Speciation analysis of antimony by high-performance liquid chromatography inductively coupled plasma mass spectrometry using ultrasonic nebulization

Abstract

The two inorganic Sb species Sb(III) and Sb(V) as well as trimethlyantimony dichloride (TMSbCl 2) were separated by anion exchange chromatography. HPLC eluents were directly aspirated into the plasma of an ICP-MS using ultrasonic nebulization (USN) with membrane desolvation. Leaching of Sb from glass bottles, especially pronounced under alkaline conditions, distinctly increased background 121Sb signals. The use of conventional HPLC syringes made of glass resulted in non reproducible blank signals for Sb(V). To overcome these problems, polyethylene bottles for the storage of mobile phases and plastic syringes for the injection of Sb compounds onto the analytical columns were employed. The analysis of Sb(III) standard solutions in the sub μg l −1 range prepared by dilution of stock standard solutions with high-purity water revealed that Sb(III) is easily oxidized to Sb(V) within a few hours. Deoxygenating the water for dilution of standards by flashing working standard solution with helium or using 1.25 mM EDTA — which served as mobile phase for the chromatographic separation — for the dilution of standards, no oxidation of Sb(III) was observed, at least for 8 h. USN parameters, such as the temperature of the heating area and of the desolvation area as well as the sweep gas flow rate were systematically optimized. Decreasing the USN heating temperature from the conventional settings of 140–80°C enhanced signal intensities by ∼25% and caused no condensation of the aspirated mobile phase. After optimization detection limits for all three Sb species in the low ng l −1 range could be established, namely 14 ng l −1 for Sb(III), 12 ng l −1 for Sb(V) and 9 ng l −1 for TMSbCl 2.