Mobile phase table

Select mobile phases for HPSEC based on their ability to dissolve the sample and their compatibility with the column. Zorbax PSM columns are compatible with a wide variety of organic and aqueous mobile phases (Table 3.4), but analysts should avoid aqueous mobile phases with a pH greater than 8.5. As mentioned earlier, select mobile phases that minimize adsorption between samples and silica-based packings. Sample elution from the column after the permeation volume indicates that adsorption has occurred. If adsorption is observed or suspected, select a mobile phase that will be more strongly adsorbed onto the silica surface than the sample. For example, N,N-dimethyl-formamide (DMF) is often used for polyurethanes and polyacrylonitrile because it eliminates adsorption and dissolves the polymers. When aqueous mobile phases are required, highly polar macromolecules such as Carbowax can be used to coat the silica surface and eliminate adsorption. Table 3.5 provides a list of recommended mobile-phase conditions for some common polymers. 

Mobile phase Table II for details of mobile phases all contain polyethylene oxide... 

The great versatility of HPLC lies in the fact that the stability of the chemically bonded stationary phases used in partition chromatography allows the use of a wide range of liquids as a mobile phase without the stationary phase being lost or destroyed. This means that there is less need for a large number of different stationary phases as is the case in gas chromatography. The mobile phase must be available in a pure form and usually requires degassing before use. The choice of mobile phase (Table 3.6) is influenced by several factors. 

These detectors obviously require a careful selection of solvents utilized as mobile phases. Tables of UV cutoffs are readily available. UV-VIS detectors can be used with gradients. An interesting feature is the use of derivatives of the spectra. 

Hexane /2-Propanol—based Mobile Phases (Table 5)... 

CSPs (CTA-I and CTA-II) have inverse selectivity for Troger s base and trans-1,2-diphenyloxirane racemates. These characteristics of CTA CSPs are responsible for good chiral resolution of small cychc carbonyl compounds [42]. In 2001 Aboul-Enein and Ah [63] observed the reversed order of elution of nebivolol on a Chiralpak AD column when ethanol and 2-propanol were used separately as the mobile phases. Table 1 presents selectivity data for the polysaccharide-based CSPs. Okamoto et al. [42] observed that the introduction of a methyl group at the para position of cellulose tribenzoate results in a dramatic shift of the structural selectivity toward aromatic compounds with larger skeletons, and its selectivity was rather similar to that of cellulose tricinnamate. 

Kg values. Kg values give information about the affinity of the solute for the surfactant covered stationary phases. The first observation indicates that, in spite of this surfactant-coverage, the polar nature of the bonded stationary phases is preserved the order of increasing KgW values of toluene is the same order as the decreasing stationary phase-polarity i.e. silica CN Cl C8 C18. The K values of toluene, with SDS mobile phases, were slighty lower than those with CTAB mobile phases (Table VI). 

Examples of optimizations in HPLC using the simplex approach can be found in [28,84]. In [28] the mobile phase composition for the chiral separation of (6/ )- and (65)-leucovorin on a BSA (bovine serum albumin) stationary phase is optimized by means of a variable-size simplex. Three factors were examined, the pH of the mobile phase buffer, the ionic strength of the buffer and the percentage of 1-propanol in the mobile phase. Table 6.19 shows the experimental origin, the initial step size and the acceptable limits for the factors. The criterion optimized is the valley-to-peak ratio (Section 6.2). The points selected and the results are pre.sented in Table 6.20 and... 

Verpoorte and Baerheim Svendsen reported the analysis of a series of alkaloids on microparticulate silica gel using diethyl ether or chloroform with various percentages of methanol as mobile phase (Table 2.4). The optimum wavelength of detection for fixed wavelength detectors of 254 and 280 nm for the alkaloids investigated were also reported, c... 

Jane et al. obtained unsatisfactory results for analysis of cocaine and related compounds when using silica gel or octadecyl modified silica gel as stationary phase. However, good separations and peak performance were obtained with a chemically bonded dimethylsilyl phase and methanol - aqueous 0.1 M ammonium nitrate (2 3)(pH 4.3) as mobile phase (Table 4.6). 

