A systematic look at the carbon monosulfide molecule and chemical modifiers for the determination of sulfur by HR-CS GF MAS

Abstract

This work describes an adequate method for the stabilization of three forms of sulfur (ionic, saturated, and unsaturated), with different chemical modifiers (Zr, Pd and Ca) during sulfur measurement as carbon monosulfide (CS) by high-resolution continuum source graphite furnace molecular absorption spectrometry. Sulfur contained in different liquid samples, such as milk, orange juice, swamp water, urine and digested samples (whole egg powder and rice flour), has been stabilized during drying and pyrolysis steps. Monitoring CS at 258.0560 nm provided the same sensitivity and thermal stability for all sulfur species tested by using 10 μL of Ca (1 g L⁻¹) and 2 μL of Pd (10 g L⁻¹), and covering the platform with Zr (400 μg). The optimum pyrolysis and vaporization temperatures were found to be 600 °C and 2300 °C, respectively. Aqueous standard solutions of ammonium sulfate, L-cysteine, and thiourea were used for calibration, in the linear range of 0.02 μg to 2 μg S (2 mg L⁻¹ to 200 mg L⁻¹ S, 10 μL injection) with a linear correlation R greater than 0.996. The LOD and LOQ were 6 ng and 20 ng S (0.6 mg L⁻¹ and 2 mg L⁻¹ S), respectively, with a precision of 0.5% to 7% RSD. In the accuracy evaluation, concordances of 93% and 100% for NIST 8415 and NIST 1568a, respectively, have been found in the comparison of the certified value and that found by the proposed method. The developed method was employed for direct S determination in different samples and also those prepared via the microwave assisted digestion procedure. No significant differences (p > 0.05) were found.