Heating In a mlcrowave oven In the presence of acid mixtures dlssolves the metals from powdered coal, fly ash, 011 shales, rocks, sediments, and blological materlals. The dlssolutlon Is complete wlthln 3 min. Nearly 25 elements (AI, As, and Zn) from the dlssolved samples are determlned by Inductlvely coupled plasma emisdon spectrometry. The method has been tested oh a varlety of standard reference materlals, with reproducible and accurate results.Recently we published a multitechnique analytical scheme for the multielemental analysis of coal and fly ash samples (1). A majority of elements in that study were determined following Parr acid bomb dissolutions. This procedure needs prior ashing of the coal samples in a muffle furnace (8 h) or in a low-temperature rf asher (3 days). Subsequently, the ash is dissolved in an acid mixture in a Parr bomb in about 2 h of heating. Even though Parr bombs have been extensively used in dissolution in our laboratory and elsewhere, with prolonged usage, some of the defects apparent in them are occasional contamination of the sample solution from the metallic parts of the bomb and increasing difficulty of fitting the inner Teflon vessel into the outer metal casing as the bombs are repeatedly used. When several hundred samples a month are rountinely to be analyzed in this fashion, the cleaning and the maintenance of these bombs become quite a chore. Most other wet digestion techniques involve constant supervision and prolonged time for complete dissolution. There are also the possibilities of trace elements' loss and contamination during these steps.In the search for an alternative wet digestion technique, use of a microwave oven for rapid sample dissolution seemed to be an attractive procedure. Previous reports of analytical applications of microwave oven include those for biological and mineral-metal samples dissolution by Abu-Samra et al. (2), Barrett et al. (3), and Matthes et al. (4). Major and trace elements were determined by atomic absorption spectrometry and neutron activation analysis in these studies. We have systematically investigated the use of microwave oven dissolutions in a variety of complex matrices and very satisfactory results have been obtained for about 25 elements measured by inductively coupled plasma emission spectrometry.EXPERIMENTAL SECTION Microwave Oven. A commercial domestic microwave oven-the Sears Kenmore-was purchased in a local store. The oven has a variable timing cycle from 5 s to 60 min and a variable heating cycle based on power settings from "warm" through "high" which are equivalent to 90 through 625 W of power output. The microwave frequency is 24.5 MHz. The oven's capacity is 1.3 ft3. Earlier reports on the use of microwave ovens for the dissolution of biological materials (2,3) indicate that the acid fumes generated during the dissolution rapidly attack the electronics of the oven and damage the magnetron. The above workers used Pyrex and Plexiglas boxes inside the oven and evacuated the acid fumes with different degrees of success. It ha...

The coal sample is first ashed with high temperature ashing or with RF plasma low temperature ashing. The coal ash or fly ash can be analyzed for major ash elements by fusing with lithium tetraborate in an automatic fusion device, the Claisse Fluxer. The ash samples are also dissolved in a Parr bomb in a mixture of aqua regia and HF. Subsequently, the solutions are analyzed for eight major (AI, Ca, Fe, K, Mg, Na, Si, and Ti) and 20 trace elements (As, B, Ba, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, P, Pb, Sb, Se, Sr, U, V, and Zn) by inductively coupled plasma emission spectroscopy. Mercury in coal and fly ash is determined on a separate aliquot by the cold vapor atomic absorption technique. Fluorine and chlorine in the samples are determined by fusing with Na,CO, and Eschka mixture, respectively, and then measuring the two ions In solution with specific ion electrodes. Oxygen in the samples can be determined rapidly and nondestructively by 14-MeV neutron activation analysis. These methods have been tested by analyzing several NBS coal and fly ash standards with good accuracy and reproducibility.Oil and gas a t present supply three-fourths of the energy used in the United States. In spite of the increasing conservation measures taken, our import of these materials is steadily on the rise. However, the supply of these hydrocarbon fuels worldwide is expected to decline in the foreseeable future.T h e only practical alternative energy supplies a t present are nuclear energy and coal.T h e world reserves of coal far exceed those of any other fossil fuel and are sufficient to support a massive increase in consumption well into the future. It is estimated that the United States has 1.7 trillion tons of coal ( I ) . Despite these massive reserves, however, the amount of coal used in this country has remained almost constant a t about 600 million tons per year for the past few years ( 2 ) . One of the chief reasons for this lack of coal utilization is the environmental concern as to how much increase in atmospheric pollution will take place by burning increased amounts of coal.Coal is a fairly "dirty" fuel and contains large amounts of many inorganic elements. At the same time, there are wide variations in the trace elements content of coal seams even within a single mine. Hence, it is important to have reliable analytical methods which can monitor the inorganic constituents a t various stages of coal production and utilization. Since as many elements as possible need to be monitored in the coal products, it is desirable to have multielement rather than single element techniques.The need for the standardization of the analytical methodology and availability of analytical standards was illustrated by the U S . Environmental Protection Agency's round robin analysis of four fuel matrices for 28 elements in nine laboratories (3). Same samples of coal, fly ash, fuel oil, and gasoline were analyzed for 28 elements in nine laboratories by a variety of analytical techniques -neutron activation analysis, atomic absorption spectrophoto...

We wish to thank William Norris of Wright State University for the sediment sample from Grand Lake St. Mary's. Appreciation is also due Tom Bellar, of this laboratory, who extracted the sediment sample, and Ron Webb, of the Southeast Environmental Research Laboratory, who provided the samples of characterized PCB isomers.

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