Simultaneous determination of Pb and Cd in seafood by ICP OES with on-line pre-concentration by solid phase extraction with amberlite XAD-4 after complex formation with DDTP

ABSTRACT

An on-line method for Cd and Pb pre-concentration and simultaneous determination in acid digested seafood by inductively coupled plasma optical emission spectrometry (ICP OES) was developed. The on-line pre-concentration was based on the complex formation of the analytes with the ammonium salt of O,O-diethyldithiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a homemade column. Different conditions of the flow injection system, such as solutions flow rates, nebulizer pressure and eluent concentration were optimized. Three certified reference materials of lobster hepatopancreas, dogfish liver and fish protein, three samples of fish muscle and three samples of shrimp were digested with HNO3, H2O2 and H2SO4 in a microwave system under reflux. DDTP was added in the solutions obtained, and the mixture was injected in the FI system. Calibration curves for Cd and Pb were obtained using the standard solutions in the concentration range 0.05-0.5 µg mL-1 in the digestion medium, submitted to the same pre-concentration procedure. The quantification limits (3.3 x LOD) for 5 min of pre-concentration time were 0.005 mg kg-1 Cd2+ and 0.1 mg kg-1 Pb2+ in the sample of fish or shrimp in natura, considering 1.0 g of the sample in a final volume of 50 mL. The agreement of the obtained concentrations with the certified ones (Student t-test, 95% confidence) and the recoveries of spiked real samples, from 90 to 120%, demonstrated good accuracy. Precision was also adequate, with relative standard deviations from 2 to 13%. The method was accurate, precise and certainly could be applied to the digested samples of different natures.