DryLab prediction

Figure 8-48. (Top) Drylab-predicted chromatogram versus (bottom) verification i...

Fig. 2.9 Diagram showing (a) Drylab predicted, and (b) Actual separation for the pharmaceutical, SB-243213 and its related substances.

The accuracy of Drylab, based on the above relationships, has been analyzed in several publications [15-21], and comparisons of separation vs. DryLab predictions have been reported in dozens of other papers, many of which are summarized in Ref. [13]. In most cases, the accuracy of resolution predictions is of the order of 10%, which is usually more than adequate. Expressions such as Eqs. (2) and (3), which are suitable for predicting retention as a function of certain conditions, require only two experimental runs for DryLab implementation. Other variables, such as pH or buffer concentration, require three or more runs, in which cases a cubic spline fit to the data can be used for predictive purposes. 

Fig. 5. Laboratory Example 1 (see Fig. 2) DryLab-predicted separation at 36% acetonitrile.

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... 

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... 

Alternatively, the results from the gradient runs for each sample can be inputted into Drylab, ACD, or Chromsword for further optimization (see Sections 8.5.6.11). For the predicted experimental conditions (i.e., gradient slope, temperature, flow rate), if desired selectivity and resolution can be obtained, an experiment can be run for verification. The peak purity for the main analyte (MS and DAD detection) should be checked in the verification run. If the desired selectivity and/or the target analyte are not spectrally homogeneous, go to Step 6, Figure 8-37. 

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.

For optimising two parameters at a time, one of the simplest, and easy to use computer software packages is DryLab, produced and marketed by LC Resources. Data from just two runs is used to predict both isocratic and gradient conditions. Usually the two runs are gradients in which the % organic component in the mobile phase is varied with time. The peak... 

ChromSword Auto Software incorporated into Waters AMDS. Useful tool for optimizing isocratic and gradient methods and for predicting optimum column configurations. Similar to DryLab and can also work 14,000... 

Figure 8.12. A DryLab color-coded resolution map simulated from data from Figure 8.10 for column optimization. The simulated chromatogram at T = 40°C and tG = 18min was predicted for a 75-mm-long, 3.5-mm Symmetry C8 column. It showed excellent resolution and run time <22 min.

Ch iges column conditions (column dimensions, particle size and flow rate) d predicts separation for any column condition Drylab, ENHANCER 165... 

Changes gradient conditions and predicts separation fa any gradient condition Drylab 153, 165,166... 

Many of these software systems work (particularly for Drylab ) by using mathematical algorithms to predict separations for a number of other conditions after a few experimental runs have been performed. Typical predictions are made for changes made to the mobile phase conditions, temperature, isocratic or gradient separations, or changes to the column conditions (e.g. column dimensions, particle size and flow rate). The references listed in Table 2.3 provide more specific descriptions of each type of software system. 

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. 

For evaluation of the predicted chromatograms DryLab uses a resolution map, which with measurements at, for example, two columns temperatures or differing pH is three dimensional. Gradients are shown on a graphic interface, where %B and can be changed with the mouse. The gradient editor allows entry... 

Figure 3.23 After entering the retention time in Figures 3.1 and 3.2, with DryLab the Resolution Map and the predicted isocratic chromatogram at 65.95% MeOH can be seen. The predicted retention times agree very well with those of Figure 3.3.

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. 

Predictions of bandwidth by DryLab require an estimate of the plate number N for each band, which can be provided by any of three options. First, DryLab can calculate a value of N based on mobile phase composition, temperature, column... 

Initial DryLab resolution map and predicted gradient separation. 

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