ABSTRACT
In the simple isocratic HPLC elution mode, the chromatographic conditions are kept constant. Many complex samples contain compounds that differ widely in retention, so that HPLC in isocratic elution mode does not yield successful separation. If the isocratic conditions are adjusted for adequate retention of strongly retained solutes, some weakly retained components of complex samples may elute as poorly-if at all-separated bands close to the column hold-up time. On the other hand, if the operation conditions are adjusted so as to achieve satisfactory separation of weakly retained compounds, the elution of strongly retained sample components may take a very long time, their peaks may be broad, and their concentration in the efuent may be so low that the peak detection and integration becomes very difcult or even impossible. To solve this problem, the elution conditions can be changed according to a preset program during the elution.
