**2.1.4 Sample preparation procedures**

Sea, river and industrial water samples collected in Nalgene plastics were acidified by adding 1 mL of hydrochloric acid (0.1 M) per 100 mL of sample solution behind filtration over 0.45 m Millipore Filter (Millford, MA). After filtration, 20 L of water samples were injected directly into the FIA system for the determination of iron (II). Total iron was determined by reducing of all forms of iron to iron (II) in the procedure described (van Staden J.F. and Kluever L.G. 1998; Asan A., et al. 2003).

A 0.10 g sample of the certified metal alloy (Zn/Al/Cu 43XZ3F) was dissolved in 12 mL of concentrated HCl+HNO3 (3:1 v/v) in 100 mL beaker. The mixture was heated on a hot plate nearly to dryness; 5 mL HNO3 was added to complete dissolution and diluted to 100 mL with deionized water. The solution was filtered and transferred quantitatively to 1000 mL volumetric flask and made up to volume with deionized water. 9 mL of this solution was treated with 1 mL of sodium azide (2.5 % w/v) for iron (III) reduction. After the reduction step, 20 L of this solution was used for the determination of total iron (van Staden J.F. and Kluever L.G. 1998).

Metal ore samples (0.10 g) were powdered ( 500 mesh) and prepared as in the procedure described above. All analyses were performed with the least possible delay.
