Desenvolvimento de um vaporizador eletrotérmico para determinação direta de cloro em coque de petróleo por ICP-MS.

Abstract

In this work it was developed a vaporization system for petroleum coke samples for determination of chlorine by inductively coupled plasma mass spectrometry (ICP-MS). For that, it was developed an electrothermal vaporization chamber, a printed circuit board for temperature control and a software with graphical user interface for system operation. The vaporization of samples occurs by heating an incandescent lamp whose format allows the deposition of the samples directly on it. Using the software developed in LabVIEW® environment, the user determines the temperature of the lamp and the desired time, and can split the operation into several stages with different heating ramps. The software also allows to drive the solenoid valves for controlling the flow of argon gas and gases generated during the process. To drive the lamp and valves was developed a printed circuit board responsible for controlling power, which communicates with the computer through the USB port in a commercial interface board. During system calibration, several tests on samples of petroleum coke were performed to adjust the temperatures of pyrolysis and vaporization for chlorine, set at 350 °C and 900 °C respectively, adjusting the flow rate of carrier gas, set at 1.20 L min-1 and optimization of the mass of the sample, limited to 5 mg per sample. Also a certified reference sample of coal was used, whose concentration of chlorine is 32 mg g-1 (SARM 19). The detection limit calculated for chlorine using the system was 3.5 mg g-1. Thus, the system was considered adequate for the proposed determinations, and dramatically reduces the analysis time to approximately 2 min per test, minimizing risks of contamination, analyte losses and waste generation.