The development of a digestion procedure for the determination of metals in gum obtained from deposits in internal combustion engines by ICP-OES

The accurate determination of metals in gum (deposits found in internal combustion engines) is strongly influenced by a selection of the right sample digestion method. The difficult and heterogeneous nature of this kind of sample, and its unpredictable reaction behavior are the major obstacles in getting correct analytical results. The studies were implemented with one sample called “reference sample”. Two digestion procedures were tested in this work. The dry ashing procedure was followed by another dissolution procedure with HF and heating, in order to complete the dissolution of the ash in the samples. The process was performed in 36 h. The second digestion procedure was implemented in closed system (pressurized) with 2 mL of HNO₃ and 2 mL of H₂SO₄. This last one presented a reduction of 80.5% time-consuming in relation to the first one (dry ashing). Al, Ca, Cd, Cr, Cu, Fe, K, Mg, Na, Ni, Pb, Si, and Zn were determined in 14 samples of gum by ICP-OES. The wet closed system digestion procedure showed efficiency in the Cr, Cu, Fe, K, Ni, Pb, Si, and Zn determination. The correlation matrix results contribute to the characterization studies of the gum formation process, as well as the corrosion of the motor parts and fuel quality control.