Thermal Lens Spectrometric Determination of Colloidal and Ionic Silver in Water

Collinear dual beam thermal lens spectrometric (TLS) detection, combined with flow injection analysis (FIA), was developed and applied to determine simultaneously concentrations of ionic and colloidal silver in the Russian drinking water supplies of the International Space Station (ISS). The newly developed method is based on on-line generation of silver colloids by sodium borohydride (NaBH₄). The generated silver nanoparticles exhibit an absorption maximum close to 400 nm, which enables their excitation with a 407 nm line of a Kr laser offering a very sensitive TLS detection scheme with impressive limits of detection (LOD) of 1.5μg · L⁻¹. Ionic and colloidal silver present initially in the sample can be discriminated by performing the measurements with and without NaBH₄.