Column switcher, screening

Moreover, the effect of pH on a particular compound s retention needs to be determined first before exploring the retentivity and selectivity of different columns. The strategy and choice of the optimal pH for analysis was discussed in Chapter 4 and is further reinforced in the case studies within this chapter. After the optimal pH is chosen for the separation and the gradient has been optimized on a particular column and the optimal selectivity still has not been achieved between critical pairs, then a column screening can be performed. For method column screening, generally columns with 10-cm or 5-cm X 3.0-mm i.d. could be used that are packed with 3-pm particles. Implementation of a column switcher that can use six different types of stationary phases such as two types of C18 from different vendors, phenyl, two polar embedded, and pentafluorphenyl is suggested. 

Step 6 Screen additional columns/mobile phases with the optimized ".pH of the aqueous phase use AMDS or column Switcher. ... 

Step 6 Screen Different Columns/Mobile Phases Using an Automated Method Development System or Column Switcher. If the desired selectivity is not obtained or the peak is not spectrally homogeneous from Step 5, then different columns (two to six) and mobile phases can be screened using a column switcher. The typical mobile phases that could be screened include acetonitrile, methanol, and acetonitrile/methanol mixtures using the same "pH... 

With the advent of column switchers and more reproducible alternative column materials, it is now quite feasible to screen multiple pH values—for example, at high, medium, and low pH—using scouting gradients in order to choose the column and pH at which to perform further optimization experiments. This is a particularly tempting scenario when few or no chemical structures are available for the synthetic by-products or degradation products in the sample, or when samples are particularly complex. Recently there has been considerable development on systems for selection of optimal pH and type of column concomitantly [28]. 

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