Which Columns Should Be Used, and How Do I Use Them

First of all, we need to distinguish between whether all the analytes to be determined and all the analytical issues are known, or if there is the possibility that unknown impurities are present. 

When our analytes and our analytical goal are known, then we can select the column directed toward this aim. If, for example, we want to separate organic acids differing primarily in the chain length of the aliphatic rest, that is, in then-hydrophobic selectivity, then it is best to try a classical endcapped, hydrophobic reversed phase, because this provides the methylene selectivity necessary for this problem. 

So if we have information on the analytes to be separated, then we can use this for clever selection of the column to be used. 

If we have to clarify the heterogeneity of an unknown sample, the sample must be examined on various columns with orthogonal selectivity to ensure that a possible co-elution is not overlooked. Selection of these columns is best orientated on the key characteristics of the colunms, which were considered in Section 4.4. 

If the separation does not work on a classical reversed phase, then the type of stationary phase must be radically changed. A change to a classical packing from a different manufacturer is only successful in isolated cases. The column with which 

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