title: Optimized enrichment and purification of ferrocyanide for 13/12C and 15/14N isotope analysis of aqueous solutions.
abstract: The occurrence of ferrocyanide, Fe(CN)(6)(4-), in aqueous environments is of concern, since it is potentially hazardous. For tracing the source of ferrocyanide in contaminated water we developed a method that relies on the determination of the stable isotope ratios of (13)C/(12)C and (15)N/(14)N of this complexed cyanide (CN) after precipitating it as cupric ferrocyanide, Cu(2)[Fe(CN)(6)] · 7H(2)O. The precipitate was combusted and the isotope ratios were determined by continuous flow isotope ratio mass spectrometry. At first, ferrocyanide enrichment from synthetic water containing cyanide with known isotopic composition was studied by using six commercial anion-exchange resins. Five resins revealed a quick and complete sorption of ferrocyanide. A nearly quantitative desorption was achieved using NaCl solutions of 5 and 10% by weight for four resins. Subsequent determination of the δ(13)C(CN) and δ(15)N(CN) values of the ferrocyanide revealed that no significant isotope fractionation occurred during this procedure. These results were reproduced even in column experiments using larger water volumes. Potential interferences were also addressed. Sulfate in excess competes for exchange sites but can be precipitated as BaSO(4) prior to ferrocyanide enrichment. Non-cyanide carbon compounds may co-precipitate with cupric ferrocyanide, thus possibly modifying the isotope ratios. However, neither dissolved inorganic carbon nor highly soluble organic compounds did interfere with the method. Poorly soluble organics like BTEX and PAH can be eliminated by passing the samples through appropriate adsorber resins in a prior step. The proposed method is an excellent way of precise determination of the stable cyanide-carbon and cyanide-nitrogen isotope ratios in ferrocyanide-containing aqueous samples, which was successfully applied to four contaminated groundwater samples since measured aqueous isotopes ratios match those of corresponding cyanide-bearing solid wastes.
authors.affiliation: Lehrstuhl für Sediment- und Isotopengeologie, Institut für Geologie, Mineralogie und Geophysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany.
authors.forename: Ulrike
authors.initials: U
authors.lastname: Schulte
authors.forename: Jenny
authors.initials: J
authors.lastname: Weihmann
authors.forename: Tim
authors.initials: T
authors.lastname: Mansfeldt
mesh_terms: D000837:Anion Exchange Resins / Q000737:chemistry; D002247:Carbon Isotopes; D005295:Ferrocyanides / Q000302:isolation & purification*; D005374:Filtration; D007553:Isotope Labeling / Q000379:methods*; D009587:Nitrogen Isotopes; D009930:Organic Chemicals / Q000302:isolation & purification; D012965:Sodium Chloride / Q000737:chemistry; D012987:Soil / Q000032:analysis; D012995:Solubility; D012996:Solutions; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000302:isolation & purification; D018508:Water Purification / Q000379:methods*; D014881:Water Supply / Q000032:analysis
chemical_list: D000837:Anion Exchange Resins; D002247:Carbon Isotopes; D005295:Ferrocyanides; D009587:Nitrogen Isotopes; D009930:Organic Chemicals; D012987:Soil; D012996:Solutions; D014874:Water Pollutants, Chemical; D012965:Sodium Chloride