QUANTITATIVE-ANALYSIS OF ORGANIC WASTES - EFFECTS OF SAMPLE PREPARATION IN THE DETERMINATION OF METALS

One of the most important analytical problems is the sample preparatio n to measure the total concentration of elements. Ashing procedure and microwave preparation are two important methods used. Ashing procedur e is based in the mineralization of the sample in a furnace for 6 to 8 hours at 400 to 500 degrees C followed by acid dissolution. Microwave digestion is based in an acid attack of the sample favoured by electr othermal radiation for some minutes. Organic residues are often used a s soil amendments in agriculture. Some of them like sewage sludge and urban residues have heavy metals in their composition. It is important to measure them in order to establish their adequate use and minimize the potential environmental pollution. In this work, cadmium (Cd), co balt (Co), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), le ad (Pb), and zinc (Zn) were analyzed in six residues from agriculture (almonds residue), cities (urban refuses from Madrid and Gandia-Valenc ia), and three sewage sludge from a tourist town (Benidorm), an indust rial town (Onteniente) and Madrid. Two certified reference material we re also analyzed (sewage sludges: BCR-144 and BCR-146). These samples were mineralized by both procedures commented and total concentration of metals were determined using inductively coupled plasma emission sp ectrometry (ICP-AES). Results showed relatives differences depending o n the metal and the kind of waste material mineralized. Lead was not a ffected by the preparation method. Lower values of Cd were usually fou nd in the microwave mineralization than ashing procedure; however, Zn and Cr seemed to be detected in major quantities in the microwave solu tion. Poor differences were observed for the rest of the elements anal yzed.