Microwave-assisted vapor-phase nitric acid digestion of small biological samples for inductively coupled plasma spectrometry

The applicability of micro,val e-assisted, vapor-phase nitric acid digestion of small biological samples in closed-vessel microwave systems is examined for the inductively coupled plasma atomic emission spectroscopy (ICP-AES) determination of 10 elements (Al, As, Ca, Cu, Cd, Fe, Mn, Mo, Ph, and Zn). A 1.8 mL quartz sample container geometry was optimized for the successful decomposition of 50 to 90 mg of pondered biological samples. Microwave energy was efficiently coupled by addition of 250 mu L of distilled deionized water to the sample. A single microwave-assisted, vapor-phase acid sample digestion was accomplished within 30 min (including cooling time) at similar to 1200 psi pressure and 450 W microwave power in a commercial pressurized microwave decomposition (PMD) system. Multiple microwave-assisted, vapor-phase acid digestions were achieved at moderately high pressure (400 to 480 psi) and 230 degrees C with a second closed-vessel microwave apparatus. The results for 10 elements in biological standard reference materials agree well with the certified values.