National Institute for Occupational Safety and Health

“ If the concentrations found immediately after transfer are equal to those prior to transfer, the sampling train is not altering the EtO concentration (i.e., is inert) . If the concentrations do not change over time, the bags are inert. (2) Consider any residual analyte which may remain in a bag after use, since practicality dictates reuse of bags. One or two purges with clean air are usually sufficient to remove residual EtO unless the concentration of the previous sample was extremely high. Analyze a sample of "clean" air taken from the bag during its final purge. ”

“ This creates a standard of known concentration in ppm (μL EtO/L air) . (1) Evacuate a 5- to 10-L bag completely by drawing the air out with a large (1- to 2-L) syringe. (2) Draw clean air (or oxygen or nitrogen) from a supply cylinder into the syringe for measured transfer into the bag. Alternately, if a clean air supply is not available, draw room air through charcoal sorbent into the syringe. Repeat until the bag contains 5 L of air. (3) Add a known amount of pure EtO or standard EtO mixture to the bag by means of gas-tight syringe. ”

“ Results will vary from instrument to instrument, and from time to time on the same instrument. c. Plot nL EtO vs. peak height or area. This plot should be a straight line. d. Periodically throughout the day, check calibration by repeating some of these injections of standards. Ideally, each sample would be bracketed, before and after, with injections of standards, although this is seldom practical. 3. Check the sampling equipment to prevent contamination. a. Use different syringes for sampling and for standard preparation. Identify each syringe with a unique number. ”