Canadian Journal of Pure & Applied Sciences

Abstract: Produced water is the aqueous component of crude oil and has not been previously characterized for noxious oxidation states: Cr3+/Cr6+ and As3+ /As5+. It is often returned to the environment where it could create an unwanted hazard. It remains unexplored in this context largely because standard HPLC techniques do not permit convenient simultaneous separation of Cr3+/Cr6+ and As3+/As5+ due to proximity of corresponding retention times. Our group has adapted a facile process for rapid elution and concurrent mass separation of all four species in an affiliated HPLC/ICP-MS system equipped with a dynamic reaction cell (DRC). Oxygen gas was circulated through the DRC to remove interferences and enhance detection of the eluted components, especially the arsenic constituents. The stationary phase consisted of a C8 deactivated silica based column (length 150 mm; internal diameter: 4.6 mm; particle size: 5 ?m); and the mobile phase was composed of a mixture of TBAH/EDTA in 2% methanol/water, adjusted to a pH of 7.2. The rate of elution was 1 mL/min; and recorded retention times (min) were: As3+: 1.81; As5+: 5.50; Cr3+: 1.83; and Cr6+: 5.74. The oxygen flow rate in the DRC was 0.7 mL/min. The Cr3+/ Cr6+ constituents were detected with m/z values of 52; the arsenic species coalesced with oxygen and were detected as adduct ions, AsO+, m/z, 91. Standard reference materials were deployed to test the competency of the analytical system. Typical recorded levels in the samples were: Cr3+: 0.5 – 20 mg/L; Cr6+/As3+/As5+: 1-5 ?g/L. Our results were evaluated in terms of the potential source of toxicity of produced water to the environment. The significance of the study to petroleum and environmental science is discussed.