An analytical method was developed for the determination of ammonia (7664417) concentrations in air. A known volume of air was drawn through a tube containing 20/40 mesh silica gel treated with sulfuric-acid to trap the ammonia vapors. The ammonia was desorbed from the silica gel with sulfuric-acid, and the sample was separated and analyzed using an ammonia specific electrode. The method was validated over a range of 16.9 to 67.6 milligrams per cubic meter (mg/m3) for a 30 liter sample. Testing was performed by analyzing 18 samples spiked with 50, 100, or 200 percent of the OSHA standard of 35mg/m3, or 18 samples collected from dynamically generated test atmospheres. The breakthrough capacity of the treated silica gel, the storage stability of the samples, and the precision and accuracy of the method were determined. Breakthrough did not occur at any of the concentrations tested. Concentrations found immediately after testing and after 7 days were 32.5 and 33.6mg/m3, respectively. The total coefficient of variation was 0.062; concentrations obtained were about 2.4 percent lower than actual values for the 18 samples. The authors conclude that the advantages of the method are that it is small, portable, and involves no liquids. The tubes are analyzed by a quick, instrumental method. One disadvantage is that the amount of sample is limited by the capacity of the tube. The precision is limited by the reproducibility of the pressure drop across the tubes.
Ten NIOSH Analytical Methods, Set-6, Division of Physical Sciences and Engineering, NIOSH, Cincinnati, Ohio, NTIS PB-288-629, 25 pages, 5 references