Polymer stationary phase

Polymer Stationary phase Supplier Mobile phase Detection... 

Figure 3.2 Chiral polymer stationary phases for HPLC.

Non-silica-based RP-HPLC stationary phases have also been developed and their separation capacity has been compared with those of silica-based ones. The porous structure of crosslinked polymer gels may be responsible for the markedly different selectivity and retention characteristics. Up till now, the mode of separation on polymer stationary phases is not entirely understood at the molecular level. It has been established that the size-exclusion effect may influence the retention of analyses on polymer gels. 

These separations can be carried out using a silica-based bonded phase however, the important advantage of organic polymer stationary phase materials is their chemical stability. The columns can be washed by using an alkaline solution after a certain number of injections. According to the chromatograms, the proteins in serum are completely eluted and nothing remains inside the column. However, the pressure drop in this type of analysis... 

Three types of stationary phases based on the free-radical reaction of monocationic and dicationic vinyl-substituted imidazolium cations were studied [42]. Two examples of such monomers are given by ILs 9 and 10 in Table 4.1. The formation of a linear IL polymer stationary phase was performed by the free radical polymerizafion of monocationic monomers. 

The porous polymer stationary phases which for many years have been available in packed gas chromatography columns has only recently become available as a coated capillary [24]. These cross-linked porous polymer columns are produced by copolymerizing styrene and divinylbenzene. The pore size and surface are varied by altering the amount of divinylbenzene added to the polymer. These PLOT capillary columns exhibit the same separative characteristics as Poropak Q packed columns. 

Table 2.6 shows a series of silicone polymer stationary phases from the OV series. These are dimethylsiloxane polymers, with a varying percentage of the methyl groups replaced by phenyl groups. It turns out that the Rohrschneider constants closely follow this increase in phenyl group percentage. The constants therefore appear to be a reliable indication of the polarity of the stationary phase. 

Thus, a reference polymer imprinted with benzylamine, as a stationary phase, was prepared and used to validate the model. pH-curves of the product of solute and MIP ionization (a a ) and of the retention profiles of benzylamine and (/ ,S)-(1) on the benzylamine-selective cationic-imprinted polymer stationary phase showed excellent agreement (see Fig. 9.29b). 

While the determination of the glass transition temperature of polymer stationary phases by inverse gas chromatt t lqf seems well-establiriied, several authors 11,15, 2 7) reported the failure of the technique to detect known transitions. In-... 

A prime objective of early studies of polymer stationary phases was to assess the reliability of GC-detived activity coefficients and interaction parameters. Conventional static methods of measurement are difficult and time-consuming, and data on relatively few systems are available for the purpose of comparison. The facility with which such data can be obtained by gas duromatc r hy diould remedy this situation. In order to achieve a meaningful comparison, results from static methods must be extrapolated to infinite dilution, owing to the concentration dependence of the interaction parameter. 

The experimental work reported up to this point has dealt exclusively with solutes at infinite dilution in the polymer stationary phase. Recent theoretical advances (S8, 70) have made it possible to extend the ran of gas chromatc t hy to flnite concentration of the solute in the stationary phase. In the caM of polymers arch studies should provide a direct insight into the concentration dependence of the interaction parameter and allow for comparison with static results without recourse to extrapolations to infinite dilution. 

Following the theoretical treatment of Conder and Purnell 38, 7G) of gas chromatography at finite concentration, Brockmeier eraf 71, 72) applied the method to polymer stationary phases. For the technique of elution on a plateau of finite concentration, the we t fraction activity coefficient is given by the relation (.71),... 

The determination of the crystallinity of polymer stationary phases is based on the differential solubility of the K>lute in crystalline and amorjdious domains. In effect the solute senses only the amorphous regions, leading to an increa in retention volume with decreasing crystallinity. 

DeVries, Smit and Smith 100) reported heats of adsorption on cellulose triacetate (44.8% acetyl) and diacetate (25% acetyl) using alcdiols and aromatics as solutes. They observed a systematic difference in heats of adsorption for each solute between both polymer stationary phases, indicating a difference in partial molar heats. They discussed their results in terms of nonspecific and hydrogen bonding interactions between the polymers and the solutes. 

From the ape of the eluting solute peak, information can also be gained on the kinetic processes operative in a GC column. As the solute propesses from iidet to outlet, the band of solute molecules broadens due to diffusional spreading in both gas and liquid phases. Under suitable experimental conditions the diffusion coefficient of the solute in the polymer stationary phase can be determined from the width of a symmetrical eluted peak. 

Niederstrass (108) used gas chromatography to characterize polymer stationary phases of differing styrene/butadiene contents. These induded mechanical mbctures of polystyrene and polybutadiene, statistical and graft copolymers as well as block... 

The "family-plot retention data of 5 solutes with a series of poly(methylphenylsiloxane) stationary phases have been examined in terms of the saturation vapor pressure Pa of the solute, the methyl/phenyl ratio of the solvent, and the temperature. Plots of In Vg against In p for a given solute over a range of temperature were found to De linear, as were the "isothermaV, that is, the retention/vapor -pressure plots for an homologous series of solutes at a constant temperature. The family-plot slopes exhibited by the n-alkane probe-solutes were also found to be very sensitive to the aromatic content of the polymers. Thus, it appears that the "family" technique of GC data reduction can be a useful tool for characterizing the physicochemical properties of (polymer) stationary phases. 

A conceptual difficulty arises in characterizing polymer stationary phases with gas-liquid chromatographic probe-solute specific retention volumes (1), namely, since it is a matter of experience that V remains finite, the mole fraction-based solute activity coefficient x must asymptotically approach zero as the molecular weight of the polymer stationary phase Mg becomes large . ... 

However, the derivation of Equation 16 failed to take into account the free-volume ("structural") contribution to xy"(35), nor is the effect negligible with some polymer phases (36). In addition, there remains considerable doubt even as to what constitutes a "family" set of data e.g., with polymers that are liquid-crystalline. The characterization of polymer stationary phases via family-plot regressions of "inverse" gas-chromatographic retentions therefore invites further and comprehensive study. 

Critical temperature The temperature above which a substance can no longer exist in the liquid state, regardless of pressure. Cross-linked stationary phase A polymer stationary phase in a chromatographic column in which covalent bonds link different strands of the polymer, thus creating a more stable phase. Crystalline membrane electrode Electrode in which the sensing element is a crystalline solid that responds selectively to the activity of an ionic analyte. 

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