New theoretical advances in high-performance liquid chromatography

2 New theoretical advances in high-performance liquid chromatography 

Beds of porous spherical particles are generally applied in chromatography. However, when the sample contains particles such as cell debris, etc. the sample has to be pretreated before injection, making the separation process longer. Expanded beds using beads of different sizes and densities overcome this difficulty. 

In order to evaluate the efficacy of the expanded bed technique the plate height (HETP), plate number (N), resolution (Rs), Bodenstein number (Bo), particle Peclet number (Pep) and axial dispersion coefficient (DJ have been calculated and compared with the corresponding values of a traditional HPLC column. N can be expressed by 

The chromatographic parameters discussed above were calculated for packed beds (increased dispersion and bed length), and for expanded beds with moderate, higher and lower dispersion. The results indicated that the corresponding separation parameters of packed beds and expanded beds are commensurable, therefore, expanded beds can be successfully employed in liquid chromatography even in the case of trace analysis of synthetic dyes in waste water and sludge [75], 

Novel general expressions were developed for the description of the behaviour of the height equivalent of a theoretical plate in various chromatographic columns such as unpacked (open capillary), packed with spherical nonporous particles and packed with spherical porous adsorbent particles. Particles may have unimodal or bimodal pore size distribution. The expression describing the mass balance in open capillaries is 

---