LEAD by Flame AAS: Method 7082, Issue 2, dated 15 August 1994 - Page 5 of 7 Mark Millson, NIOSH/DPSE and R. DeLon Hull, Ph.D., NIOSH/DBBS; S341 originally validated under NIOSH Contract CDC-94-74-45; additional studies under NIOSH Contract 210-79-0058. James B. Perkins, David L. Wheeler, and Keith Nicholson, Ph.D., DataChem Laboratories, Salt Lake City, UT, prepared the microwave digestion procedure in the Appendix.
APPENDIX - MICROWAVE DIGESTION FOR LEAD IN PAINT CHIPS (AND OTHER MATRICES) This procedure is an alternative to the procedure presented in the Sample Preparation section of this method. It provides a rapid, complete acid digestion prior to analysis by flame atomic absorption (FAA), heated graphite furnace atomic absorption(HGFAA), and inductively coupled plasma spectroscopy (ICP) [10]. Apparatus and Material[11-16] 1. Microwave apparatus requirements a. The microwave unit provides programmable power with a minimum of 574 W and can be programmed to within ± 10 W of the required power. b. The microwave unit cavity is corrosion resistant as well as ventilated. All electronics are protected against corrosion for safe operation. c. The system requires Teflon PFA digestion vessels (120-mL capacity) capable of withstanding pressures up to 7.5 ± 0.7 atm (110 ± 10 psi) and capable of controlled pressure relief at pressures exceeding 7.5 ± 0.7 atm (110 ± 10 psi). d. A rotating turntable is employed to ensure homogeneous distribution of microwave radiation within the unit. The speed of the turntable should be a minimum of 3 rpm. e. A safety concern relates to the useof sealed containers without pressure relief valves in the unit. Temperature is the important variable controlling the reaction. Pressure is needed to attain elevated temperatures but must be safely contained [12]. f. Polymeric volumetric ware in plastic (Teflon or polyethylene), 50- or 100-mL capacity. g. Disposable polypropylene filter funnel. h. Analytical balance, 300-g capacity, and minimum ± 0.001 g. Reagents 1. Nitric acid, concentrated, spectroscopy grade. 2. Reagent Water. Reagent water shall be interference free. All references to water in the method refer to reagent water that meets the ASTM Type 2 standard. Procedure 1. Calibration of Microwave Equipment Calibrate microwave equipment in accordance with manufacturer's instructions. If calibration instructions are not available, see EPA Method 3051 [11]. 2. All digestion vessels and volumetric ware must be carefully acid washed and rinsed with reagent water. All digestion vessels should be cleaned by leaching with hot (1:1) nitric acid for a minimum of fifteen minutes, rinsed with reagent water, and dried in a clean environment. 3. Sample Digestion a. Tare the Teflon PFA digestion vessel. b. Weigh out 0.1 g paint chip sample to the nearest 0.001 g into the tared Teflon PFA sample vessel. 2 With large paint chip samples, measure out a 2 cm piece, weigh to the nearest 0.001 g, and quantitatively transfer it to the vessel. c. Add 5.0 ± 0.1 mL concentrated nitric acid to the sample vessel in a fume hood. If a vigorous reaction occurs, allow the reaction to stop before capping the vessel. Cap the vessel and torque the cap to 12 ft-lb (16 N-m) according to the manufacturer's directions. The sample vessel may be connected to an overflow vessel using Teflon PFA connecting tubes. Place the vessels in the microwave carrousel. Connect the overflow vessels to the center well of the unit. d. Place the vessels evenly distributed in the turntable of the microwave unit using groups of two, six, NIOSH Manual of Analytical Methods (NMAM), Fourth Edition
