Selection of chromatographic separation conditions for reliable monitoring of the transformation of AgNPs/Ag(i) species by HPLC-ICP-MS in surface water and green algae cells†

A new method based on high performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been developed for the speciation analysis of silver nanoparticles (AgNPs) and dissolved silver forms (Ag(I)) in surface water and algal cells. Different compositions of the mobile phase, including surfactants preventing agglomeration/aggregation of AgNPs, pH buffers and complexing agents for silver ions, were carefully investigated to ensure complete elution and stability of silver species during chromatographic analysis. Under the optimal separation conditions (mobile phase: 10 mM sodium dodecyl sulfate, 2 mM citrate buffer, and 2 mM tiopronin), detection limits of 2.0 ng L⁻¹ for Ag(I), 3.1 ng L⁻¹ for 10 nm AgNPs, and 2.2 ng L⁻¹ for 30 nm AgNPs were achieved. A linear relationship was found between the retention time of AgNPs and logarithm of particle diameter up to 40 nm, which can be used for the particle size determination in real samples. The HPLC-ICP-MS method has been successfully applied to study interactions of Ag(I) and citrate-stabilized AgNPs of different nominal diameters (10 nm and 30 nm) with green microalgae Acutodesmus obliquus in river water. The cell-associated fractions of silver were quite similar for all studied forms (silver biosorption was in the range of 77.2–82.7%). As a result of interaction with the biomass, biosynthesis of small nanoparticles (with a size of 6 nm) from Ag(I) ions and partial dissolution of 10 and 30 nm AgNPs were observed.