Influence of secondary interactions on high performance size exclusion chromatography. Application to the fractionation of landfill leachates

Abstract

Many authors undertook the chemical characterisation of the leachates generated by the municipal landfills. The review of the data of the literature (see [1]) shows that several separative and analytical techniques were primarily used i.e. the ultrafiltration, the liquid-liquid extraction, the permeation chromatography on Sephadex gels, the adsorption on Amberlite XAD resins, and the gas chromatography. This led us to use a different method: the high performance size exclusion chromatography (HPSEC).We carried out a preliminarily study [1], which showed that leachates from domestic wastes contain molecules which could be filed in two main groups according to their molecular weights: one constituted of molecules of AMW (Apparent Molecular Weight) lower than 1000 Da and the other one with molecules of AMW higher than 10000 Da. Few products of intermediate molecular weights are present. Simultaneous monitoring of the samples by UV absorbance, fluorescence and evaporative light scattering (ELSD) reveals the diversity of the physico-chemical characteristics of the separated compounds. A thorough spectrometric study [2] enabled us to validate the choice of excitation/emission couples characteristic of the substances so-called humic-type and protein-type compounds used in the first study. We also showed that the chromatographic elution of the molecules is biased by secondary interactions. So, in the present article we propose to study the influence of these interactions on chromatographic separation.The mechanism of steric exclusion is theoretically a purely entropic phenomenon, which warrants for the observed relation between the volume of elution and the hydrodynamic volume of the eluted molecule. One however notes experimental variations in retention times either due to adsorption (elution delayed) or exclusion (elution advanced). This is to say that interactions between the eluted molecules and the stationary phase modify the elution order of compounds with definite molecular weights. In aqueous solvents, very polar ionised groups are exposed at the water-soluble compounds surface and secondary enthalpic interactions are observed [3][4][5]. They are due to ion-exchange and ionexclusion effects, hydrophobic interactions and hydrogen bonds. The solute-support interactions are of course undesirable for the study of the molecular weight distribution of the molecules but they can be made profitable for the optimisation of their separation. These interactions were previously described [4,6,7] and it was shown that the choice of the eluent is particularly critical in aqueous size exclusion chromatography. It is not trivial to eliminate such interactions but they can be, at least, strongly reduced by judiciously choosing the eluent properties (pH, ionic strength, addition of organic co-solvent...) [7]. Sodium nitrate is often preferred for the elution of humic substances in HPSEC. At a 20 mM concentration in the eluent, the elution of the fulvic acids on both polymeric-and silica-based columns is weakly disturbed by the io...

Size Exclusion Chromatography for the Quantitative Profiling of the Enzyme-Catalyzed Hydrolysis of Xylo-oligosaccharides

“…However, our literature search illustrated in Table 1 showed that this was only done in a few of the references. Le Coupannec et al (36) also observed a slight alternation of the retention time in the chromatograms when using NaNO 3 and CH 3 COONH 4 as eluents for HPSEC. This could be due to the influence of the nature of the salt on the matrix pore and the compound size.…”

Monitoring WWTP performance using size-exclusion chromatography with simultaneous UV and fluorescence detection to track recalcitrant wastewater fractions

“…In absence of secondary interactions, longer elution time corresponds to smaller MW. Secondary interactions, such as adsorption on the column material, hydrophobic and electrostatic effects, lead to advanced or delayed elution that violates the mechanism of purely steric exclusion (Le Coupannec et al, 2000). While hydrophobic effects are important at high ionic strength of eluent, M A N U S C R I P T…”

“…5 the role of electrostatic effects (particularly, ion exclusion) increases with decrease of eluent ionic strength (Specht and Frimmel, 2000). Eluents of low ionic strength (2-20 mM) provide high chromatographic resolution for anionic compounds, however, elution of cationic compounds is delayed due to the ion exclusion (Le Coupannec et al, 2000). Eluents with high ionic strength may be undesirable because "macromolecule aggregation in wastewater will be destroyed with the addition of Na + , which can substitute divalent metal ions (such as Ca 2+ ) involved in extracellular polymeric substances bridging" (Guo et al, 2011).…”

“…Interestingly, ~40% of tyrosine-like fluorescing compounds in influent eluted outside the calibration range, while in effluent less than 20% of tyrosine-like fluorescing compounds demonstrated delayed elution. The late elution could be caused, for example, by specific interactions between wastewater components and the column material or by ion exclusion of cationic compounds (LeCoupannec et al, 2000).Most fractions simultaneously exhibited tyrosine-like, tryptophan-like, and humic/fulvic-like fluorescence, suggesting that protein-like and humic/fulvic-like matter eluted together. Humic and fulvic compounds are known to interact with proteins and other biomolecules and form various associations including covalent bonded structures(Arenella et al, 2014;Sutton and…”

Investigation of iodine bioavailability from chicken eggs versus iodized kitchen salt with in vitro method

“…2a. The effect can be explained with the influence of ionic interactions as the secondary separation mechanism [28,29].…”