Retention time, adjusted corrected

Total retention time absolute retention time Adjusted retention time Corrected retention time... 

Qualitative HPLC methods, using area percent, are used to monitor the disappearance of starting material and the formation of byproduct. Without the inclusion of an internal standard and the calculation of response factors, it is not possible to establish with certainty whether all of the starting material can be accounted for. An internal standard must be stable in the reaction mixture, must not co-elute with any of the components, and must be stable in the mobile phase. Ideally, the internal standard has a retention time about half that of the total analysis time. Internal standardization is extremely useful for kinetic studies. Added to the reaction vessel, samples that are withdrawn at various times will contain identical concentrations of internal standard, and chromatograms can be directly compared or adjusted to identical scales to correct for variation in injection volume. 

To achieve maximum reproducibility you must make these decisions instead of leaving them to the machine. You will have to do a methods development project. TUrn off the automatics, shoot a sample, adjust a variable, and then repeat until you have it right. When setting variables manually, we first set the peak width followed by slope rejection and then noise rejection. If peak width is correct, the print gap, left when the integrator prints the retention time, will fall half way down the backside of the peak. If it falls closer to the... 

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... 

By this procedure, it is very likely that peaks corresponding to the same compound will be compared. A mass spectral identification is commonly needed to validate the correspondence of the standards. Also, the standards chosen for adjusting retention times should be spread in the chromatogram, and the extremes should bracket the retention times to be corrected. 

The proposed competitive adsorption model was implemented and used to calculate the band profiles of cyclopentanone with mobile phases of different compositions. One more adjustable parameter, an equilibrium constant for additional interactions, was introduced in order to match calculated and experimental retention of cyclopentanone. Figure 15.3 compares some calculated and experimental band profiles of cyclopentanone for mobile phases containing different concentrations of methanol in the mobile phase. In general, the agreement observed with either methanol or acetonitrile is good. However, like as any other complicated model, there are many parameters which must be determined by fitting the experimental data to the model and stiU, at the end, the calculated retention times of the solute(s) must be adjusted using a last empirical parameter in order to match the experimental retention times. There are no independent ways to verify that these parameters are correct. Therefore, in practice, the use of a more simplified model remains preferable. 

Adjusted retention time Jr, also known as corrected retention time, takes into account the dead time of the column see retention time and dead time. 

Corrected retention time see adjusted retention time. 

Mobile-phase hold-up time it is also equal to the retention time of an unretained compound Peak elution time Adjusted retention time Corrected retention time Temperature in general (always in Kelvin)... 

The capacity factor k is essentially a corrected retention time (Equation [3.18]) that takes into account variations in mobile phase flow rate and thus provides a more robust indicator of analyte retention for a given combination of stationary and mobile phases. As is a unique property of a given solute A for a given stationary-mobile phase combination, the adjusted (corrected) retention volume V,a (Equation [3.15] (or the corresponding retention time) can be used as a tag for analyte identification. Thus the precision and accuracy of measurement of Vja become important and depend on those of the measurement of flow rate U since in practice retention times rather than volumes are the measured quantities. In response to this limitation of the V,a parameter, the capacity ratio of a solute (k) ) was defined as the ratio of its distribution (partition) coefficient to the phase ratio (Vm/V s) of the column with respect to analyte A ... 

If the volumetric carrier gas flow rate (at the column exit) is measured and multiplied by the retention time, the retention volume, Vjj, is obtained. The adjusted retention volume, V, is the retention volume corrected for the void volume (or mobile phase holdup) of the column. It is obtained by simply subtracting the retention volume of an unretained solute (V ) ... 

Adjust the valve to RESET (forward flow) and inject 1.0 pL of a blend containing approximately 5 % each of benzene, ethylbenzene, o-xylene, and 2-hexanone in /sooctane. This mixture is used to set the valve timing, therefore, the exact concentration need not be known. Alternatively, the calibration mixture can be used for this test. Determine retention time in seconds at which benzene and ethylbenzene start to elute as measured by Detector B. Subtract 6 s from each of these and call these times to BACKFLUSH, Tl and T2, respectively. The correct time for Tl and T2 is just prior to the elution of benzene and ethylbenzene from the TCEP precolumn. 

Identification of a component in a sample relies principally on its retention on the column under a particular combination of chromatographic conditions. The retention time of a compound is defined as the time from injection to the time of maximum elution of the peak. In some instances this time is corrected to take into account the time for an inert gas to pass through the column and is then known as the adjusted retention time. This is necessary when considering relative retentions and in the calculation of the partition ratio, which is the ratio of the time spent by the solute in the liquid phase to that in the gas phase. 

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