In all these calculations we need to know the viscosity of the mobile phase. Table 2.2 contains the data for the solvents commonly used in HPLC. Most mobile phases, however, are mixtures of solvents. For nonpolar solvents, one can estimate the viscosity of a mixture by linear interpolation between the viscosities of the component solvents. This is not true for aqueous mixtures due to the strong association of polar solvents. Since aqueous mixtures are the mobile phases for reversed-phase chromatography, it is important to know their viscosity. Figure 2.9 ows the viscosity of the aqueous mixtures of the polar organic solvents commonly used in reversed-phase chromatography. Note that the water-alcohol mixtures exhibit a pronounced viscosity... 

Two mobile-phase compositions of H O/CHjCN (80 20, vol/vol) and 0.10 MNaNOj/CHjCN (80 20, vol/vol) were used for SEC-viscometry of partially hydrolyzed grades (32). PEO, PEG, and PSC were used for column calibration, and universal calibration was observed (29). Molecular weights by SEC-viscometry for grades of high, medium, low, and superlow molecular weight compare favorably those from SEC-LALLS, especially with the H O/CHjCN mobile phase (Table 6). It is suspected that the nonsalt mobile phase works better to eliminate the hydrophobic interactions and maximize the size exclusion mechanism (32). Intrinsic viscosity values calculated from viscometry for the two acetonitrile mobile-phase compositions and from Ubbelohde viscometry in HjO/CH CN, are also summarized in Table 6. 

Chromatographic systems have been developed for the reversed-phase TLC separation of lipophilic vitamins on RP-18 as stationary phase. A mixture of lipophilic vitamins (A acetate, E, E-acetate, and D3) was separated using acetonitrile-benzene-chloroform (10 10 1, v/v) as mobile phase (Table 3). The applied chromatographic conditions do not permit the separation of vitamin E and vitamin E-acetate. Derivative spectrometry was used to determine vitamin A acetate in mixtures of other lipophilic or water-soluble vitamins. Spectrophotometric analysis of lipophilic vitamins enables determination of vitamin A-acetate in the presence of vitamins E, E-acetate, and D3 and also C, Bi, and nicotinamide. 

Perisic-Janjic, Petrovic, and Hadzic described a method for the quantitative separadrm of vitamin A acetate and A palmitate by thin-IayCT chromatography on starch, cellulose, and talc impognated with parafiin oil using acetone-concentrated acetic add (3 2, vAr) as the mobile phase (Table 1). 

Allethrin D-allethrin has eight isomers (2 = 8), four cis (C, D, E, and F) and four trans (A, B, G, H) isomers. Mancini et al. (2004) separated cisitrans isomers from each other on an achiral silica HPLC column using n-hexane tert-butyl methyl ether (96 4) (v/v) as the mobile phase (Table Cl, Appendix C). The trans isomers were separated (G, H, A, B, respectively) from each other on a CHIRAL-CEL OJ using n-hexane-tert-butyl methyl ether (90 10) (v/v). This same colunm was used to separate the cis isomers (F, D, C, and E, respectively) using n-hexane isopropanol (99.3 0.7) (v/v). Kutter and Class (1992) were able to separate the trans allethrin isomers on a chiral p-cyclodextrin RP-HPLC column, but were unable to separate the cis isomers. 

CC is used mainly in the separation of a mixtore of carotenoids at semipreparative or preparative scale, although subsequently TLC is required. The choice of a stationary phase in which the carotenoid mixture is adsorbed and separated depends on its selectivity and nonreactivity with the pigments or mobile phase. Table 6.6 shows some of the stationary phases most commonly used in CC of carotenoids. Pigment... 

The use of silver nitrate as an impregnating agent on the layer was compared with results obtained by adding silver nitrate solution to the mobile phase (Table 8.8). A study was made with respect to the variation of ARp with the concentration of silver nitrate, methanol, and orthoboric acid. 

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