National Institute for Occupational Safety and Health

“ Place a Hopcalite tube in the air intake to eliminate any mercury that may be present. Adjust the peristaltic pump to a flow that will create a steady stream of bubbles in the BOD bottle, but not so great that solution droplets enter the tubing to the quartz cell. If water vapor condenses in the quartz cell, heat the cell slightly above room temperature by wrapping it with a heating coil and attaching a variable transformer. The bubbler consists of a glass tube with a bulb at the bottom, slightly above the bottom of the BOD bottle. ”

“ A second tube is provided to allow the exit of the vapor. The open end of the second tube is well above the surface of the liquid in the bottle. The two tubes are fixed into a stoppering device (preferably ground glass) which fits into the top of the bottle. ”

“ Include a minimum of three unopened sampling tubes from the same lot as the samples for use as media blanks. Cap sampler and pack securely for shipment.
SAMPLE PREPARATION: 5. 6.
7. 8. 9.
Place the Hopcalite sorbent and the front glass wool plug from each sampler in separate 50-mL volumetric flasks. Add 2.5 mL conc. HNO 3 followed by 2.5 mL conc. HCl. NOTE: The mercury must be in the oxidized state to avoid loss. For this reason, the nitric acid must be added first. Allow the sample to stand for 1 h or until the black Hopcalite sorbent is dissolved. ”