Espectrometria de absorção atômica com tubo aquecido na chama e amostragem direta de sólidos para determinação de manganês e níquel em coque de petróleo

Abstract

A solid sampling flame furnace atomic absorption spectrometry (SS-FF-AAS) system was developed in this work for Mn and Ni determination in petroleum coke. The proposed solid sampling system was made in quartz, with two perpendicular tubes (T-shaped tube), adapted on the burner. Determination was made using an atomic absorption spectrometer with deuterium background corrector, using an air + acetylene flame and a single slot burner. Sample pellets up to 62 mg were introduced into the quartz device cell with a movable hollow quartz piston. When the sample pellet reaches the end of quartz cell, in the presence of oxygen flow, it quickly burns and the combustion products are transferred to the upper slot tube where the absorption atomic process happens. Calibration step was performed using aqueous standards applied directly on high purity graphite pellets and different masses of petroleum coke certified reference material (CRM). The results obtained for Mn and Ni using proposed SS-FF-AAS were compared to those obtained by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry after sample decomposition step by microwave assisted acid digestion (high pressure) and microwave induced combustion resulting in agreement higher than 96%. In addition, the agreement for Mn and Ni in CRM (coal and petroleum coke) was 96.3 ± 8.7% and 98.2 ± 3.0%, respectively. The relative standard deviation was lower than 9% for both analytes. Characterist masses were 18.3 ± 1.8 ng for Mn and 14.7 ± 1.4 ng for Ni and limit of detection were 0.64 and 0.82 μg g-1 for Mn and Ni, respectively. The throughput was 9 determinations per hour, including drying, weighing and pressing. The proposed SS-FF-AAS system can be applied for Mn and Ni determination in petroleum coke, combining high sample throughput, precision and accuracy.