Journal of Chromatography A, 1355 (2014) 179–192 Contents lists available at ScienceDirect Journal of Chromatography A j o ur na l ho me page: www.elsevier.com/locate/chroma Particle size distribution and column efﬁciency. An ongoing debate revived with 1.9 m Titan-C 18 particles Fabrice Gritti a , David S. Bell b , Georges Guiochon a,∗ a Department of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA b Supelco Analytical, Bellefonte, PA 16823, USA a r t i c l e i n f o Article history: Received 15 April 2014 Received in revised form 6 June 2014 Accepted 10 June 2014 Available online 23 June 2014 Keywords: Particle size distribution Column efﬁciency Mass transfer mechanism Eddy dispersion Titan particles n-Alkanophenones a b s t r a c t The mass transfer mechanism in four prototype columns (2.1 and 3.0 × 50 mm, 2.1 and 3.0 × 100 mm) packed with 1.9 m fully porous Titan-C 18 particles was investigated by using two previously reported home-made protocols. The ﬁrst one was used to measure the eddy dispersion HETP of these new columns, the second one to estimate their intrinsic (corrected for HPLC system contribution) HETPs. Titan particles are fully porous particles with a narrow particle size distribution (RSD of 9.2%). The mean Sauter diameter (d Sauter = 2.04 m) was determined from Coulter counter measurements on the raw silica material (before C 18 derivatization) and in the absence of a dispersant agent (Triton X-100) in a 2% NaCl electrolyte solution. The results show that these RPLC Titan columns have intrinsic minimum reduced HETPs ranging from 1.7 to 1.9 and generate up to 290,000 plates per meter. The 3.0 mm i.d. columns are more efﬁcient than the 2.1 mm i.d. ones and short columns are preferred to minimize efﬁciency losses due to frictional heating at high speeds. This work also revealed that (1) the lowest h values of the Titan columns are observed at low reduced velocities ( opt = 5); (2) this is due to the unusually small diffusivity of analytes across the porous Titan-C 18 particles; and (3) the Titan columns are not packed more uniformly than conventional columns packed with fully porous particles. Earlier and recent ﬁndings showing that the PSD has no direct physical impact on eddy dispersion and column efﬁciency are conﬁrmed by these results. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The past and recent literature on the relationship between the efﬁciency of chromatographic columns and the particle size distri- bution (PSD) of their packing material is quite unanimous. Halasz and Naefe investigated the inﬂuence of various column parameters on peak broadening in HPLC for particles larger than 50 m [1]. They concluded that the efﬁciency of 2,6-xylidine was hardly inﬂu- enced by the width of the sieve fraction as long as it deviated from the arithmetic mean by less than approximately 40%. This result was later conﬁrmed by Done and Knox [2]. In the 1970s, Unger et al. [3] discussed the inﬂuence of the particle size (5–35 m) of mate- rials with various PSDs and particle shapes. They concluded that the column permeability and its efﬁciency were nearly unchanged when the mean particle diameter was kept constant. The relative standard deviations (RSDs) of the different sieve fractions were less than 25% for the smallest particle size (6 m) and larger than 10% for the largest size range (33 m). A few years later, Unger ∗ Corresponding author: Tel.: +1 865 974 0733; fax: +1 865 974 2667. E-mail addresses: guiochon@utk.edu, guiochon@ion.chem.utk.edu (G. Guiochon). and Messer [4] compared the performance of columns packed with spherical or irregular silica and alumina particles (1–10 m) with various size distributions. They observed no signiﬁcant difference in the minimum reduced plate heights. The RSDs of the various PSDs varied from 20% (10 m mean diameter) to 60% (2 m mean diam- eter). In the 1980s, Dewaele and Verzele [5] evaluated the impact of the PSD of the packing material on the plate height in LC. They prepared a series of packing materials by mixing 3 and 8 m parti- cles in different proportions. A linear increase in the plate number with increasing mass fraction of the 3 m particles was observed, showing that a wider particle size distribution had no inﬂuence on the column efﬁciency. More recently, Billen et al. [6] discussed the impact of the PSD on the performance of sub-2 m particles and concluded that it was not the width of the PSD but rather the presence of ﬁnes that greatly determines the chromatographic performance of packed columns. Finally, a series of columns were packed with different mass fractions of 3 and 5 m particles with a RSD of the PSDs adjusted between 17 and 43% but no impact of the RSD was observed on the reduced plate heights [7]. This study even suggested that the presence of a small amount of 3 m parti- cles amidst the larger 5 m ones or vice versa led to smaller h values than those measured for columns packed with only small or large particles. http://dx.doi.org/10.1016/j.chroma.2014.06.029 0021-9673/© 2014 Elsevier B.V. All rights reserved.