1-s2.0-S001670370201044X-main

1-s2.0-S001670370201044X-mainPIIS0016-7037(02)01044-XProton-bindingstudyofstandardandreferencefulvicacids,humicacids,andnaturalorganicmatterJASOND.RITCHIEandE.MICHAELPERDUE*SchoolofEarthandAtmosphericSciences,GeorgiaInstituteofTechnology,Atlanta,GA30332-0340,USA(ReceivedSeptember17,2001;acceptedinrevisedformMay6,2002)Abstract—Theacid–basepropertiesof14standardandreferencematerialsfromtheInternationalHumicSubstancesSociety(IHSS)wereinvestigatedbypotentiometrictitration.Titrationswereconductedin0.1MNaClunderanitrogenatmosphere,averaging30minfromstarttofinish.Concentrationsofcarboxylgroupsandphenolicgroupswereestimateddirectlyfromtitrationcurves.TitrationdatawerealsofittoamodifiedHenderson-Hasselbalchmodelfortwoclassesofproton-bindingsitestoobtain“bestfit”parametersthatdescribeproton-bindingcurvesforthesamples.Themodelwaschosenforitssimplicity,itseaseofimplementationincomputerspreadsheets,anditsexcellentabilitytodescribetheshapesofthetitrationcurves.ThecarboxylcontentsoftheIHSSsamplesarei