title: Chemotrapping-atomic fluorescence spectrometric method as a field method for volatile arsenic in natural gas.
abstract: Volatile arsenic compounds in natural gas, existing in the form of trimethylarsine (TMAs), have been determined using gas cryo-trapping gas chromatography coupled to inductively coupled plasma-mass spectrometry (CT-GC-ICP-MS). The results from a number of different gas wells revealed a huge concentration spread ranging from below the detection limit of 0.2 up to 1800 microg/m(3) TMAs (as As) in the gas. Due to the toxicity and corrosive nature of these arsines, they need near real time monitoring via a method that can easily be implemented on site, i.e. during gas exploitation. Here, we introduce a novel method which utilises silver nitrate impregnated silica gel tubes for quantitative chemotrapping of trimethylarsine (TMAs) from a natural gas matrix. Subsequent elution with hot nitric acid followed by online photo-oxidation hydride generation atomic fluorescence spectrometry (HG-AFS) is used for the determination of TMAs gas standards in nitrogen and natural gas samples, respectively. The chemotrapping method was validated using CT-GC-ICP-MS as a reference method. The recovery of arsenic from nitrogen or natural gas matrix ranged from 85 to 113% for a range of 20 to 2000 ng As. Trapping efficiency was >98%, from the methods LOD of 20 ng to 4.8 microg (absolute amount As) with sample sizes of 0.02 and 2 L gas. Method performance was established by comparing the results obtained for eight natural gas samples containing between 1 and 140 microg As/m(3) with those achieved by the reference method (CT-GC-ICP-MS).
authors.affiliation: University of Aberdeen, College of Physical Sciences, Trace Element Laboratory (TESLA), Aberdeen, Scotland.
authors.forename: M Kalle
authors.initials: MK
authors.lastname: Uroic
authors.forename: Eva M
authors.initials: EM
authors.lastname: Krupp
authors.forename: Charlie
authors.initials: C
authors.lastname: Johnson
authors.forename: Jörg
authors.initials: J
authors.lastname: Feldmann
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001152:Arsenicals / Q000032:analysis*; D004784:Environmental Monitoring / Q000379:methods*; D005579:Fossil Fuels / Q000032:analysis*; D005615:Freezing; D008401:Gas Chromatography-Mass Spectrometry; D013050:Spectrometry, Fluorescence / Q000379:methods*
chemical_list: D000393:Air Pollutants; D001152:Arsenicals; D005579:Fossil Fuels; C009572:trimethylarsine