9. Determine desorption efficiency (DE) at least once for each batch of charcoal used for sampling in the calibration range (step 8).
a. Prepare three tubes at each of five levels plus three media blanks.
b. Inject a known amount of DE stock solution (5 to 25 μL) directly onto front sorbent section of each charcoal tube with a microliter syringe.
c. Allow the tubes to air equilibrate for several minutes, then cap the ends of each tube and allow to stand overnight.
d. Desorb (steps 5 through 7) and analyze together with standards and blanks (steps 11 and 12).
e. Prepare a graph of DE vs. μg analyte recovered.
10. Analyze a minimum of three quality control blind spikes and three analyst spikes to insure that the calibra tion graph and DE graph are in control.