A chromatographic estimate of the degree of heterogeneity of RPLC packing materials. 1. Non-endcapped polymeric C30-bonded stationary phase

Journal Article · Sun Jan 01 00:00:00 EST 2006 · Journal of Chromatography A

DOI:https://doi.org/10.1016/j.chroma.2005.10.010· OSTI ID:989606

Gritti, Fabrice ^[1]; Guiochon, Georges A ^[2]

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1. University of Tennessee, Knoxville (UTK)
2. ORNL

A new chromatographic method estimating the degree of heterogeneity of RPLC packing materials is based on the results of systematic measurements of the adsorption data in a wide concentration range for selected probe compounds. These data are acquired by frontal analysis (FA), modeled, and used for the calculation of the adsorption energy distribution (AED). Four compounds were used, two neutral compounds of different molecular sizes (caffeine and phenol) and two ionizable compounds of opposite charges, 2-naphthalene sulfonate, an anion, and propranololium, a cation. This work was done on a C{sub 30}-bonded silica stationary phase (Prontosil-C{sub 30}), using the same aqueous mobile phase (30% methanol, v/v) for all compounds, except that sodium chloride (25 mM) was added to elute the ionizable compounds. All four adsorption isotherms have Langmuirian behavior. The AEDs are tri-modal for phenol, quadri-modal for caffeine. The total saturation capacity of the stationary phase is four-fold lower for caffeine than for phenol, due in part to its larger molecular size. The equilibrium constants on the low-energy sites of types 1 and 2 are eight-fold larger. These two types of sites characterize the heterogeneity of the bonded layer itself. The density of the high-energy sites of types 3 and 4 is higher for caffeine, suggesting that caffeine molecules can be accommodated in some hydrophobic cages into which smaller molecules like phenol cannot. These high-energy types of sites characterize the heterogeneity of the whole stationary phase (silica support included). The ionizable compounds have larger molecules than the neutral ones and, accordingly, a lower relative density of sites of type 2 to sites of type 1. A tri-modal and a quadri-modal energy distributions were observed for the 2-naphthalene sulfonate anion and the propranololium cation, respectively. The fourth types of sites measured and its unusually high equilibrium constant are most probably due to ion-exchange interactions between the non-endcapped ionized silanols and the propranololium ion. No such strong interactions are observed with the anionic compound.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 989606
• Journal Information: Journal of Chromatography A, Vol. 1103, Issue 2006; ISSN 0021-9673
• Country of Publication: United States
• Language: English

Related Subjects

10 SYNTHETIC FUELS
ADSORPTION
ADSORPTION ISOTHERMS
ANIONS
CAFFEINE
CAPACITY
ENERGY SPECTRA
ION EXCHANGE
METHANOL
PHENOL
PROBES
SATURATION
SILICA
SODIUM CHLORIDES
STRONG INTERACTIONS
SULFONATES
column reproducibility
monolithic column
adsorption isotherm
band profiles
frontal analysis
isotherm modeling
affinity energy distribution
multi-langmuir isotherm
phenol
caffeine