Microwave-enhanced analytical chemistry for leaching, total processing, and clean chemistry in inorganic analysis

Microwave heating continues to revolutionize sample preparation procedures. However, while the number of procedures using microwave heating have continued to grow, the number of techniques developed with attention to sound chemistry and method control have not. This work describes the use of microwave energy with an optimized leaching chemistry to enhance the capabilities of standard inorganic extraction methods. The chemistry of extraction methods was optimized to make them more applicable for a wide range of analytes. Specific recovery inefficiencies were addressed by including HCl as a complexing agent. In addition to providing an expanded list of validated analytes, the development of EPA Method 3051A, for solid samples, and Method 3015A, for aqueous samples, provided a level of control and method transfer that is not possible using conventional heating.; The fundamental relationships involved in microwave heating of aqueous samples were explored. The relationships among sample mass, absorption of microwave energy, and temperature were studied. Significant advances in post-dissolution processing were made by showing that the temperature actually decreases during evaporation using microwave energy. The microwave-assisted evaporation technique demonstrated excellent recoveries of analytes that are documented to be volatile using traditional evaporation techniques, including As, Hg, Sb, and Sn from HCl and HF matrices. The novel technique also showed effectiveness in dissolution and preconcentration procedures for solid materials.; A wide range of applications using the interaction of microwave energy with small samples were developed and evaluated. Microwave-assisted evaporation was used to quantify the impurities in sub-boiled acid. The technique demonstrated better recovery than evaporation techniques using the transfer of thermal energy to the solution. Novel apparatus were developed to use microwave energy to prepare dried spots for thin film Micro-X-ray fluorescence analysis.; A fundamental relationship between sample mass, sample dimensions, and microwave heating was established. The importance of sample geometry in relation to the degree of microwave heating was shown. Because of the manner in which microwave energy interacts with small samples, the geometry and dimensions of the sample become important factors in determining the degree of heating. This work develops both fundamental relationships and applications of microwave energy in analytical chemistry.