The techniques which are typically used to prepare RCRA wastes for analysis for metals and other elements are generally relatively time consuming, requiring several hours to several days to complete. They also often involve the use of acid digestions and thermal decomposition steps which may result in analyte losses, incomplete recoveries, or sample contamination. These limitations are well known to the analytical community and to the end users of these data in EPA, States, and industry. The resulting inefficiency of these techniques reduces laboratory sample throughput, drives up the cost of analytical testing, and impedes decision making. Given these concerns, the OSW Methods Section is interested in developing cost effective sample preparation techniques for metals and other elements in environmental and process waste samples. Once developed, these techniques can then be written as methods for inclusion in Test Methods for Evaluation of Solid Waste SW-846 and made available to the user community. This paper reports on the evaluation of a microwave assisted sample preparation method for determining elements in solid waste. The Method was evaluated for microwave digestion of sediments, sludges, soils, and oils.
The reliability of quantitative impurity analysis of solids by spark-source mass spectrometry has been improved as a result of recent investigations. In the past, the technique has been highly successful for quantitative estimation of extremely low impurity levels and for direct comparison of impurity levels in two similar materials. However, improvements in reproducibility and the establishment of reliable relative-sensitivity factors were required for accurate determination of absolute concentrations. It has now been shown that the ion-accelerating voltage and the level of rf spark excitation can have marked effects on relative-sensitivity factors. It is, therefore, extremely important to maintain these parameters constant. The influence of sample inhomogeneity on reproducibility has also been investigated, and here the very low sample consumption of the rf spark can be a disadvantage. The alternative method of excitation by low-voltage dc arc can be less affected by inhomogeneity because a larger amount of sample is involved in an analysis. Following the improvements in reliability of relative-sensitivity measurements, more systematic determinations of these factors have been carried out. It is shown that, when these correction factors are applied, quantitative accuracy of the order of 10% is achieved.
The following are summaries of two papers presented at a Joint Meeting of the Midlands Section with the Birmingham and Midlands Section of the Royal Institute of Chemistry, held on December 7th, 1967, and reported in the January issue of Proceedings (p. 2). Recent Developments in the Field of Solid-source Mass Spectrograpliy withSpecial Reference to Powder Analysis BY P. F. S. JACKSON SPARK-SOURCE mass spectrography is a comprehensive and extremely sensitive method of analysis that is finding increasing use in trace-element analysis. Work carried out with the M.S.7 mass spectrograph, which is manufactured by Associated Electrical Industries Limited, is described, in which it is shown that the range of the instrument can be extended to include concentrations much greater than those normally defined as trace. A radio-frequency spark is used to generate a positive-ion beam from the sample, which enables a wider range of materials to be examined than at first considered possible. The instrument has been used (British Titan Products Company Limited, Billinghanz, Co. Durham)
The use of microwave energy to facilitate sample decomposition prior to elemental analysis is now receiving considerable attention. Both wet and dry digestions are achievable. When microwave energy is used in combination with acid mixtures in closed vessels, the combined pressure and rapid heating can reduce digestion times to a few minutes from hours or days that may be required for open beaker digestions. This savings in time and labor is significant and has prompted the Office of Solid Waste to evaluate this technology as a preparation tool for solid wastes. Of particular interest are used oils and other fuels slated for incineration, incinerator ash, and particulates from these processes. This study reports on the evaluation of a commercially available microwave oven sample preparation system for this application. The effect of sample preparation conditions, including the acid matrix, heating time, and pressure, were evaluated for fifteen toxic or hazardous elements in particulates, ashes oils, and oil fuels. Analyses were carried out by inductively coupled plasma emission spectroscopy.
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