Sample preparation strategies for petroleum cokedigestion and further cerium and lanthanumdetermination by DSN-ICP-OES

Abstract

The determination of cerium and lanthanum in petroleum coke samples by inductively coupled plasmaoptical emission spectrometry coupled to a desolvating nebulizer system (DSN-ICP-OES) is proposed forthefirst time after studying the following sample preparation methods: microwave-assisted digestion(MW-AD) in medium and high pressure systems and microwave-induced combustion (MIC). MW-AD ina medium pressure system was not suitable for digestion of petroleum coke even when using a lowsample mass (up to 100 mg). Both MIC and MW-AD in a high pressure system were considered suitablefor petroleum coke digestion, but MIC was preferable in view of the possibility of using diluted acid(2.5 mol L 1HNO3) to digest 400 mg of sample and obtaining lower residual carbon content (RCC)values (below 0.1% instead of approximately 25% for MW-AD). The use of MW-AD required a dilutionstep (with a factor of four) to minimize the interference in analyte determination by DSN-ICP-OES.Accuracy was evaluated by comparing the results with those obtained by neutron activation analysis (anagreement of more than 94% was obtained) and also analyzing spiked samples (recoveries in the rangeof 88 to 102% were achieved).