Petrochemical samples can be very diverse. Most fuel and oil samples when dissolved in the proper solvent have very little background interference. Thus successful ashing can be achieved at low temperatures in a minimal amount of time. In such cases a variety of elements including relatively volatile species like arsenic, lead and cadmium can be easily determined.
For samples containing low volatility organic constituents and/or particulate matter dilution is necessary. Whenever this situation is encountered furnace conditions should be carefully optimized to obtain the maximum analyte signal and minimum background signal. Background signal should be decreased by an increase in the ashing temperature. When the ashing temperature is too high, however, analyte may be lost during ashing thus decreasing the analyte signal. The maximum ashing temperature has to be determined empirically, it can vary extensively depending on the form of the element and matrix.
Different types of samples have characteristic background absorbance profiles depending on the wavelength at which the background is determined and the nature of the background. Figure 1 shows the background profile vs ashing temperature for 30 ml of a 1g engine oil sample dissolved in 100 ml of diisobutyketone (DIBK) and the maximum ashing temperature for each element determined in the dissolved sample.