Specific retention volume chromatography

The separation of mixtures involving N-methyl-JLtetrahydropyridines into their pure components by means of gas-liquid chromatography was discussed in a report by Holik et al. (87). They found that, using tris(/3-cyanoethoxymethyl)-y-picoline as the stationary phase, the primary factors involved in the specific retention volumes of these enamines is the electronic effect of a methyl substituent and the nitrogen atom on the carbon-carbon double bond. It was observed that 1,3-dimethyl-Zl -tetrahydropyridine (141) has a smaller specific retention volume and, hence, is eluted before... 

VR has been used in gas-solid chromatography to represent corrected retention volume (49), whereas corrected retention volume in gas-liquid chromatography is given the symbol VR- Specific retention volume in gas-solid chromatography is V, but in... 

Benzene was passed at various temperatures through a gas chromatography column packed with silica gel and the following specific retention volumes (extrapolated to zero sample size) were measured ... 

The gas chromatographic method is based on the relation between the differential enthalpy of adsorption at zero coverage and the temperature dependence of the Henry s law constant, kn, as expressed in the form of Equation (4.3). In the low-pressure region, where Henry s law applies, the specific retention volume, Vj, is a linear function of kH (Purnell, 1962 Littlewood, 1970). This relationship makes it possible to make use of elution chromatography since... 

Lichtenthaler, R. N. Newman, R. D. Prausnitz, J. M., "Specific Retention Volumes from Gas-Liquid Chromatography for Poly(dimethylsiloxane)- Hydrocarbon Systems," Macromolecules, 6, 650 (1973). 

Tyagi, O. S. Deshpande, D. D., "Inverse Gas Chromatography of Poly(n-butyl methacrylate) Effect of Flow Rate on Specific Retention Volume and Detection of Glass Transition Temperature," 34, 2377 (1987). 

Unfortunately, in many instances the materials employed as sensor coatings are nonvolatile solids (polymers) for which 6 values cannot be calculated directly. Solubility parameters for these materials can be estimated, however, by immersion testing [172b], inverse gas chromatography [173,174] or ftom coated-SAW sensor responses [166]. In inverse chromatography, the polymeric coating material is used as a stationary phase on a GC column, and the specific retention volumes (V ) for several solutes are determined. Since the Vg is directly related to, Kc, the solubility parameter for the polymer coating can be derived from relationships similar to Equation 5.32. A similar approach is used to derive S, from SAW sensor response data [166]. 

Inverse gas chromatography, IGC, has been used to study water sorption of two poly (vinylidene chloride-vinyl chloride) and poly (vinylidene chloride-acrylonitrile) copolymers, at temperatures between 20 and 50°C and low water uptakes. It was found that the specific retention volume of water increases with decreasing amount of water injected, increases dramatically with decreasing temperature and strongly depends on the type of copolymer. Thermodynamic parameters of sorption namely free energy, entropy, enthalpy of sorption and activity coefficient were calculated. 

The usefulness of inverse gas chromatography for determining polymer-small molecule interactions is well established (1,2). This method provides a fast and convenient way of obtaining thermodynamic data for concentrated polymer systems. However, this technique can also be used to measure polymer-polymer interaction parameters via a ternary solution approach Q). Measurements of specific retention volumes of two binary (volatile probe-polymer) and one ternary (volatile probe-polymer blend) system are sufficient to calculate xp3 > the Flory-Huggins interaction parameter, which is a measure of the thermodynamic... 

An alternative method of data reduction was reported early in the history of gas chromatography by Hoare and Purnell (12-15 see refs. 16,17 for recent applications), who considered the dependence oTffie specific retention volume on the solute saturation vapor pressure pA. Thus, taking the view [now recognized to be naive (18) see later], that the observed mole fraction-based solute activity coefficient" can be decomposed into "athermal" and "thermal" components (19-22) v v-... 

In gas chromatography it is often advantageous to work with the so-called specific retention volume [19] which is defined by the relation... 

Not only variations in the pressure at constant temperature influence column-to-column retention data the role of the column hold-up volume as well as the mass of stationary phase present in the column is also important. The net retention volume caleulated from the adjusted retention volume corrects for the column hold-up volume (see Table 1.2). The specific retention volume corrects for the different amount of stationary phase present in individual colunms by referencing the net retention volume to unit mass of stationary phase. Further correction to a standard temperature of 0°C is discouraged [16-19]. Such calculations to a standard temperature significantly distort the actual relationship between the retention volumes measured at different temperatures. Specific retention volumes exhibit less variability between laboratories than other absolute measures of retention. They are not sufficiently accurate for solute identification purposes, however, owing to the accumulation of multiple experimental errors in their determination. Relative retention measurements, such as the retention index scale (section 2.4.4) are generally used for this purpose. The specific retention volume is commonly used in the determination of physicochemical properties by gas chromatography (see section 1.4.2). 

