Evaluation of Some Digestion Methods for the Determination of Heavy Metals in Sediment Samples by Flame-AAS

This paper describes a number of digestion methods for the determination of Pb, Cu, Cd, Zn, Ni, Mn, Fe, Co and Cr in standard sediment samples by flame atomic absorption spectroscopy (flame-AAS). The methods involve the use of different acid mixtures, HNO3-HCl (3:1 and 1:3), HNO3-H2O2 (1:1), HNO3-H2O (1:1), and HNO3-H2SO4 (1:1) and different techniques of digestion including hotplate, microwave oven, ultrasonic bath and ultrasonic bath followed by hotplate digestion. The best digestion method involves the use of reverse aqua regia, HNO3-HCl (3:1) with 45 minutes ultrasonification at 60 °C followed by hotplate treatment for 45 minutes. This method has been successfully demonstrated for the nine heavy metals in two reference sediments with recoveries of 71-102% for SRM 2704 Buffalo River sediment and 85-105% for the AGAL-11 reference sediment from the Hawkesbury River.