Optimization of interface materials for the determination of traces of bromine and selenium by low-pressure helium ICP-MS

Abstract

Although ICP-MS offers a powerful multielement analytical method, the mass spectral interference due to argon often becomes a serious problem. For example, 40Ar16O+, 40Ar35Cl + and 40Ar2+ interfere with the determination of 56Fe+, 75As+ and 80Se+, respectively. Therefore, we replaced argon by helium to develop an interference-free ICP-MS, and successfully detected iron and arsenic in aqueous solutions. Some weak background peaks, however, were still generated at m/z 79-82 and disturbed the determination of traces of bromine (79Br+) and selenium (80Se +). In the present work, it was found that these peaks originated from the copper interface by a secondary discharge. They were assigned to 63Cu16O+, 63Cu16OH +, 65Cu16O+ and 65Cu 16OH+. The nickel interface caused more serious background at m/z 50-100. On the other hand, no spectral interference was observed over a wide m/z range when the interface was constructed from aluminum. The optimized helium ICP-MS was used for the determination of traces of bromine and selenium in water. A 5 μl volume of a sample was placed and heated electrothermally on a tungsten filament. The resulting vapor was introduced into the helium plasma for a mass spectrometric analysis. The relative standard deviation of the signals (10 ng ml-1, n = 10) was approximately 10%. The detection limits based on 3σ were 0.2 ng ml-1 for Br and 0.09 ng ml -1 for Se, which were lower compared with the conventional argon ICP-MS (Br 20 ng ml-1, Se 0.25 ng ml-1).