Method development and validation for sulfur determination via CS molecule in petroleum green coke by high resolution continuum source molecular absorption spectrometry

Development and validation of a method for determination of sulfur via CS molecule in petroleum green coke samples by high resolution continuum source molecular absorption spectrometry (HR-CS MAS) is the aim of this work. The protocol adopted for the method validation followed criteria based on international guidelines. Optimizations and determination of the analyte in the samples were carried out at the wavelength 258.0330 nm, at the same spectral interval of the analytical line of Tl. Slurry prepared using Triton X-100 (0.05% v/v) without the use of HNO3, is proposed as a simple and fast sample treatment. Chemical modifier KOH (1.0% m/v) was important to promote the formation and stabilization of CS molecule. Pyrolysis and Vaporization temperatures were optimized using different compounds, ammonium sulfate, l-cysteine monohydrochloride and thiourea aqueous solutions, and also certified reference material, NIST 2718, and petroleum green coke. Compromise temperature conditions were 1000 °C and 2600 °C, for pyrolysis and vaporization, respectively. Aqueous calibration with thiourea presented the best condition and was chosen for the determination of the analyte. The obtained concentrations of sulfur in coke samples were between 6.20 mg g− 1 and 9.40 mg g− 1. The following parameters were evaluated as validation protocol: accuracy, precision, linearity, limits of detection and quantification, sensitivity, selectivity, robustness, working range and measurement uncertainty. Weighted least square (WLS) method was employed to estimate LOD and LOQ, since it leads to lower final uncertainty. The evaluation of the validation parameters, especially the measurement uncertainty, confirmed the satisfactory performance of the method.