Cadmium and Lead in Grey Wolf Liver Samples: Optimisation of a Microwave-Assisted Digestion Method

Abstract

A microwave-assisted digestion method for the determination of cadmium (Cd) and lead (Pb) by inductively coupled plasma mass spectrometry (ICP-MS) was optimised on certified reference material (CRM) (bovine liver, BCR-185R) and wolf liver samples. Different factors influencing digestion efficiency (temperature, time, composition of the digestion mixture, sample mass) were tested. Validation included linearity (up to 200 μg L^-1 for Cd and Pb), detection (0.003 μg L^-1 for Cd and 0.035 μg L^-1 for Pb), and quantification (0.008 μg L^-1 for Cd and 0.081 μg L^-1 for Pb) limits. Good agreement between measured and certified values was achieved in all conditions, with recoveries ranging from 94 % to 111 % for Cd and from 95 % to 105 % for Pb. The precision of the method, expressed as relative standard deviation, was up to 3 % for Cd and 8 % for Pb. The best digestion parameters (260 °C, 30 min, 1 mLHNO₃+4 mL H₂O, 0.1 g of CRM) based on accuracy and precision were applied on two wolf liver samples to evaluate the need for the pre-digestion step (freeze-drying) and appropriate mass of the sample. Freeze-drying improved precision and minimising the tissue mass to 0.1 g reduced the matrix effect. Using these optimised digestion conditions, we determined Cd and Pb in 40 wolf livers collected in Croatia, and their medians (0.055 μg g^-1 and 0.107 μg g^-1, respectively) were in the range of previously reported data for the grey wolf.