Microwave heated vapor-phase digestion method for biological sample materials

A microwave heated, vapor-phase nitric acid-hydrogen peroxide digestion met hod for pulverized, biological sample materials was developed. Sample masse s up to 200 mg were digested using calibrated quartz inserts inside first g eneration type, low-pressure, Teflon-PFA microwave vessels. In the first st ep, samples were digested in the vapor-phase for 80 min using a progressive heating pattern. Three mL of 70% nitric acid and 0.5 mL of 30% hydrogen pe roxide were used as digestion reagents. In the second step, the small resid ue left after first step digestion was dissolved in 1.4% nitric acid or add itionally with 0.5% hydrofluoric acid by heating for 15 min. The digestion method was optimized using pike (Esox lucius) muscle as a test material. Th e method was further optimized using three certified reference materials. C a, Cu, Fe, Mg and Zn were determined from NIST-SRM 1577a bovine liver by IC P-AES. Cr and Ni were determined from NIST-SRM 8433 corn bran and NRCC DOLT -2 dogfish liver by GFAAS. For all elements the values obtained were close or within certified limits. Spike recoveries were between 96 to 107%. Diges tion efficiency ranged from 91 to 99%.