By applying viscosity and and surface measurements to the Floryand Fox eguation derived to describe macropolymers,Goshand Schnitzer(1980)depictedhumicmatter aslinearpolymers having size and shapes depending on ionic strengthandpH of solution and concentration of sample.GOSHANDSCHNITZERMODELlonic strength(M)plSampleoncentratior54.05x10-1x1025x1021x101X1036.58国的DOLow Conc中High Conecf4
By applying viscosity and and surface measurements to the Flory and Fox equation derived to describe macropolymers, Gosh and Schnitzer (1980) depicted humic matter as linear polymers having size and shapes depending on ionic strength and pH of solution and concentration of sample
Assuming humic matter to be a polydisperse macropolymericmixture,Cameron etal.(1972)employedultracentifugation bysedimentation velocity technigue,to determine the MW of a numberof fractions ofHA separated by Gel Permeation ChromatographyThe MWvalues werereported torange from102 to 10Dalton3·0,C2B6870B52·0B40-30Mffminfmin083B2oB1A2C3A11-010*105104107Molecularweight
Assuming humic matter to be a polydisperse macropolymeric mixture, Cameron et al. (1972) employed ultracentifugation by sedimentation velocity technique, to determine the MW of a number of fractions of HA separated by Gel Permeation Chromatography. The MW values were reported to range from 102 to 106 Dalton
WERSHAW'SMODEITo explain the evident surfactant properties of humicsubstances, and their capacity to solvate hydrophobiccontaminants,Wershaw (1994)proposed that humic substancesbe aggregates or micelles of amphiphilic molecules with polarand apolar tails as much as in cell membrane arrangements.However, he did not directly approched the molecular size ofthe aggregating moleculesUHydrophilic headHydrophobic part
Hydrophilic head Hydrophobic part WERSHAW’s MODEL To explain the evident surfactant properties of humic substances, and their capacity to solvate hydrophobic contaminants, Wershaw (1994) proposed that humic substances be aggregates or micelles of amphiphilic molecules with polar and apolar tails as much as in cell membrane arrangements. However, he did not directly approched the molecular size of the aggregating molecules
THESUPRAMOLECOLARSTRUCTUREExperimental results (HPSEC, NMR, ESI-MS) indicate thathumic substances,rather than being macropolymers, aresupramolecular self-associations of heterogeneous and relatively“"small" molecules stabilized by weak bonds (H-bonds, van derWaals,元-π, CH-元), which may be disrupted by small amounts oforganic acids.CH,COOH00O50502525Void VolumeVoidVolumeRetentionVolumeRetentionVolumeTotalVolumeTotal VolumeSIZE-EXCLUSIONCHROMATOGRAPHY
CH3 COOH Retention Volume Void Volume Total Volume 100 50 25 I n t e n s i t y ( m V ) Void Volume Total Volume Retention Volume 100 50 25 I n t e n s i t y ( m V ) THE SUPRAMOLECOLAR STRUCTURE Experimental results (HPSEC, NMR, ESI-MS) indicate that humic substances, rather than being macropolymers, are supramolecular self-associations of heterogeneous and relatively “small” molecules stabilized by weak bonds (H-bonds, van der bonds, van der Waals, π-π, CH-π), which may be disrupted by small amounts of organic acids. SIZE-EXCLUSION CHROMATOGRAPHY
PRINCIPLESOESE-EXCLUSIONCHROMATOGRAPHYMobilePhaseB.Fig.2.1.Schematic of an SEC separation showing theseparation of low ()andhighMw()polymers:Astartofseparation; B smaller molecules diffuseintoporousparticles,whilelargermoleDcules eluteinthe interstitial regions ofthe packec bed; C size separation iscompleted; D large molecules,whichsamplelesscolumnvolume,elutefirst:EE small molecules having access to bothinterstitial and pore volumes eiute later
PRINCIPLES OF SIZE-EXCLUSION CHROMATOGRAPHY