title: NOM and alkalinity interference in trace-level hexavalent chromium analysis.
abstract: Three analytical methods were evaluated for hexavalent and trivalent chromium analyses in the presence of natural organic matter (NOM) and alkalinity. Each method was tested using a simulated tap water with 1 μg L(-1) Cr(VI) and 0.8 μg L(-1) Cr(III) and several concentrations of NOM and/or alkalinity. An ion chromatograph with post column reaction cell conforming to USEPA Method 218.7 could accurately quantify Cr(VI) in the presence of up to 8 mg CL(-1) NOM and up to 170 mg L(-1) as CaCO3 alkalinity, and no oxidation of chromium was observed when 0.8 μg L(-1) Cr(III) was also present. A high-performance liquid chromatography coupled with inductively coupled plasma (HPLC-ICPMS) method and a field speciation method were also evaluated. Each of these methods was unaffected by the presence of alkalinity; however, the presence of NOM created issues. For the HPLC-ICPMS method, as the concentration of NOM increased the recovery of Cr(VI) decreased, resulting in a 'false negative' for Cr(VI). However, for the field speciation method, Cr(III) was complexed by NOM and carried through the ion exchange column, resulting in a 'false positive' for Cr(VI).
authors.affiliation: Virginia Tech, USA. Electronic address: jparks@vt.edu.
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Parks
authors.affiliation: Utah State University, USA.
authors.forename: Laurie
authors.initials: L
authors.lastname: McNeill
authors.affiliation: Virginia Tech, USA.
authors.forename: Marc
authors.initials: M
authors.lastname: Edwards
mesh_terms: D002119:Calcium Carbonate / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002852:Chromatography, Ion Exchange / Q000379:methods*; D002857:Chromium / Q000032:analysis*; D005189:False Positive Reactions; D013058:Mass Spectrometry / Q000379:methods*; D009930:Organic Chemicals / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D009930:Organic Chemicals; D014874:Water Pollutants, Chemical; D002857:Chromium; C074702:chromium hexavalent ion; D002119:Calcium Carbonate
keywords: Alkalinity; Chromium; HPLC; ICPMS; Ion chromatography; Organic carbon