These analytical procedures, if not differently specified, are to be applied to limpid solutions not containing oxidising or reducing agents, suspended solids, organic substances and colloids. Samples are meant to be prepared in order to fulfil these conditions, leading to a final solution of pH in the range 1 – 10, to avoid any damage to the equipment. Prepare samples, standard solutions for additions and supporting electrolytes using ultra- pure bidistilled water and clean chemicals (reagents for trace metals analysis). Always perform a blank analysis when environmental pollutants are investigated, like lead, zinc, copper, iron and chlorides.