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 soli d samples is very complicated. One of the approaches that have been evaluat ed in order to improve the detection limits for this element is the use of electrothermal vaporization (ETV) as an alternative means of sample introdu ction in ICP mass spectrometry. In this way, it is possible to achieve a si gnificant decrease of the oxygen-based interferences. In this work, the pos sibilities of electrothermal vaporization ICP-MS for sulfur determination a re extended one step further, as the direct determination of the analyte in two Bisphenol samples (about 0.3 and 2 mug g(-1)) is carried out. Bispheno l A is a precursor in the production of polycarbonate and epoxy resins, in which sulfur is present as an impurity. S-34 was the isotope selected for t he determination. Palladium (0.5 mug) was found to be the best chemical mod ifier and is capable of both preventing analyte losses (up to a pyrolysis t emperature of 400 degreesC) 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 o f 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 mug g(-1)) and a reduced risk of analyte losses and/or contamination. Mor eover, it presents some advantages over the dedicated sulfur analyzers that are very popular in the industry: low sample consumption (a few milligrams ), multielement possibilities and the ability to use aqueous standard solut ions for calibration. On the other hand, the overall method cannot be consi dered as very economic, but, for many laboratories that already own an ICP- MS instrument, the acquisition of an ETV device would be relatively inexpen sive.