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R9 Laboratory SOP 513
ANALYSIS OF SOLIDS FOR ARSENIC, LEAD, SELENIUM AND THALLIUM BY
GRAPHITE FURNACE ATOMIC ABSORPTION SPECTROMETRY
Summary
This method provides procedures for the determination of total recoverable elements by graphite furnace atomic absorption (GFAA) in soil, sludge, sediment, oil, biological tissue and other solid matrix samples. This method is based on SW846 Method 7010. Although methods have been reported for the analysis of solids by atomic absorption spectroscopy, the technique generally is limited to metals in solution or solubilized through some form of sample processing. Soil, sludge, sediment, oil, biological tissue and other solid matrix samples must be subjected to a solubilization process before analysis. This process may vary because of the metals to be determined and the nature of the sample being analyzed. Solubilization and digestion procedures are presented in Region 9 Laboratory SOP #'s 405 and 420.
Arsenic, lead, selenium and thallium are determined by stabilized temperature platform graphite furnace atomic absorption (STPGFAA). In STPGFAA, the sample and the matrix modifier are first pipetted onto the platform or a device which provides delayed atomization. The furnace chamber is then purged with a continuous flow of high purity argon gas and the sample is dried at a relatively low temperature (about 120°C) to avoid spattering. Once dried, the sample is pretreated in a char or ashing step which is designed to minimize the interference effects caused by the sample matrix. After the char or ashing step the furnace is allowed to cool prior to atomization. The atomization cycle is characterized by rapid heating of the furnace to a temperature where the analyte is atomized from the pyrolytic graphite surface into a stopped gas flow atmosphere of high purity argon. The resulting atomic cloud absorbs the element specific atomic emission produced by a hollow cathode lamp (HCL) or an electrodeless discharge lamp (EDL). Following analysis the furnace is subjected to a clean out period of high temperature and continuous argon flow. Because the resulting absorbance usually has a nonspecific component associated with the actual analyte absorbance, an instrumental background correction device is required to subtract from the total signal the component which is nonspecific to the analyte. In the absence of interferences, the background corrected absorbance is directly related to the concentration of the analyte. Interferences relating to STPGFAA must be recognized and corrected. Suppressions or enhancements of instrument response caused by the sample matrix must be corrected by diluting the sample matrix.