Stationary phase packed columns

Although the exact mechanism is not very clear, the following factors may contribute to the modifier effect on chromatographic retention. Polar modifiers may cover the active sites of the stationary phase (deactivation) so that solute retention is reduced. This can be explained by the differences in retention change between packed and open-tubular columns when small amounts of modifiers were used. Open-tubular columns normally do not show the drastic changes in retention or efficiency upon the addition of small amounts (<2%) of modifier as most packed columns do. These less drastic differences were caused by the differences in the degree of deactivation of the packed column stationary phase as compared with the open-tubular-column stationary phase. An open-tubular column has fewer active sites present and, thus, fewer active sites are present for the modifier to deactivate. 

The master retention equation of the solvation parameter model relating the above processes to experimentally quantifiable contributions from all possible intermolecular interactions was presented in section 1.4.3. The system constants in the model (see Eq. 1.7 or 1.7a) convey all information of the ability of the stationary phase to participate in solute-solvent intermolecular interactions. The r constant refers to the ability of the stationary phase to interact with solute n- or jr-electron pairs. The s constant establishes the ability of the stationary phase to take part in dipole-type interactions. The a constant is a measure of stationary phase hydrogen-bond basicity and the b constant stationary phase hydrogen-bond acidity. The / constant incorporates contributions from stationary phase cavity formation and solute-solvent dispersion interactions. The system constants for some common packed column stationary phases are summarized in Table 2.6 [68,81,103,104,113]. Further values for non-ionic stationary phases [114,115], liquid organic salts [68,116], cyclodextrins [117], and lanthanide chelates dissolved in a poly(dimethylsiloxane) [118] are summarized elsewhere. 

System constants derived from the solvation parameter model for packed column stationary phases at 121°C... 

Most of the stationary phase types in Table 2.8 were derived from popular packed column stationary phases and subsequently modified to allow for immobilization and improved thermal stability. Their selectivity equivalence can be ascertained by comparison of system constants for stationary phases of nominally similar chemical composition in Table 2.6 and 2.8 [125]. There are small differences in selectivity for... 

Some representative examples of packed column stationary phases belonging to categories (l)-(3) are summarized in Table 4. Hydrocarbons are used as low-selectivity liquid phases for separations of (mainly) low-polarity compounds by differences in their vapor pressure. Highly fluorinated liquid phases... 

The system constants for packed column stationary phases are summarized in Table 8. Classification of their properties by cluster analysis results in the connection dendrogram shown in Figure 4. Stationary phases with similar solvation properties are located next to each other and connected close to the left-hand side of the dendrogram. Stationary phases with no paired descendents are singular phases with properties that cannot be duplicated by other phases from the data set (Table 8). Classification results in six groups with three phases behaving... 

To extend the usefulness of packed columns, stationary phase materials have been mixed in varying proportions, and the proportion adjusted to enhance the selectivity for a specified set of target compounds (35). The pattern of peak retention times produced by the column can be adjusted within the range of patterns produced by the individual stationary-phase materials. The effects of each phase in the nfixtuie on the retention of the resulting peaks are additive if retention for each mixture component is expressed as its retention factor for the individual stationary phases and if the total volume of stationary phase is constant. 

Column. Packed with stationary phase containing 10 per cent by weight of... 

The chromatographic procedure may be carried out using (a) a stainless steel column (10 cm x 4.6 mm) packed with stationary phase C (3 pm) (Hypersil ODS in suitable), (b) as the mobile phase with a flow rate of 2 mL/min a 0.6% (w/v) solution of ammonium acetate in a mixture of 300 volumes of acetonitrile, 320 volumes of methanol and 380 volumes of water, and (c) a detection wavelength of 235 nm. 

Recent advances in column stationary phases are remarkable. High performance silica-based reversed-phase 3 to 5 jxm packing materials have been developed for biological sample separations... 

Some GC packings or stationary phases are sensitive to either or both oxygen and water. Because soil always contains both, it is important that care be taken with the analysis of soil air or soil extracts to make certain that they do not contain any components that will degrade the chromatographic column, which may cost between 500 and 1000. 

The most widely used support substance for the manufacture of packing materials in analytical HPLC columns is silica. Silica can be treated with organochlorosilanes or similar reagents to produce siloxane linkages of any derived polarity similar to what is done for GC columns (stationary phases). The most popular materials are octadecyl silane (ODS), which contains a carbon loading of CIS groups and octyl, which contains C8 groups materials such C2, C6, and C22 are also available. 

Chromatography column packed with stationary phase particles... 

Unger, K.K., du Fresne von Hohenesche, C., and Schulte, M. (2005) Columns, packings and stationary phases, in Preparative Chromatography, 1st edn (ed. H. Schmidt-Traub), Wiley-VCH Verlag GmbH, Weinheim, pp. 51-105. 

In adsorption and partition chromatography, a continuous equilibration of solute between mobile and stationary phases occurs. Eluent goes into a column and eluate comes out. Columns may be packed with stationary phase or may be open tubular, with stationary phase bonded to the inner wall. In ion-exchange chromatogra-... 

The use of hydrothermally formed retaining frits in capillary columns packed with stationary phase particles is an accepted limitation in CEC. The introduction of the frit to hold the packed bed is vital, yet introduces problems such as EOF and flow non-uniformities, compromised frit permeability [87], capillary fragility, increased likelihood of bubble formation [88] and a thermally induced modified frit surface chemistry which can detrimentally alter the chromatography [23]. Practical aspects to be considered include the appreciable effort and skill of the analyst who is required to repeatably manufacture capillaries of a particular phase and redevelop the fritting and packing methodology for each different stationary phase type. 

The assay of an IV formulation is performed using a liquid chromatographic method, which requires the following solutions. For solution (1), dilute a quantity of the intravenous infusion with sufficient mobile phase to produce a solution containing the equivalent of 0.05% w/v of ciprofloxacin. Solution (2) contains 0.058% w/v of ciprofloxacin hydrochloride EPCRS in mobile phase. Solution (3) contains 0.025% w/v of ciprofloxacin impurity C EPCRS (ethylenediamine compound) in solution (2). For solution (4), dilute 1 volume of solution (3) to 100 volumes with the mobile phase. The chromatographic procedure may be carried out using a stainless steel column (12.5 cm x 4 mm) packed with stationary phase C (5 mm) (Nucleosil C18 is suitable). The mobile phase is eluted at a flow rate of 1.5 mL/min, and consists of a mixture of 13 volumes of acetonitrile and 87 volumes of a 0.245% w/v solution of orthophosphoric acid (the pH of which has been adjusted to 3.0 with triethylamine). Analytes are detected on the basis of their UV absorption at 278 nm. The assay is not valid unless in the chromatogram obtained with solution (3), the resolution factor between the peaks due to ciprofloxacin and the ciprofloxacin impurity C is at least 1.5. 

As with any form of chromatography, the separating efficiency of capillary columns in gas chromatography is strongly dependent on the column stationary phase, carrier gas flow rate, and temperature. Because of the high separation efficiency of capillary columns, only a limited number of stationary phases can be substituted for the numerous phases used in most packed column applications. The choice of a stationary phase is commonly dictated by experience. A phase that has been successfully used by others is usually a good choice. Fre-... 

An HPLC system, shown schematically in Figure 2.1, consists of a solvent reservoir, which contains the eluent or mobile phse a pump, often called a solvent delivery system an injector through which the sample is introduced into the system without a drop in pressure or change in flow rate the analytical column, which is usually stainless steel and contains the solid packing or stationary phase and a suitable detector to monitor the eluent. 

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