doi:10.1016/j.chroma.2006.09.075 
Copyright © 2006 Elsevier B.V. All rights reserved.
Experimental evidence of the influence of the surface chemistry of the packing material on the column pressure drop in reverse-phase liquid chromatography
Fabrice Grittia, b and Georges Guiochona, b, 
, 
aDepartment of Chemistry, University of Tennessee, Knoxville, TN 37996-1600, USA
bDivision of Chemical Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6120, USA
Received 3 May 2006;
revised 6 September 2006;
accepted 20 September 2006.
Available online 13 October 2006.
References and further reading may be available for this article. To view references and further reading you must
purchase this article.
Abstract
The permeabilities of six columns packed with different packing materials (neat silica, C1 endcapped silica at 3.92 
mol/m2, C18 bonded and endcapped silica with 0.42, 1.01, 2.03, and 3.15 
mol/m2 of C18 bonded chains) were measured. All these materials derive from the same batch of spherical particles, 5 
m in diameter. The columns have the same tube inner diameter (
=0.460±0.003 cm) and length (L=15.000±0.003 cm). The experimental conditions were the same, flow-rate (Fv=1.000±0.003 mL/min) and temperature (295 K). Nevertheless, it was found that the column permeability decreases significantly, by about 25%, from the neat silica column to the one packed with the highest density of C18-bonded silica (3.15 
mol/m2). The results measured on two duplicate columns were very reproducible. Accurate (±0.5 %) measurements of the hold-volumes with concentrated and dilute solutions of 
showed that the columns had all nearly the same external porosity. The result cannot be explained by the error made on the volume of the column tube either as it was measured accurately for all the columns. The residual explanation is that the interstitial velocity distribution between the packed particles depends on the chemical nature of the external surface of these particles.
Keywords: RPLC; C18 bonding density; External porosity; Internal porosity; Total porosity; Permeability; Silica-C18; Endcapping
Fig. 1. Injection of 3 
L of three potassium nitrate (KNO3) solutions at concentrations of 0.178, 0.0178, and 0.00178 g/L on the six columns used in this work. Mobile phase: methanol:water, 50:50 (v/v); flow rate, 1 mL/min; T=295 K. Note the anti-langmuirian shape of all the peak profiles when the highest concentration is injected. Note, also, the more distorted shape of the large peak with the neat silica column.
Fig. 2. Measurement of the column pressure drop at different flow rates on the two duplicate columns A (empty symbols) and B (full symbols) for each type of column (silica, endcapped silica, endcapped C18-silica). Mobile phase: methanol:water, 25:75 (v/v). Note the excellent reproducibility of the column permeability between the two duplicate columns and the continuous increasing column pressure drop as the C18 surface coverage increases.
Fig. 3. Same as in Fig. 2, except the mobile phase is a mixture of acetonitrile and water (30:70, v/v), the silica column was not used, and only one flow rate was used (1 mL/min). Again, note the increase of the pressure drop as the surface coverage increases and the excellent reproducibility of the result between duplicate columns A and B. The increase of pressure drop is certain (+25%).
Fig. 4. Plot of the pressure drop measured with the duplicate columns A. Same experimental conditions as in Fig. 1. Note that the column pressure drop increases by about 35% when switching the neat silica column to the C18-silica column (2.03 
mol/m2).
Fig. 6. Plot of the actual external porosities (empty stars) measured by injecting 3 
L of potassium nitrate (0.00178 g/L) with the experimental error arising from the column tube volume standard deviation (±0.34%) and the elution time reproducibility of the nitrate anion 
(±0.5 %). Note that the expected (Kozeny–Carman relationship, full stars) and the experimental porosities significantly differ. No obvious correlation exist between the increasing pressure drop and the column external porosity.
Fig. 7. Plots of the relative difference between the pressure drop of the columns studied and the column packed with neat silica particles. Three different solvents were used (1-propanol, 2-propanol, and methanol), at different concentrations, as indicated in the legend.
Fig. 8. Same as in Fig. 5, except the mobile phase composition, methanol:water, 20:80 (v/v).
Fig. 9. Same as in Fig. 6, except the mobile phase composition, methanol:water, 20:80 (v/v).
Table 1.
Physico-chemical properties of six prototypes columns provided by the manufacturers (Waters)
a Measured from B.E.T. experiments.
b Measured from elemental analysis.
Table 2.
Measurements of the lengths and external diameter of the six columns used in this work
The precision of the caliper meter is 20 
m.
Table 3.
Measurements of the corrected (from extra-column volume contribution, 0.041 min) retention time of 
Mobile phase composition: methanol:water, 50:50 (v/v); flow rate, 1 mL/min; four consecutive injections.
Table 4.
Same as in Table 3, except the mobile phase composition, methanol:water, 20:80, v/v, and seven consecutive injections
In addition, the measurement of the corresponding pressure drop during the elution of potassium nitrate is given.
Abstract
Purchase PDF (642 K)
E-mail Article
Add to my Quick Links
Cited By in Scopus (6)
Purchase PDF (398 K)
