Sulfur determination using the SiS diatomic molecule via HR-CS GF MAS and direct analysis of solid samples: A...

In this work, a simple and reliable method was proposed for sulfur determination in different matrices using the diatomic molecule SiS via high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GF MAS) and direct analysis of solid samples. This investigation was carried out using six sulfur standard solutions, Na₂S, Na₂SO₄, BeSO₄, thiourea, l-cysteine and sulfamic acid, and nine certified reference materials (CRMs). All measurements were performed using the SiS analytical line at 282.910 nm with 400 μg Zr as permanent modifier and 20 μg Si in basic media as molecule forming reagent. The optimized pyrolysis and vaporization temperatures were 1200 and 2000 °C, respectively. The investigated sulfur sources presented similar analytical signals and statistically equal A_int values for the SiS molecule. Calibration curves with aqueous sulfur standard solutions were used to achieve the limits of detection (LOD) and quantification (LOQ) and the characteristic mass (m₀) of 8.8, 29 ng mg^-1 and 9.8 ng, respectively, and to determine sulfur in the CRMs. Considering that the investigated wavelength range contained multiple SiS lines, the LOD (2.5 ng mg^-1), LOQ (8.4 ng mg^-1), m₀ (1.0 ng) and the working range (0.008-2.5 μg) were improved by using ten SiS lines (30 pixels) for the measurements. Despite differences in the CRM matrices, the SiS molecule was successfully employed to determine their sulfur concentrations, which were in agreement with the certified values at a confidence level of 95% through Student or Welch t-tests. Therefore, a simple, versatile and reliable method using the SiS molecule was developed to perform sulfur determination in a great variety of sample matrices via HR-CS GF MAS and direct analysis of solid samples.