Direct determination of sulfur in Bisphenol A at ultratrace levels by means of solid sampling-electrothermal vaporization-ICP-MS

It is known that the accurate determination of ppm levels of sulfur in solid samples is very complicated. One of the approaches that have been evaluated in order to improve the detection limits for this element is the use of electrothermal vaporization (ETV) as an alternative means of sample introduction in ICP mass spectrometry. In this way, it is possible to achieve a significant decrease of the oxygen-based interferences. In this work, the possibilities of electrothermal vaporization ICP-MS for sulfur determination are extended one step further, as the direct determination of the analyte in two Bisphenol samples (about 0.3 and 2 µg g−1) is carried out. Bisphenol A is a precursor in the production of polycarbonate and epoxy resins, in which sulfur is present as an impurity. 34S was the isotope selected for the determination. Palladium (0.5 µg) was found to be the best chemical modifier and is capable of both preventing analyte losses (up to a pyrolysis temperature of 400°C) and improving the sensitivity. Some evidence as to the way in which it may act is also presented. Nitric acid was added as well in order to favour an efficient matrix removal prior to the release of the analyte. The resulting solid sampling-electrothermal vaporization-ICP-MS method combines very interesting features for this particular element: a high sample throughput (20–25 min per sample), a low limit of detection (4 ng g−1) and a reduced risk of analyte losses and/or contamination. Moreover, it presents some advantages over the dedicated sulfur analyzers that are very popular in the industry: low sample consumption (a few milligrams), multi-element possibilities and the ability to use aqueous standard solutions for calibration. On the other hand, the overall method cannot be considered as very economic, but, for many laboratories that already own an ICP-MS instrument, the acquisition of an ETV device would be relatively inexpensive.