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 dig estion of small biological samples in closed-vessel microwave systems is examined for the inductively coupled plasma atomic emission spectro scopy (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 opt imized for the successful decomposition of 50 to 90 mg of pondered bio logical samples. Microwave energy was efficiently coupled by addition of 250 mu L of distilled deionized water to the sample. A single micro wave-assisted, vapor-phase acid sample digestion was accomplished with in 30 min (including cooling time) at similar to 1200 psi pressure and 450 W microwave power in a commercial pressurized microwave decomposi tion (PMD) system. Multiple microwave-assisted, vapor-phase acid diges tions were achieved at moderately high pressure (400 to 480 psi) and 2 30 degrees C with a second closed-vessel microwave apparatus. The resu lts for 10 elements in biological standard reference materials agree w ell with the certified values.