An international interlaboratory study for the production of a sewage sludge certified reference material for routine use in inorganic quality control

Two existing interlaboratory schemes are used to certify a sewage sludge reference material. Data from the analysis (As, Cd, Cr, Cu, Pb, Hg, Ni and Zn) of the material using routine procedures, US EPA and Netherlands NEN, plus INAA and IDMS and an interlaboratory comparison in Eastern Europe have been examined. The Dutch results show significantly lower analytical results for As for the graphite furnace technique compared to HG-AAS, probably due to matrix-effects. The differences between the Dutch and USA results for Cr and Ni suggest that the USEPA 3050A digestion method for dissolution of the metals is less aggressive for this material compared to aqua regia destruction. For international comparability of analytical data it is essential to harmonize method dependent dissolution/extraction techniques. The preparation of reference materials which mimic real samples and certification by ILS result in useful materials for quality control.