Determination of uranium in aqueous solutions by the time-of-flight mass-spectrometry with a pulsed glow discharge after its accumulation on the oxidized carbon nanotubes

The pollution of the environment with uranium dictates the need to control the concentration of this element in natural waters to the permissible limits for the stability of the ecosystems and public health. In 2011, WHO set maximum permissible concentration of uranium in water to 0.03 ppm due to the strong toxicity and radioactivity of uranium in water. Therefore, the continuous monitoring of uranium content is an important task for the safety and health of the citizens. To determine the low uranium content in natural waters, the conservation of the studied solutions is necessary. However, this method of storage and transportation is not always simple. In the current paper, as a convenient method of concentrating uranium, preserving the sample and transporting it, we used the method of sorbing uranium on sorbents. Single-layer carbon nanotubes were used as sorbents. Their surfaces were modified using wet chemical oxidation and synthesis with Aerosil A-380 silica. Two schemes were considered for concentrating the uranium on the surface of the sorbent: individual carbon nanotubes and nanotubes modified with silica. The direct analysis was used to determine the content of uranium in the sorbent, namely, time-of-flight mass spectrometry with the pulsed glow discharge (GD-MS). The most effective approach for the determination of uranium in water was the sorption of uranium on the tablet consisting of oxidized nanotubes modified with silica. The limit of detection in this case was 0.2 ppb.