A number of different digestion methods, including aqua regia extraction following two ISO guides were used in an inter-laboratory comparison study. The results obtained showed comparable values for the total and aqua regia extractable content of As, Cu, Fe, Hg, Pb and Zn, while Cd, Co and Cr results were about 10% lower when aqua regia was employed. This small difference was covered by the between-laboratory relative standard deviation of the measurements; therefore in this study no difference in the extraction of the elements by the employed methods was found. The high organic matter content, together with low SiO2 and refractory aluminium and iron oxide amount as well as the small particle size of the sewage sludge material was reputed to have an effect on the extracting capacity of a weaker solvent such as aqua regia, bringing its results close to the total content ones.
A reference material of a PM2.5-like atmospheric dust material has been prepared using a newly developed method. It is intended to certify values for the mass fraction of SO4 2−, NO3 −, Cl− (anions) and Na+, K+, NH4 +, Ca2+, Mg2+ (cations) in this material. A successful route for the preparation of the candidate reference material is described alongside with two alternative approaches that were abandoned. First, a PM10-like suspension was allowed to stand for 72 h. Next, 90% of the volume was siphoned off. The suspension was spiked with appropriate levels of the desired ions just prior to drop-wise shock-freezing in liquid nitrogen. Finally, freeze drying of the resulting ice kernels took place. In using this approach, it was possible to produce about 500 g of PM2.5-like material with appropriate characteristics. Fine dust in 150-mg portions was filled into vials under an inert atmosphere. The final candidate material approaches the EN12341 standard of a PM2.5-material containing the ions mentioned in Directive 2008/50/EC of the European Union. The material should be analysed using the CEN/TR 16269:2011 method for anions and cations in PM2.5 collected on filters. The method described here is a relatively rapid means to obtain large quantities of PM2.5. With access to smaller freeze dryers, still 5 to 10 g per freeze-drying cycle can be obtained. Access to such quantities of PM2.5-like material could potentially be used for different kinds of experiments when performing research in this field. Graphical abstractThe novelty of the method lies in transformation of a suspension with fine particulate matter to a homogeneous and stable powder with characteristics similar to air-sampled PM2,5. The high material yield in a relatively short time is a distinct advantage in comparison with collection of air-sampled PM2,5
A certified reference material (CRM) of brown algae is being developed at the Institute for Reference Materials and Measurements (IRMM), European Commission, Joint Research Centre, in order to supply academic and industrial analysts with a new tool useful in the environmental analysis of trace metals.Sixty kg of raw brown algae (species Fucus vesiculosus) was collected from two different sites in Galway (Ireland) and processed according to ISO 34 and ISO 35. A large amount of milled and sieved (at <125 μm) algae material was bottled and subjected to detailed homogeneity and stability tests with regard to the parameters to be certified.The between bottle homogeneity of the total element content of As, Cd, Cu, Hg, Pb, Se and Zn was assessed via a dedicated test, which confirmed the suitable homogeneity of the candidate CRM. The short term stability of the material when stored at high temperature (60°C) for up to 4 weeks was also considered, confirming no degradation under the conditions applied.Milled and sieved algae was also checked for water content by using KarlFischer titration and several oven temperatures (from 85°C to 110°C) in order to establish the most reliable water determination method for the material.Along with these studies, a long term stability isochronous study and the characterisation of the total element content for the above-mentioned metals by using an inter-laboratory comparison approach are in progress, so as to finalise production and release onto the market the brown algae CRM for trace metal analysis.
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