NITROUS OXIDE: METHOD 6600, Issue 2, dated 15 August 1994 - Page 3 of 3 INSTRUMENT PREPARATION AND CALIBRATION: 2. 3.
4.
Set instrument parameters as required for analysis. Allow sufficient warm-up/equilibration time. Perform on-site multi-point calibration at five or more concentrations over the range 10 to 1000 ppm. a. Zero instrument while recirculating uncontaminated air through sample cell. b. Inject known volume of N 2O into the sample cell with a gas-tight syringe. NOTE: Inject the N 2O through tubing or a septum attached to the sample cell. c. Calculate concentration, C s (ppm), of N 2O in sample cell:
d. When instrument reading stabilizes, record meter or recorder deflection. e. Prepare calibration graph (C s vs. meter or recorder deflection). Practice routine instrument maintenance. a. Replace septa in a closed-loop system frequently in accordance with manufacturer's recommendations. b. Check and replace, if cloudy, the NaCl windows in the infrared spectrophotometer. NOTE: AgBr optics cloud less quickly. c. Follow manufacturer's recommendations for specific routine maintenance.
MEASUREMENT: 5. 6. 7.
Pump air to be analyzed through sample cell to purge the sample cell. Typically, 2 to 3 cell volumes are necessary. When output stabilizes, record meter or recorder reading. Read the concentration of N 2O in the unknown samples, C v (ppm), corresponding to the meter or recorder deflection directly from the calibration graph. Periodically during each day's operation recheck calibration by going to step 2 and repeating three or more points on the calibration graph.
EVALUATION OF METHOD: This method has been successfully used in hospital, dental and veterinary operatories. Calibration curves have proven reproducible. Individual data sets have demonstrated statistical comparability in Bartlett's test for homogeneity. Relative standard deviations, s r, as low as 0.006 have been seen in replicate calibrations of the same instrument by different individuals in the 10 to 1000 ppm range [1].
REFERENCES: [1] [2]
Burroughs, G. E. NIOSH, Division of Physical Sciences and Engineering, unpublished data (1983). Criteria for a Recommended Standard...Occupational Exposure to Waste Anesthetic Gases and Vapors, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 77-140 (1977).
METHOD WRITTEN BY: G. E. Burroughs and M. L. Woebkenberg, NIOSH/DPSE.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
