Microwave-assisted ultraviolet digestion of petroleum coke for the simultaneous determination of nickel, vanadium and sulfur by ICP-OES

A method for the simultaneous determination of Ni, V and S in petroleum coke by inductively coupled plasma optical emission spectrometry (ICP-OES) after microwave-assisted ultraviolet digestion (MW-UV) in closed vessels was proposed. Digestion was performed using electrodeless discharge lamps positioned inside quartz vessels and turned on by microwave radiation. The following parameters were evaluated: HNO3 concentration (15mL of 1, 4, 7, 10 or 14.4molL−1), volume of H2O2 (30%, 1 or 3mL), sample mass (100, 250 or 500mg) and heating time (40 or 60min) with or without the use of UV lamps. Digestion efficiency was evaluated by the determination of the residual carbon content (RCC) in digests. Using UV lamps lower RCC was obtained and the combination of 4molL−1 HNO3 with 3mL of H2O2 and 60min of heating allowed a suitable digestion of up to 500mg of petroleum coke (RCC< 21%). The agreement with the reference values for Ni, V and S (obtained by digestion of petroleum coke by microwave-induced combustion) and with a certified reference material of petroleum coke was between 96 and 101%. The proposed method was considered as advantageous when compared to American Society for Testing and Materials method because it allowed the simultaneous determination of Ni, V and S with lower limit of detection (0.22, 0.12 and 8.7µgg−1 for Ni, V and S, respectively) avoiding the use of concentrated nitric acid and providing digests suitable for routine analysis by ICP-OES. [Display omitted] •Microwave and UV radiation were combined for the first time for digestion of petroleum coke.•High sample masses (up to 500mg) were digested using the MW-UV method.•MW-UV method allowed the use of diluted acids for digestion of petroleum coke.•Simultaneous determination of Ni, V and S in digests was possible to be performed by ICP-OES.