Repeatability of the efficiency of columns packed with sub-3 μm core–shell particles: Part III. 2.7 μm Poroshell 120 EC-C18 particles in 4.6 mm and 2.1 mm × 100 mm column formats

As part of an investigation of the column-to-column repeatability of the efficiency of columns packed with sub-3 μm shell particles, the parameters of the mass transfer kinetics of twelve columns packed with the same batch of 2.7 μm Poroshell 120 EC-C18 particles (Agilent Technologies, Little Fall, DE, USA) were sequentially measured, using columns provided by the manufacturers that were representative of the efficiency distribution given by the quality test control. The reduced longitudinal diffusion term (B) was measured using the peak parking (PP) method; the reduced solid–liquid mass transfer resistance term (C) was given by a combination of the PP results and the most accurate model of effective diffusion in ternary composite materials. The overall eddy diffusion term (A) was obtained by subtraction of these two HETP terms from the overall reduced HETP derived from the peak moments measured by numerical integration of the entire peak profiles. The results demonstrate that the dispersion of the column efficiencies is a result of the random nature of the packing process and the eddy diffusion term resulting from the lack of homogeneity of the column bed. At the highest reduced velocity achieved for small analytes, the relative standard deviations (RSD) of the eddy diffusion term for the 2.1 mm I.D. columns were ca. 3 and 11% (with average values heddy= 2.5 and 13.5) for naphthalene (k = 3) and uracil (k = 0), respectively. For the 4.6 mm I.D. columns, these RSDs were 5 and 13%, respectively, with average values heddy= 1.4 and 2.9. For insulin at reduced velocities as high as 160, the RSDs of the total reduced plate heights were 3 and 8% for the 2.1 and 4.6 mm I.D. columns, respectively.