DryLab calibration runs

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... 

The starting conditions included use of an aqueous buffer and acetonitrile, a 250 X 3 mm, 3 pm particle Cjg column, a flow rate of 0.6 mL min , and UV detection at 200 nm. Four DryLab calibration runs with varying gradient time and temperature were selected (20—40% MeCN in 15 min or 60 min, with a temperature of 25 °C or 45 °C). Previous experience with similar compounds helped to narrow the gradient range. 

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. 

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. 

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