Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles

Development of a microwave sample preparation method for the determination of arsenic in humus and moss samples by graphite furnace atomic absorption spectrometry

Two sample decomposition methods were optimized for the determination of arsenic by graphite furnace atomic absorption spectrometry (GFAAS) in moss and humus samples. In the first method, 5,0 ml of HNO$_3$ and 3,0 ml of H$_2$O$_2$ were used for the decomposition of 500 mg of sample. When humus samples were decomposed in this way a slight, undissolved residue remained. Therefore, another sample decomposition method, including hydrofluoric acid, was also tested (5,0 ml HNO$_3$; 3,0 ml H$_2$O$_2$; 0,4 ml HF; 2,5 ml H$_3$BO$_3$). Pyrolytically coated graphite tubes, equipped with integrated or L'vov platfoms, were used in the determination of arsenic by GFAAS. Palladium-magnesium nitrate was used as a matrix modifier. Several reference materials (e.g. humus, moss, lichen, sea lettuce) were analyzed