A SIMPLE METHOD FOR LEAD AND CADMIUM DETERMINATION IN FISH USING ALKALINE SOLUBILIZATION AND GFAAS

Lead (Pb) and cadmium (Cd) are among the seven top substances on the priority list of hazardous substances of the American Agency for Toxic Substances and Disease Registry (ATSDR).1 These metals are considered to be carcinogenic to humans by the International Agency for Research on Cancer (IARC), even at low concentrations.2,3 Due to their high toxicity, these metals are among the controlled substances in fish muscle, with a maximum permissible limit of 0.3 mg kg-1 for Pb and 0.05 mg kg-1 for Cd. Analytical methods that can provide accurate and precise measurements with low detection limits and simplicity are necessary for food quality control.4 In that sense, this work aimed to develop and validate a simple and fast method for determination of Pb and Cd in fish using alkaline solubilization with tetramethylammonium hydroxide (TMAH) and quantification by graphite furnace atomic absorption spectrometry (GFAAS). To optimize the method, it was evaluated the sample mass, TMAH volume, temperature and time of heating, in addition the temperature program of GFAAS. Multivariate optimization was used to establish the important variables as well as optimal conditions for analysis. The optimized method is described as follows: fish muscle samples weighing 750 mg were placed in 50 mL conical tubes, to which 1.0 mL of 25% (v/v) TMAH solution was added, followed by incubation at 70 °C for 30 min. Then the volume was completed to 10 mL with a solution containing 1% (v/v) H3PO4. This solution was directly analyzed by GFAAS. The method was validated following the procedures and acceptability criteria of the National Agricultural Laboratories (LANAGRO) of the Brazilian Ministry of Agriculture (MAPA). No matrix effects were observed and external calibration curve was performed. The limits of detection and quantification were 7.8 and 26.0 μg kg-1 for Pb and 1.2 and 4.1 μg kg-1 for Cd, respectively. The accuracy and trueness of the method were evaluated using a certified reference material (CRM) of fish muscle, with recovery between 91.4 – 114.4% (n=9) and relative standard deviations no more than 9.8%. The method was successfully used to analyze fish samples collected by the Minas Gerais state Sanitary Surveillance Agency. The method is simple and fast and the evaluation of all analytical parameters demonstrates that the proposed method provides satisfactory results.