Relative retention, resolution

Retention time Capacity factor Relative retention Resolution ... 

The variables that control the extent of a chromatographic separation are conveniently divided into kinetic and thermodynamic factors. The thermodynamic variables control relative retention and are embodied in the selectivity factor in the resolution equation. For any optimization strategy the selectivity factor should be maximized (see section 1.6). Since this depends on an understandino of the appropriate retention mechanism further discussion. .Jll be deferred to the appropriate sections of Chapters 2 and 4. 

Chromatographic system (See Chromatography <621 >.) The liquid chromatograph is equipped with a 230 nm detector and a 4.6 mm x 30 cm column that contains packing L7. The flow rate is about 2 mL/min. Chromatograph the Resolution solution and the Standard preparation, and record the peak responses as directed under Procedure the resolution, R, between the dibutyl phthalate and miconazole peaks is not less than 5, the tailing factor for the miconazole peak is not more than 1.3, and the relative standard deviation for replicate injections of the Standard preparation is not more than 2%. The relative retention times are about 0.7 for dibutyl phthalate and 1 for miconazole. 

Chromatographic system. (Follow the method described in the general procedure <621 >.) The gas chromatograph is equipped with a flame ionization detector and a 1.2 m x 2 mm column packed with 3% phase G32 on support S1A. The injection port, detector, and column temperatures are maintained at about 250, 300, and 250 °C, respectively, and helium is used as the carrier gas, flowing at rate of about 50 mL/min. The relative retention times for cholestane and miconazole nitrate are about 0.44 and 1, respectively. Chromatograph the Standard preparation, and record the peak responses as directed for procedure The resolution, R, between cholestane and miconazole nitrate is not less than 2 and the relative standard deviation of replicate injections is not more than 3%. 

Chromatographic system. The gas chromatograph is equipped with a flamioniza-tion detector and a 2 mm x 1.8 m glass column packed with 10% phase G34 on 80- to 100-mesh support SI A. The column temperature is maintained at about 150 °C, and the injection port and the detector block temperatures are maintained at about 250 °C. Dry helium is used as the carrier gas at a flow rate of about 40 mL/min. Chromatograph the Standard preparation, measure the peak responses, and calculate the ratio, Rs, as directed for procedure the relative retention times are about 0.5 for valproic acid and 1.0 for biphenyl the resolution, R, between valproic acid and biphenyl is not less than 3.0 the relative standard deviation for replicate injections is not more than 2.0%. 

Equation (2) shows that the resolution is a function of three different factors (1) the resolving power of the column as measured by the plate number that expresses the relative width of bands (2) the relative retention of the two compounds that measures how far apart the bands are from each other and (3) the magnitude of retention, as separation is a result of retention. The relative influence of these factors has been discussed by Snyder (72,13) in a form very easy to use in practice. 

On a column 125 cm long, operated at 160° C, these retention times (in minutes) were obtained air peak, 0 90, heptane, 1 22 and octane, 1-43. The base widths of the bands were 0-16 for heptane and 0-22 for octane. The relative retention and the resolution for these bands are ... 

M. T. Bowser, G. M. Bebault, X. Peng, and D. D. Y. Chen, Redefining the Separation Factor Pathway to a Unified Separation Science, Electrophoresis 1997,18, 2928. The conventional equation is resolution = ( )(i + J, where ct is relative retention, k 2 is the capacity factor for the more retained component, and k w is the average capacity factor for the two components. This expression is equivalent to (-y — 1) for closely spaced peaks for which... 

Fig. 12 High-performance liquid chromatographic resolution of the 9-anthrylmethyl esters of free fatty acids obtained from Heterosigma akashiwo cultured in axenic conditions. An aliquot (1/100 of 31 mg of phytoplankton) of the extract was injected. The peak of 20 5 corresponds to 746 ng. Unidentified peak with 0.42 in relative retention time with respect to 18 0. See text for chromatographic conditions.

The mass spectrometer must be operated in SIM mode. The 13C-analogs of isomers may be used as internal standards. The analytes are identified from then-relative retention times and characteristic masses. In low resolution MS, the characteristic masses for 2,3,7,8-TCDD are 320, 322, and 257. Use either 37C14-2,3,7,8-TCDD or 13C12-2.3.7.8-TCDD as an internal standard. The m/z for these two internal standards are 328 and 332, respectively. 

System suitability specifications and tests, Capacity factor (k ), Preci-sion/injector repeatability (RSD), Relative retention (a), Resolution (Rs),Tailing factor (T),Theoretical plate number (N)... 

Variation of Fluorescence Signal with Polarity of the Mobile Phase. A change in polarity of the mobile phase often aids the resolution of the pesticide from interfering co-elutants. However, the relative retention area for several chromatographic peaks obtained in the fluorescence mode of detection was found to vary as the mobile phase in the HPLC was changed. The data in Table 3 show the effects of common chromatographic solvents on the fluorescence of two pesticides. For maretin and o-phenyl-phenol, the relative fluorescence intensity, as measured in a spectrofluorometer, increased substantially as the polarity of the solvent increased. However, as shown for pyrazophos in... 

Figure 1.5 Influence of (a) the relative retention (o), (b) the (average) capacity factor (k) and (c) the number of theoretical plates (A/) on the resolution (Rv) according to eqn.(1.22). In each case the two other parameters are kept constant, k and N are assumed not to equal zero, and a not to equal one.

Reduced parameters, 66-69 Refractive index (RI) detector, 206-207 Regular solution, 49 Relative retention, 20-21, 22, 77 Repeatability, see Precision Reproducibility, see Precision Resolution, 17-19, 55 Response factors (detector), 104, 125 Response time, 94 Retardation factor, Rf, 71 Retention index of Kovats, 78 Retention ratio, 11, 12, 71 Retention time, 6, 9 Retention volume, 9, 75 adjusted, 10, 75 corrected, 62-63, 75 net, 63, 75 specific, 110 Reverse phase LC, 158 Rohrschneider/McReynolds constants, 137-140... 

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