Mobile phase model

Coals as macromolecular/molecular two-phase systems - the host/guest or rlgld and mobile phase model (3-5) ... 

In their original theoretical model of chromatography, Martin and Synge treated the chromatographic column as though it consists of discrete sections at which partitioning of the solute between the stationary and mobile phases occurs. They called each section a theoretical plate and defined column efficiency in terms of the number of theoretical plates, N, or the height of a theoretical plate, H where... 

In this experiment a theoretical model is used to optimize the HPLC separation of substituted benzoic acids by adjusting the pH of the mobile phase. An empirical model is then used... 

Two mechanisms for chiral separations using chiral mobile-phase additives, analogous to models developed for ion-pair chromatography, have been... 

An alternative model has been proposed in which the chiral mobile-phase additive is thought to modify the conventional, achiral stationary phase in situ thus, dynamically generating a chiral stationary phase. In this case, the enantioseparation is governed by the differences in the association between the enantiomers and the chiral selector in the stationary phase. 

Usually goodness of fit is provided by adding new parameters in the model, but it decreases the prediction capability of the retention model and influences on the optimization results of mobile phase composition. 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

The model was tested by the micellar liquid chromatography separ ation of the five rarbornicin derivatives and four ethers of hydroxybenzoic acid. Micellar mobile phases were made with the sodium dodecylsulfate and 1-pentanol or isopentanol as modifier. In all cases the negative signs of the coefficients x and y indicate that at transition of the sorbat from the mobile on the stationar y phase the number of surfactant monomers as well as the number of modifier molecules increases in its microenvironment. 

With regard to the line 1, the development eould be noted for the following methods those, where peroxide derivatives of earboxylie aeids are used methods of multiple-wavelength speetrophotometrie analysis methods of quantitative aeeounting of a priori information methods of liquid ehromatography (a Unified adsorption eenter model and a Mobile phase effeetive eoneentration eoneeption an applieation of mieellar ehromatography standardization of TLC-plates). 

By modeling the substance behavior at the interface of two liquid phases, in particular, stationary and mobile phases in liquid chromatography, 1-octanol - water partition coefficients or partition coefficients in... 

The coupling of supercritical fluid extraction (SEE) with gas chromatography (SEE-GC) provides an excellent example of the application of multidimensional chromatography principles to a sample preparation method. In SEE, the analytical matrix is packed into an extraction vessel and a supercritical fluid, usually carbon dioxide, is passed through it. The analyte matrix may be viewed as the stationary phase, while the supercritical fluid can be viewed as the mobile phase. In order to obtain an effective extraction, the solubility of the analyte in the supercritical fluid mobile phase must be considered, along with its affinity to the matrix stationary phase. The effluent from the extraction is then collected and transferred to a gas chromatograph. In his comprehensive text, Taylor provides an excellent description of the principles and applications of SEE (44), while Pawliszyn presents a description of the supercritical fluid as the mobile phase in his development of a kinetic model for the extraction process (45). 

The theory of the separation of geometric isomers on stationary phases that have a number of sterogenic centers has not been developed to the point where a particular stationary phase together with an appropriate mobile phase can be deduced for the separation of a specific pair of isomers. A number of theories have been put forward to explain the resolution of geometric isomers (some of which have been quite "imaginative" and "colorful") yet a reliable theory to help in phase selection for a hitherto unresolved chiral pair is still lacking. Unfortunately, the analyst is left with only two alternatives. The first is to search the literature for a model separation similar to the problem in hand and start with that phase system or, alternatively, resort to the technique of the early days of LC, namely, find the best phase system by a trial-and-error routine. 

The mobile phase consisted degassed distilled water containing 1.0 grams/liter of Aeorosol(B)-OT and varying amounts of sodium nitrate, NaNOj. The detector was a DuPont Model 840 UV photometer with a fixed wavelength of 254 nm. 

The apparatus employed for this study was a Waters Associates Model ALC/GPC 300 with a differential refractometer as mass detector operated at room temperature. A 2 ml sample loop with polymer concentrations of 0.01-0.1 wt.% cUid a 5 ml siphon were employed with mobile phase flowrates in the reuige 1-8 ml/min. 

From the general framework of the Snyder and Soczewinski model of the linear adsorption TLC, two very simple relationships were derived, which proved extremely useful for rapid prediction of solute retention in the thin-layer chromatographic systems employing binary mobile phases. One of them (known as the Soczewinski equation) proved successful in the case of the adsorption and the normal phase TLC modes. Another (known as the Snyder equation) proved similarly successful in the case of the reversed-phase TLC mode. 

The elaboration of the most efficient chromatographic systems for the optimization of velocity and resolution of the chromatographic process is necessary for solving different analytical problems. The most important factor in the TLC optimization is the mobile phase composition. Taking into consideration the similarity in the retention mechanism between TLC and PLC, the optimized TLC mobile phase can be transferred to the preparative chromatographic system. There are different accepted models and theories for the separation and optimization of chromatographic systems [19,20,61]. 

Snyder and Soczewinski created and published, at the same time, another model called the S-S model describing the adsorption chromatographic process [19,61]. This model takes into account the role of the mobile phase in the chromatographic separation of the mixture. It assumes that in the chromatographic system the whole surface of the adsorbent is covered by a monolayer of adsorbed molecules of the mobile phase and of the solute and that the molecules of the mobile phase components occupy sites of identical size. It is supposed that under chromatographic process conditions the solute concentrations are very low, and the adsorption layer consists mainly of molecules of the mobile phase solvents. According to the S-S model, intermolecular interactions are reduced in the mobile phase but only for the... 

The PRISMA model is a system for the optimization of two- to five-eomponent mobile phases, developed by Nyiredy et al. to simplify the optimization proeess in different planar and column chromatographic systems [66]. This model for the seleetion of solvents and optimization of the mobile phase was developed first for TEC and high-performanee liquid ehromatography (HPLC) [38,67]. 

FIGURE 4.11 The PRISMA model. (Adapted from Siouffi, A.-M. and Abbou, M., Optimization of the mobile phase, in Planar Chromatography, A Retrospective View for the Third Millennium, Nyiredy, Sz., Ed., Springer Scientific, Budapest, 2001, chap. 3. With permission.)... 

Determination of the optimum composition of the mobile phase using the PRISMA model... 

Morita et al. [69] optimized the mobile phase composition using the PRISMA model for rapid and economic determination of synthetic red pigments in cosmetics and medicines. The PRISMA model has been effective in combination with a super modihed simplex method for fadhtating optimization of the mobile phase in high performance thin layer chromatography (HPTLC). 

Pelander et al. [71] studied the retardation behavior of cyanobacterial hepato-toxins in the irregular part of the PRISMA model for TLC at 16 selectivity points. The mobile phase combination and the area of the triangular plane were selected in the preassay. The retardation of all the toxins followed the relation for ftRp. The cyanobacterial hepatotoxins behaved predictably in the selected systems in the irregular part of the PRISMA model. 

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