Determination of cadmium and lead in cassava employing slurry sampling and graphite furnace atomic absorption spectrometry after multivariate optimization

Abstract

A low cost and efficient method to determine Cd and Pb levels in cassava by graphite furnace atomization atomic absorption spectrometry (GF AAS) employing slurry sampling was developed. Slurries were prepared by cryogenic grinding of samples (40 mg), sieving for grain size at 50 mesh and addition of 2% v/v nitric acid and 1% v/v hydrogenous peroxide up to 2 mL of volume. The slurry was maintained homogeneous using air bubbling by an aquarium pump. Tungsten (500 μg) and titanium (500 μg) were the best permanent modifiers for Cd and Pb, respectively. The parameters of merit obtained under optimized conditions, AT (atomization temperature) = 1400 °C, PT (pyrolysis temperature) = 600 °C, pt (pyrolysis time) = 20 s and permanent W (500 μg) for Cd; AT = 1400 °C, PT = 450 °C, pt = 20 s, and Ti (500 μg) for Pb were: linear working range up to 6 and 50 μg L⁻¹ for Cd and Pb, respectively; limit of detection (0.001 and 0.02) μg g⁻¹ for Cd and Pb, respectively; and aqueous calibration, with r² > 0.99. The accuracy was evaluated by recovery tests and by analysis of certified reference material (NIST – SRM 1568a, rice flour) and was in agreement with the certified values for the two analytes: 0.021 ± 0.002 (n = 5 replicates) for Cd (certified value 0.022 ± 0.002) and <LOQ (n = 5) for Pb (certified value <0.010). The average sample concentrations (n = 3) were between <LOQ to 5.8 ng g⁻¹ and 0.08 to 3.18 μg g⁻¹ for Cd and Pb, respectively.