Sorption of Trace Metals on Fish Scales and Application for Lead and Cadmium Pre-concentration with Flame Atomic Absorption Determination

Ground fish scales were characterized as a solid phase extraction medium for preconcentration of parts per billion levels of transition elements prior to their flame atomic absorption spectroscopic (FAAS) determination. At the indicated optimum pH, sorption follows the order Cd2+ (pH 7.0) ≥ Pb2+ (pH 5.5) Fe3+ (pH 4.8) Cu2+ Zn2+ (pH 6.0) Ni2+ (pH 7.5) Mn2+ (pH 8.5) Cr3+ (pH 4.8). At pH 5.5, following 60-minutes of equilibration of the adsorbent with the aqueous metal ion solution sorption of Pb and Cd were 97% to 93% depending on the metal concentration. Sorption of other metal ions at pH 5.5 ranged between 80% for Cu2+ and 26% for Mn2+ but equilibration time was much longer than 60 minutes. Application of the data on Langmuir and Freundlich equations revealed that the Freundlich isotherm better suited the adsorption data. Fish scales were used for about 47 fold pre-concentration of Cd and Pb from wastewater samples, which was followed by leaching the adsorbed metals with 0.010M ethylenediamine tetra acetic acid solution and FAAS determination. The proposed method is capable of determining Pb and Cd in wastewaters with a detection limits of 1.2 μg l^-1 and 0.6μg l^-1, respectively. Compared with direct determination of Pb and Cd by graphite furnace atomic absorption spectroscopy (GFAAS), the proposed pre-concentration method resulted in comparable accuracy and a precision of less than 3.5% relative standard deviation.