Depending on the type of material, samples were digested by using multiple mixtures of acids. PCB fractions were digested in 1:3 mixture of HNO3:HCl (aqua regia) (1 g of PCB to 20 mL of aqua regia solution), PH in 1:1 combination of H2SO4:HNO3 and a 1:5 mixture of HNO3:HCl was used for digesting LCD fractions, following the procedures recommended in the IEC 62321 RoHS standard, the US EPA 3052 and 3056 methods.