Gradient elution mode

Normal-phase (NP) and reversed-phase (RP) liquid chromatography are simple divisions of the LC techniques based on the relative polarities of the mobile and stationary phases (Figure 4.10). Both NPLC and RPLC analysis make use of either the isocratic or gradient elution modes of separation (i.e. constant or variable composition of the mobile phase, respectively). Selection from these four available separation techniques depends on many variables but basically on the number and chemical structure of the compounds to be separated and on the scope of the analysis. 

In addition, the use of fast gradients elution mode has become the bioanalytical mainstream as a possible way to improve peak parameters (shape and symmetry) and to minimize method development time, especially for the multi-analytes methods. 

L. Kolafova, P. Jandera, E.C. Vonk, H.A. Claessens, Chromatographia 59,579, 2004 P. Jandera, Gradient elution mode, in Handbook of HPLC, 2nd edn, D. Corradini, T.M. Phillips, eds., this book. Chapter 5. 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

It is also possible to monitor a broad range of wavelengths without interrupting the flow in the column. This results in the full UV spectrum of the eluting mobile phase and provides a good means of identification of the analytes (Fig. 3.14). Such diode-array detectors (DAD) can be used in the gradient elution mode. Actually, they are frequently used in automated routine analysis. 

Hodges, R. S., Burke, T. W. L., and Mant, C. T. (1988). Preparative purification of peptides by reversed phase chromatography—sample displacement versus gradient elution modes. ]. Chromatogr. 444, 349-362. 

Gradient Elution. To change the retention volume of the copolymers of different composition, a gradient elution mode was required... 

HP-NPC can be performed on unmodified silica that separates analytes according to their intrinsic polarity. HP-NPC can also be operated in isocratic, step gradient, or gradient elution mode, where the retaining mobile... 

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