DryLab model

The DryLab model utilized in Waters AMDS has additional requirements The number of sample components should not exceed 12 peak area% should be greater than 1%. These requirements are necessary to achieve greater prediction accuracy only. Any discrepancies could be corrected manually in DryLab using the data entry screen by manually entering the retention of the components from the scouting runs (to assign the peaks with a certain number). DryLab has been used for the method development of model drug candidates... 

The DryLab modeling of this separation also indicated that it was especially sensitive to small changes in % MeCN and temperature. These results were incorporated into the method development procedure as recommendations for allowed variations in conditions. 

Only seven experimental runs are necessary for an isocratic procedure in order to obtain all of the required data to determine simulation models (DryLab models) for the four most important chromatographic parameters ... 

Figure 10-1. DryLab software version 3.0 modeling the separation of a mixture of naphthalenes. Resolution of the critical pair (the two peaks that elute closest together) is denoted as a function of time of gradient. Experimental runs are shown as sohd lines on the resolution map selected prediction is a dashed line.

Initial methods development should include an investigation of resolution as a function of temperature. The recommended minimum temperature is 40°C unless a lower temperature is required to meet the method objectives. DryLab can be used to model effect of temperature upon resolution. Four gradients should be run two gradients differing in gradient slope (shallow and steep gradient) and each at two different temperatures (e.g., 35°C and 50°C). 

Drylab Chromaiography Modeling Software. LC Resources. Walnut Creek, CA. 

Software DryLab (Rheodyne/LC A popular computer modeling 5,000 USD... 

HiPac (53) from Phase Separation is another commercially available software package. In several aspects this software is similar to DryLab, but its most important feature is that it can estimate the optimum mobile-phase conditions for the separation of the mixture at hand or only a selected number of peaks. Recently, ChromSword (commercially available from Merck, Germany) was introduced (34). It uses a retention mc el based on solvophobic theory. The input for this package can be the structural formulas of the solutes, the combination of structural formulas and retention data from a single run, or retention data from two runs. Data from additional runs are incorporated into the model, and prediction accuracy below 3% can be achieved under these circumstances. 

In the GC mode, two initial temperature-programmed runs conducted over the same temperature range (i.e., the same initial and final temperatures) at two different heating rates are required for initial input data. For the best combination of predictive range and accuracy, these rates should differ from one another by a factor of about 3. A measured value for and an average value of the column plate number must be entered as well. DryLab software then uses these input data to calibrate the model and consequently, simulating separations of other conditions. 

Optimal isocratic and/or gradient conditions are predicted by computer optimization software by retention time and peak width modeling, e.g., with DryLab (LC Resources, BASi Northwest Laboratory Services, Walnut Creek, CA, USA), LC Simulator (Advanced Chemistry Development, Toronto, Canada), or ChromSword (VWR International, Darmstadt, Germany). 

With the exception of the coltunn, any one of the selectivity conditions in Table 1 can be modeled, or two of them can be modeled simultaneously, by DryLab (if the column is changed, new calibration runs must be carried out). The number of experimental runs required for DryLab simulation varies from two to nine [21], depending on which selectivity variables are chosen. When a wide range in some condition (e.g., pH) is to be covered, additional runs can be carried out for improved predictive accuracy [20]. Additional modes are available for normal-phase and ion-exchange HPLC, as well as GC. The user can also create virtually any mode desired. 

Next, two DryLab calibration runs were carried out, as shown in Fig. 2 a spiked sample was used with gradient times of 15 and 90 min. Peak tracking by area matching and photodiode array showed that the separation of the peak of interest was not achieved in either run (Fig. 3). Also, significant changes in peak elution order were observed. Retention data from the two runs were modeled by DryLab to yield the resolution map of Fig. 4, for isocratic separation of the sample as a function of %B (i.e., % MeCN). In Fig. 4, only the resolution of peak 3 is... 

A best (interim) DryLab-predicted isocratic separation is shown in Fig. 16. Because of excess resolution in this separation, it is clear that a reduction in run time is possible with further changes in the conditions. The effects of shorter columns (10 cm instead of the original 15 cm) and higher flow rates (0.75 mL min as opposed to the original 0.45 mL min ) were modeled using DryLab, leading to the result shown in Fig. 17. The total mn time was reduced from about 9 min to less than 4 min, while maintaining adequate resolution between the peaks of interest... 

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