Factors chromatographic

Figure 4-59. Effect of hexafluorophosphate concentration on analyte retention, peak efficiency, N(ii/2), and tailing factor. Chromatographic conditions Column Zorbax Eclipse XDB-C8. Mobile phase 90% 0.1 v/v% phosphoric acid + xPFe [1-25 mM] 10% acetonitrile flow rate, l.OmL/min temperature, 25°C analyte load, Ijxg wavelength, 254 nm. (Reprinted from reference 153, with permission.)...

PharmPrint descriptors substructure descriptors ( pharmacophore-based descriptors) phase capacity ratio = capacity factor —> chromatographic descriptors... 

Fig. 7.3. Van t Hoff plots of capacity factors. Chromatographic conditions column, Partisil 1025 ODS (250 mmX4.6 mm I.D.) mobile phase, 0.05 M KH2PO4 flow rate, 1 ml/min temperature, 25° C detection, UV at 254 nm. Reproduced from Horvath et al. (1976), with permission.

The sensitivity is very good for nickel and vanadium but for these metals for which distribution data would be of great value, the chromatographic process is the lirniting factor, heavy molecules are not eluted from the column with the exception of some porphyrins. This detector can be used to supply H/C and S/C profiles for hydrocarbon cuts with the chromatograph operating in the simulated distillation mode. 

In a chromatographic analysis of low-molecular-weight acids, butyric acid elutes with a retention time of 7.63 min. The column s void time is 0.31 min. Calculate the capacity factor for butyric acid. 

The relative selectivity of a chromatographic column for a pair of solutes is given by the selectivity factor, a, which is defined as... 

In the same chromatographic analysis for low-molecular-weight acids considered in Example 12.2, the retention time for isobutyric acid is 5.98 min. What is the selectivity factor for isobutyric acid and butyric acid ... 

Now that we have defined capacity factor, selectivity, and column efficiency we consider their relationship to chromatographic resolution. Since we are only interested in the resolution between solutes eluting with similar retention times, it is safe to assume that the peak widths for the two solutes are approximately the same. Equation 12.1, therefore, is written as... 

Finally, solute A s capacity factor is eliminated using equation 12.11. After rearranging, the equation for the resolution between the chromatographic peaks for solutes A and B is... 

To determine how the height of a theoretical plate can be decreased, it is necessary to understand the experimental factors contributing to the broadening of a solute s chromatographic band. Several theoretical treatments of band broadening have been proposed. We will consider one approach in which the height of a theoretical plate is determined by four contributions multiple paths, longitudinal diffusion, mass transfer in the stationary phase, and mass transfer in the mobile phase. 

A variable-size simplex optimization of a gas chromatographic separation using oven temperature and carrier gas flow rate as factors is described in this experiment. 

Because volatility is such an important factor in GC, the chromatographic column is contained in an oven, the temperature of which can be closely and reproducibly controlled. For very volatile... 

The separating power of a chromatographic process arises from the development of many theoretical plates to achieve adsorption equiUbrium within a column of moderate length. Even though the separation factor between two components may be small, any desired resolution may be achieved with sufficient theoretical plates. 

Potency of hGH preparations is quantitatively deterrnined, in terms of mass per vial, by one or more chromatographic procedures (50). Biopotency is calculated from the mass-based potency using a conversion factor, typically 3 lU/mg. Traditionally a bioactivity assay using hypophysectomized rats has been used to determine potency however, the imprecision of this assay has resulted in its use only as a semiquantitative indicator of bioactivity (1), sometimes referred to as a bioidentity test. 

Preferably, high pressure Hquid chromatography (hplc) is used to separate the active pre- and cis-isomers of vitamin D from other isomers and allows their analysis by comparison with the chromatograph of a sample of pure reference i j -vitainin D, which is equiUbrated to a mixture of pre- and cis-isomers (82,84,85). This method is more sensitive and provides information on isomer distribution as well as the active pre- and cis-isomer content of a vitamin D sample. It is appHcable to most forms of vitamin D, including the more dilute formulations, ie, multivitamin preparations containing at least 1 lU/g (AOAC Methods 979.24 980.26 981.17 982.29 985.27) (82). The practical problem of isolation of the vitamin material from interfering and extraneous components is the limiting factor in the assay of low level formulations. 

The first observation of the enantioselective properties of an albumin was made in 1958 (28) when it was discovered that the affinity for L-tryptophan exceeded that of the D-enantiomer by a factor of approximately 100. This led to more studies in 1973 of the separation of DL-tryptophan [54-12-6] C22H22N2O2, on BSA immobilized to Sepharose (29). After extensive investigation of the chromatographic behavior of numerous racemic compounds under different mobile-phase conditions, a BSA-SILICA hplc column (Resolvosil-R-BSA, Macherey-Nagel GmvH, Duren, Germany) was... 

Purity. Gas chromatographic analysis is performed utilizing a wide-bore capillary column (DB-1, 60 m x 0.32 mm ID x 1.0 //m film) and a flame ionization detector in an instmment such as a Hewlett-Packard 5890 gas chromatograph. A caUbration standard is used to determine response factors for all significant impurities, and external standard calculation techniques are used to estimate the impurity concentrations. AHyl chloride purity is deterrnined by difference. 

When the adsorption equihbrium is nonlinear, skewed peaks are obtained, even when N is large. For a constant separation-factor isotherm with R < 1 (favorable), the leading edge of the chromatographic peak is steeper than the trailing edge. Wmen R > 1 (unfavorable), the opposite is true. 

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