Microwave-assisted cloud point extraction of Rh, Pd and Pt with 2-mercaptobenzothiazole as preconcentration procedure prior to ICP-MS analysis of pharmaceutical products

Abstract

New approaches for acceleration of cloud point extraction of Rh, Pd and Pt by microwave and ultrasound irradiation have been investigated. 2-Mercaptobenzothiazole and Triton X-100 were used as ligand and non-ionic surfactant, respectively. Microwave irradiation substantially increased the procedure efficiency. In contrast no significant effect was observed when a micellar solution was treated with ultrasound energy. The acceleration of complex formation reactions by reducing agents (KI and SnCl₂) has also been studied. The use of SnCl₂ was a prerequisite for quantitative extraction of Rh. Since the extraction kinetics of platinum depends on its oxidation state and presence of Pd, the addition of SnCl₂ equalized the platinum extraction behavior. For the first time the whole cloud point procedure was successively accomplished in a microwave system. 10 min of irradiation were sufficient for gravimetrical phase separation and quantitative extraction of platinum group metals. As a result the procedure time was shortened by a factor of 9 in comparison to conventional hot plate cloud point extraction. The surfactant-rich phase was analyzed after dilution with 1 M HCl by continuous nebulization to ICP-MS. Quantitative recoveries and good plasma tolerance were reported. Detection limits of 1 ng.l⁻¹ (Rh), 5 ng.l⁻¹ (Pd), and 6 ng.l⁻¹ (Pt) were achieved regarding a preconcentration factor of 8. The microwave-assisted cloud point extraction has been successfully applied for simultaneous determination of trace amounts of platinum group metals in pharmaceutical products (Tritace, Vivace, Laprilen and Enalapril).