Equation 12 takes account as well of solute/stationary-phase partitioning in the instance of gas-solid chromatography since, in the absence of adsorbent-adsorbent interactions, (adsorbate) solute specific retention volumes are described exactly by the weight-average of the retentions with the pure adsorbents (37). This holds also in the instance of adsorbate/adsor-bent charge-transfer complexation, i.e., equations 14 and 15 (38). 

The sorption properties of the above carbonaceous materials were examined by means of gas chromatography [420], which allows quantitative characterization of sorbent-sorbate interactions at a small coverage of sorbent surface. Table 17.3 presents the specific retention volumes of various organic compounds measured for different carbons. 

Heats of Transfer between Solvents. Kurkchi and logan (147) have used gas-liquid chromatography to determine specific retention volumes of acetylene (23), propyne (24), and 1-butyne (25) in eight solvents (isooctane, 9,18,25,26,28,41,52) at a number of temperatures, and thence have derived heats of solution, AHy, and of transfer between solvents, AHij. The later quantities (transfer from isooctane to HBA solvents) are well correlated by /8 and x ... 

High pressure liquid chromatography affords accuracy and specificity. Retention volumes help in identification as they are reliable in a conditioned HPLC-system. 

Preliminary experiments for MMA-SMA graftcopolymers were carried out to examine the surface activity of the graftcopolymers.5) Inverse gas chromatography, using a pol nner studied as the stationary phase, is a convenient and useful method for characterizing the surface and bulk properties of surface active copol nners. Polymers were coated on Chromosorb G (AW-DMCS treated, 60-80 mesh) from the chloroform solutions by evaporation. The polymer-coated supports were packed in a column and conditioned in the gas chromatograph oven at 160 for 5 hours. The specific retention volume for n-dodecane (where... 

The retention mecheinism in gas-solid chromatography with vapor mobile phase is complex. Interfacial adsorption processes, influenced by coop-erativity and steric effects are the predominant mechanisms in addition, the bulk solubility may operate at high pressures (multilayer adsorption) of modifiers. Parcher, Lin eind Johnson [75] suggested the specific retention volume equation, which provides the first quantitative description for retention of one solute as a function of the surfoce coverage by a second component (modifier) ... 

When columns filled with NaY and also with CdY zeolite were used with carbon dioxide as carrier gas, a considerable decrease in specific retention volumes of hydrocarbon gases was obtained, especially at low temperatures typical of carbon dioxide adsorption on zeolites, screening of cations and partial deactivation of the adsorbents. Use of carbon dioxide as carrier gas improves the separating ability of zeolites without complete suppression of the cation effects on the separation and widens the range of zeolite applications in gas chromatography [109]. 

Gas-liquid Chromatography (g.l.c.).—Letcher has reviewed the use of g.l.c. to obtain activity coefficients in non-poiymer systems. The method is claimed - to be an accurate means of obtaining thermodynamic quantities in binary solutions when the two components differ considerably in volatility. Clearly this applies to many polymer-solvent systems and then the pol3rmer is conveniently made to form the stationary (liquid) phase in standard equipment. The solvent of interest is introduced into the mobile (gas) phase and its specific retention volume measured, from which heats of mixing are calculated > in the limit of zero concentration of solvent (a limit of interest in connection with the removal of volatiles from polymeric materials - ). 

AH can be measured by inverse gas chromatography, as follows. The solid analyte is installed in gas chromatography as a solid stationary phase, a solvent with known values of C and E is used as a probe, and specific retention volume v° is measured at different temperatures. Then Formula 2.3 is used to calculate the enthalpy change of the interaction with the stationary phase. 

Table 86. Gas chromatography of silyl ethers and silyl thioethers Specific retention volumes on apiezon L...

A complete theory predicting retention times or volumes as function of molecular size has not yet been formulated for gel permeation chromatography. A specific column or set of columns is calibrated empirically to give such a relationship, by means of which a plot of amount of solute versus retention volume (the chromatogram figure below) can be changed into a molecular-size-distribution curve. Generally commercially available narrow... 

The specific pore volume is important in size-exclusion chromatography (SEC) [10] because the separation takes place there. In retentive chromatography, it is necessary to provide the surface area... 

Sund et al. 101) and also Wallace et al. 20) reported retention characteristics of poly(vinyl chloride) powders of differing specific surface areas. It was shown that, once a calibration curve was established, gas chromatography could provide a rapid determination of surface areas of poly(vinyl chloride) powders. At temperatures below Tg the measured retention volume should be proportional to the surface partition coefficient and to the surface area of the stationary phase as expressed in Eq. (28). From the known airface areas of several samples the partition coefficient can be obtained, in turn allowing for the determination of the surface area of any sample from the measured retention volume. A similar correlation between BET surface areas and retention volumes was reported by Salovey et al. 102) for poly(vinyl chloride) powders. 

---