest was desoibed and transferred to the Cf-FAB interface probe. A [ Hj]-analogue was used as internal standard. Good linearity was observed in the range of 0.1 to 10 pg/ml EM-ES in plasma. The within-ran precision was ca. 6%. The accuracy and inter-day precision, determined at 1.05 pg/ml in plasma, were 0.93 0.11 pg/ml and 12%, respectively (n=6). The determination limit was 0.1 pg/ml [54]. 

X Ammonium sulphate precipitation is a common sample clarification and concentration step at laboratory scale and in this situation HIC (which requires high salt to enhance binding to the media) is ideal as the capture step. The salt concentration and the total sample volume will be significantly reduced after elution from the HIC column. Dilution of the fractionated sample or rapid buffer exchange using a Sephadex G-25 desalting column will prepare it for the next IEX or AC step. 

Diffusivity data are available only for a limited number of polymer-solvent systems. This paper describes research that has led to the development of the use of capillary column inverse gas chromatography (IGC) for the measurement of diffusion coefficients of solute molecules in polymers at infinite dilution. The work has resulted in a precise, rapid technique for the diffusion measurements that circumvents the many problems attendant to classical sorption methods and packed column IGC methods. Initial results of the program appeared in two recent publications (1,2)- Some of the material introduced in those papers is discussed here to present background for... 

Using a similar experimental set-up as for the determination of Abraham s solvation parameters, the activity coefficient of solutes at infinite dilution y" cm be determined from their retention times using gas-liquid chromatography [12, 67-72], Alternatively, the diluter technique is applied [67, 73] for which an inert gas transports the solute from the headspace (which is in equilibrium with the ionic liquid matrix) to a GC-column. The continuous decrease of the concentration in the headspace is measured as a function of time, generating an exponential function from which y°° is calculated. 

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