Niobium carbide as permanent modifier for silicon determination in petrochemical products by emulsion-based sampling GF AAS

The sample preparation was carried out by emulsion-based sampling, using about 200 mg of samples (crude oil, diesel or gasoline), 125 μL of hexane (only for crude oil) and 7.5 mL of Triton X-100 (20% v v−1). The mixture was stirred manually for few seconds, submitted to ultrasound bath for 30 min, and diluted to 25 mL with high-purity water. The combination of NbC as permanent modifier to avoid the formation of thermally stable SiC and 20 μg of Pd as co-injected chemical modifier to avoid losses of volatile silicon was mandatory for the success of the proposed method. In these conditions, the sensitivity of silicon was increased around six times and the relative standard deviation was decreased around 10 times. After heating program optimization, the pyrolysis and atomization temperatures were 1300 °C and 2600 °C, respectively. The limit of detection, limit of quantification and characteristic mass were, respectively, 2.6 μg L−1, 8.6 μg L−1 and 141 pg. The relative standard deviation was lower than 1% for 100 μg L−1 of Si. The accuracy was checked by the analysis of oil-based Si standards and the found values are in accordance with the reference values at 95% confidence level. Addition of 30 μg L−1 of Si in crude oil, gasoline and diesel samples resulted in recoveries ranging from 95% to 111%.