Strategies for the determination of trace and toxic elements in pitch: Evaluation of combustion and wet digestion methods for sample preparation

• Metals determination in pitch by inductively coupled plasma optical emission spectrometry.
• Sample preparation methods based on combustion and wet digestion were evaluated.
• Diluted acid solutions were required for analytes absorption using MIC method.

Pitch is a complex matrix and hard to be digested. In this way, some sample preparation methods (wet digestion and combustion) were investigated for subsequent determination of Ba, Ca, Cd, Fe, Mg, Pb, Sr, V and Zn using plasma-based techniques as well as direct analysis by X-ray fluorescence (XRF). Among the investigated sample preparation methods, dry ashing and microwave-induced combustion (MIC) shown similar results for some analytes, but significant losses for Cd, Pb and Zn were observed when dry ashing was used. Thus, MIC was chosen once a diluted solution (3 mol L−1 HNO3) was suitable for analytes absorption, up to 400 mg of pitch could be digested and no analyte losses were observed. Accuracy of MIC was evaluated by analysis of a standard reference material of Green Petroleum Coke (NIST 2718). In addition, a comparison with results obtained by XRF and MIC was performed and no statistical difference was observed. Thus, the proposed MIC method can be considered as suitable for the digestion and further elements determination in pitch.

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