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

Abstract

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 4more » 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.« less

Authors:
 [1];  [2]
  1. University of Tennessee, Knoxville (UTK)
  2. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
989606
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chromatography A; Journal Volume: 1103; Journal Issue: 2006
Country of Publication:
United States
Language:
English
Subject:
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

Citation Formats

Gritti, Fabrice, and Guiochon, Georges A. A chromatographic estimate of the degree of heterogeneity of RPLC packing materials. 1. Non-endcapped polymeric C30-bonded stationary phase. United States: N. p., 2006. Web. doi:10.1016/j.chroma.2005.10.010.
Gritti, Fabrice, & Guiochon, Georges A. A chromatographic estimate of the degree of heterogeneity of RPLC packing materials. 1. Non-endcapped polymeric C30-bonded stationary phase. United States. doi:10.1016/j.chroma.2005.10.010.
Gritti, Fabrice, and Guiochon, Georges A. Sun . "A chromatographic estimate of the degree of heterogeneity of RPLC packing materials. 1. Non-endcapped polymeric C30-bonded stationary phase". United States. doi:10.1016/j.chroma.2005.10.010.
@article{osti_989606,
title = {A chromatographic estimate of the degree of heterogeneity of RPLC packing materials. 1. Non-endcapped polymeric C30-bonded stationary phase},
author = {Gritti, Fabrice and Guiochon, Georges A},
abstractNote = {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.},
doi = {10.1016/j.chroma.2005.10.010},
journal = {Journal of Chromatography A},
number = 2006,
volume = 1103,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}
  • In a previous report, the heterogeneity of a non-endcapped C{sub 30}-bonded stationary phase was investigated, based on the results of the measurements of the adsorption isotherms of two neutral compounds (phenol and caffeine) and two ionizable compounds (sodium naphthalene sulfonate and propranololium chloride) by frontal analysis (FA). The same method is applied here for the characterization of the surface heterogeneity of two new brands of endcapped C{sub 18}-bonded stationary phases (Gemini and Sunfire). The adsorption isotherms of the same four chemicals were measured by FA and the results confirmed by the independent calculation of the adsorption energy distribution (AED), usingmore » the expectation-maximization (EM) method. The effect of the length of the bonded alkyl chain was investigated. Shorter alkyl-bonded-chains (C{sub 18} versus C{sub 30}) and the end-capping of the silica surface contribute to decrease the surface heterogeneity under the same experimental conditions (30% methanol, 25 mM NaCl). The AEDs of phenol and caffeine are bimodal with the C{sub 18}-bonded columns while they are trimodal and quadrimodal, respectively, with a non-endcapped C{sub 30}-bonded column. The 'supersites' (adsorption energy >20 kJ/mol) found on the C{sub 30}-Prontosil column and attributed to a cation exchange mechanism completely disappear on the C{sub 18}-Gemini and C{sub 18}-Sunfire, probably because the end-capping of the silica surface eliminates most if not all the ionic interactions.« less
  • The difference in adsorption behavior between a conventional monomeric endcapped C{sub 18} stationary phase (3.43 {micro}mol/m{sup 2}) and an endcapped polymeric RP-Amide phase (3.31 {micro}mol/m{sup 2}) was investigated. The adsorption isotherms of four compounds (phenol, caffeine, sodium 2-naphthalene sulfonate, and propranololium chloride) were measured by frontal analysis (FA) and the degree of heterogeneity of each phase for each solute was characterized by their adsorption energy distributions (AED), derived using the Expectation-Maximization method. The results show that only certain analytes (phenol and 2-naphthalene sulfonate) are sensitive to the presence of the polar embedded amide groups within the RP phase. Their bindingmore » constants on the amide-bonded phase are significantly higher than on conventional RPLC phases. Furthermore, an additional type of adsorption sites was observed for these two compounds. However, these sites having a low density, their presence does not affect much the retention factors of the two analytes. On the other hand, the adsorption behavior of the other two analytes (caffeine and propranololium chloride) is almost unaffected by the presence of the amide group in the bonded layer. Strong selective interactions may explain these observations. For example, hydrogen-bond interactions between an analyte (e.g., phenol or naphthalene sulfonate) and the carbonyl group (acceptor) or the nitrogen (donor) of the amido-embedded group may take place. No such interactions may take place with either caffeine or the cation propranololium chloride. This study confirms the hypothesis that analytes have ready access to locations deep inside the bonded layer, where the amide groups are present.« less
  • A radiochemical study of the irreversible adsorption of proteins on commercial reversed-phase HPLC packing materials is reported. The conditions of study are similar to those used in HPLC separation of protein. The effects of the amounts and contact time of two proteins, ovalbumin and cytochrome c, are reported. Additional results include the effect of column pretreatment with protein, silanophilic, mobile-phase blocking agent, and type of packing material on the extent of irreversible adsorption. The loss process is shown to be at least biphasic and the mechanisms of loss distinct for different proteins.
  • Proteomics analysis based-on liquid chromatography (LC), particularly reversed-phase LC (RPLC), is widely practiced; however, cutting-edge LC performance variations have generally not been adopted even though their benefits are well established. The two major reasons behind this general underutilization are: 1) uncertainties surrounding the extent of improvement (e.g., proteome coverage), and 2) the lack of availability of automated, robust, and convenient LC instrumentation. Here, we describe an automated format 20K psi gradient nanoscale LC system that was developed to provide improved separations and sensitivity for proteomics (and metabolomics) applications. The system includes on-line coupling of micro solid phase extraction for samplemore » loading and allows emitters for electrospray ionization to be readily replaced. The system uses 40 to 200 cm X 50 µm i.d. fused silica capillaries packed with 1.4- to 3-µm porous C18-bonded silica particles to obtain chromatographic peak capacities of 1,000-1,500 for complex peptide and metabolite mixtures. This separation quality allowed high confidence identification of >12,000 different peptides from >2,000 distinct Shewanella oneidensis proteins (~ 40% of the proteins predicted for the S. oneidensis proteome) in a single 12-h ion trap tandem mass spectrometry (MS/MS) analysis. The reproducibility was >87% for proteins identified between replicates. The protein MS/MS identification rate average exceeded 10 proteins per minute, e.g., 1,207 proteins were identified in 120 min through assignment of 5,944 different peptides. For a human blood plasma sample that was not depleted of the most abundant proteins, 835 distinct proteins were identified with high confidence in a single 12-h run. A single run with accurate mass MS detected >5,000 different compounds from a metabolomics sample.« less