Microwave digestion
The dissolved dye, incense stick, and hand wiping samples were digested by microwave digestion. The instructions of microwave using were same in every sample but the weight, chemical reagents, and condition of samples were different. Table 3.2 shown the condition of microwave digestion for dissolved dye, incense stick, and gauze wiping samples. Before using microwave digestion, the solid samples should be grinded to digest heavy metal out easily. For dissolved dye, using pipet sucked 250 μl of the samples. For incense stick and hand wiping samples, weighed grinded incense stick 0.5g and hand wiping samples 0.3g, respectively into polyethylene vessels then the polyethylene vessels were composed into HTC safety shield. The chemical reagents of each sample that shown in Table 3.2 were added into the polyethylene vessels then closed the vessel by using the torque wrench to tight them. The segments were inserted into microwave cavity and connect the temperature sensor then ran the microwave program depending on types of sample that shown in Table 3.2. When finish all of steps in microwave digestion, cooling the rotor by air or water until the solutions in the polyethylene vessel down to room temperature. After that, the vessels were opened and filtrated the solutions by Whatman No. 41 filter paper on glassed cone with 25 ml volumetric flask. After the solutions were adjusted, contained the solution into polyethylene bottle for quantitation the heavy metal concentrations in the next step.