Direct determination of sulfur in solid samples by means of high-resolution continuum source graphite furnace molecular absorption spectrometry using palladium nanoparticles as chemical modifier

Abstract

This work investigates the potential benefits of using Pd nanoparticles, in combination with Ru as permanent modifier, for sulfur monitoring as CS by means of high-resolution continuum source graphite furnace molecular absorption spectrometry. Upon heating, these small (approx. 20 nm diameter) Pd nanoparticles are evenly distributed over the platform surface, offering a larger surface for interaction with the analyte during the drying and pyrolysis steps. In this way, a more efficient stabilization of sulfur species can be achieved. Furthermore, a similar analytical response is obtained regardless of the chemical form in which sulfur species are originally found, thus making it easier to develop quantitative analytical methods for this analyte. When using these modifiers, and under optimized working conditions, it is possible to use this technique for direct analysis of different types of solid samples (biological, petroleum coke, polyethylene and steel CRMs), thus circumventing the traditional drawbacks associated with sample digestion when sulfur determination is aimed at. Accurate results are obtained using only the central CS line found at 257.958 nm, with precision values in the 5–10% RSD range (14 ng characteristic mass; 9 ng limit of detection). Moreover, the combined use of the main six CS lines available in the spectral area simultaneously monitored by the detector permits to further improve precision to 3–5% RSD, while decreasing the limit of detection down to 3 ng (the characteristic mass is also 3 ng), which represents a relative limit of detection of approx. 1 μg g⁻¹, as calculated for the sample with the lowest sulfur content. In all cases, straightforward calibration with aqueous standards was proved to be feasible, and the sample throughput is of 3–4 samples per hour (5 replicates per sample).