Application of the general height equivalent to a theoretical plate equation to size exclusion chromatography. Study of the mass transfer of high-molecular-mass compounds in liquid chromatography

The mass transfer of nonretained, high-molecular-weight polystyrene standards in a chromatographic column packed with 4-mu m-diameter silica particles for SEC (average pore size 80 angstrom) and eluted with tetrahydrofuran was investigated. The HETPs of nine polystyrene standards (MW 560, 760, 1780, 3680, 6400, 13 200, 19 300, 31 600, and 90 000) and of ethylbenzene were measured by the method of moments. These HETPs were accounted for by a general HETP equation previously derived for the mass transfer of low-molecular-weight compounds in RPLC (Gritti, F.; Guiochon, G. Anal. Chem.2006, 78, 5329.). The best fit between the experimental and the theoretical HETPs allowed the estimation of the internal restricted diffusion coefficients of the polymers. The internal diffusion coefficients of the polystyrene standards were also measured, using the peak parking method. Both methods give comparable results and show that the restriction diffusion coefficient gamma K-p(D) decreases linearly with increasing logarithm of the polymer mass, from 0.56 for Log MW = 2.0 to 0 for Log MW = 4.8. Interestingly, the C term or limit slope of the high-velocity branch of the HETP curve passes through a maximum (highest mass-transfer resistance) for a polymer mass of 10 kDa. This maximum is well accounted for by the theoretical expression of the trans-particle mass-transfer contribution.