The digested sample was transferred into a volumetric flask, the reaction vessels were washed out with de-ionized water and the flask volume made up to a final volume of 25 mL. 100 μL of Yttrium standard solution (Merck) of 10 mg/mL was added as internal standard to 1 mL subsample of the digested samples and mixed. After that, 20 µL of the digested tissue sample was deposited on a silicon quartz glass holder