Chromatographic processes retention time

In chromatography, a series of signals from the detector output is registered as a chromatogram. The qualitative information is derived from the retention time, tms, which is determined by the chromatographic process. Retention time is also dependent on the thermodynamic properties of both the stationary phase... 

It is important to realize that many important processes, such as retention times in a given chromatographic column, are not just a simple aspect of a molecule. These are actually statistical averages of all possible interactions of that molecule and another. These sorts of processes can only be modeled on a molecular level by obtaining many results and then using a statistical distribution of those results. In some cases, group additivities or QSPR methods may be substituted. 

Manually processing each chromatographic peak is not only time and labor intensive but difficult to reproduce. To overcome these problems and to provide a consistent data format that was independent of retention time, a number of data-processing subroutines were automated to produce a single representative cellular protein spectrum. 

Gas chromatographic data was obtained on a Tracor Model 220 gas chromatograph equipped with a Varian Model 8000 autosampler. The analysis column was a 1.7 m "U column, 4 mm id, filled with 3% SP-2250 packing (Supelco, Inc., Bellefonte, PA) held at 200 C. The injection temperature was 250 and the nitrogen carrier gas flow rate was 60 mL/min. The detector temperatures were 350 for electron capture and 190 for flame photometric. Detector signals were processed by a Varian Vista 401 which gave retention times and peak areas. 

As readily observed in most chromatograms, peaks tend to be Gaussian in shape and broaden with time, where W, becomes larger with longer This is caused by band-broadening effects inside the column, and is fundamental to all chromatographic processes.The term, plate number (N), is a quantitative measure of the efficiency of the column, and is related to the ratio of the retention time and the standard deviation of... 

One of the important operational variables in CEC is the analyte—sorbent interaction. In reversed-phase separations (typical in CEC) the hydrophobicity of the stationary phase determines the selectivity of the separation, and retention can be controlled by adjusting the surface chemistry of the packing, composition of the mobile phase, and temperature. In contrast to HPEC, the CEC column plays a dual role in providing a flow driving force and separation unit at the same time hence electrophoretic and chromatographic processes are operational. The stationary phase chemistry is dealt with in detail in Section III on column technology. 

The uncertainty in the measurement of elution time / or elution volume of an unretained tracer is another potential source of error in the evaluation of thermodynamic quantities for the chromatographic process. It can be shown that a small relative error in the determination of r , will give rise to a commensurate relative error in both the retention factor and the related Gibbs free energy. Thus, a 5% error in leads to errors of nearly 5% in both k and AG. An analysis of error propagation showed that if the... 

The reports from the integrator consist of retention time and sample amount for each integrated peak. These are transmitted to a small computer. The integrator has the capacity to process up to 250 peaks in a run. However, because of the limited memory space of the computer, we had to decrease the number of peaks processed. Chromatographic runs with more than 150 peaks were reduced to 150 peaks by elimination of those with the smallest area. The reduced reports were then stored on tape. 

Activity coefficients at infinite dilution, of organic solutes in ILs have been reported in the literature during the last years very often [1,2,12,45,64, 65,106,123,144,174-189]. In most cases, a special technique based on the gas chromatographic determination of the solute retention time in a packed column filled with the IL as a stationary phase has been used [45,123,174-176,179,181-187]. An alternative method is the "dilutor technique" [64,65,106, 178,180]. A lot of y 3 (where 1 refers to the solute, i.e., the organic solvent, and 3 to the solvent, i.e., the IL) provide a useful tool for solvent selection in extractive distillation or solvent extraction processes. It is sufficient to know the separation factor of the components to be separated at infinite dilution to determine the applicability of a compound (a new IL) as a selective solvent. 

Analytical. Samples were chromatographed on a Hewlett-Packard 5880A gas chromatograph which was fitted with a 30M fused silica capillary column (DBS) and an automatic sampler. The GC was interfaced to a Hewlett-Packard 3354 Laboratory Automation System (LAS). Raw data was automatically transferred to the LAS where peaks were selected by retention time, integrated and stored in a processed file. Processed data was then transferred... 

Figure 2.8—Simulated distillation of lubricating oil (Polvwax). Using a column that can operate at high temperatures, a correlation is made between retention times and boiling temperatures for a series of oligomers. The sample to be distilled is then run under the same chromatographic conditions. Software using the chromatogram reproduces a distribution curve identical to that which would be obtained from the mixture if it were distilled, a much longer process (document SGE 712-0546 and -0547).

ANALYSIS TIME. If possible we like to perform the chromatographic separation in a minimum time. Time is important in analysis but it is particularly important in process chromatography. Analysis time is based upon the solute component which is more readily sorbed. Using the equation for determination of retention time,... 

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