Behavior and Determination of Titanium Dioxide Nanoparticles in Nitric Acid and River Water by ICP Spectrometry

Abstract

ICP spectrometry (ICPMS, ICPOES) are classical techniques for the determination of solubilized or suspended elements. Unfortunately, their relevance for nanoparticles at low concentration (below 10 ppm) is rarely called into question, even if literature reports are not always coherent. This work is a systematic study based on the measurement of TiO2 nanoparticle suspensions, as a model of quasi-insoluble material, by plasma spectrometry. It studies both sample treatment and measurement in the 10 ppb to 30 ppm concentration range. Realized on a set of four engineered nanoparticles suspensions at low concentration, it shows the existence of three different regimes of stability that affect concentration measurement. Above a C(S) stability concentration value, suspensions are stable in time; below a low-concentration C(E) value, the signal loss is at a maximum, and a final partition is reached between the container walls and the suspension. Between these two regimes, the suspension aging varies with concentration. C(E) and C(S) depend on nanoparticle characteristics and the suspension medium, whereas the evolution kinetic is volume-dependent. Because TiO2 nanoparticles are present in the environment at concentrationd below C(S), it is then necessary to find a way to rehomogenize the suspension between sampling and analyzing. Soft sonication, minimizing the sample temperature, and trapping of free radicals is proposed and evaluated. Homogenization is traced by the addition of an internal standard before storage. The procedure is applied to a real sample, Seine River water. The amount of total titanium found, 48.7 ppb, is in good agreement with the result of the reference method.