Abstract
The determination of gaseous and particulate fluorides using a modified sampler and ion chromatographic (IC) analysis was examined in response to problems that were recently identified with the existing National Institute for Occupational Safety and Health (NIOSH) Method 7902, “Fluorides, Aerosol and Gas.” After development of the new sampler and IC technique, the modified method was compared to the existing method, which is based on ion selective electrode potentiometry (ISE). The sampling train that was recommended in NIOSH Method 7902 was modified to a 37-mm cassette with a 0.8-μm mixed cellulose ester filter, which is supported by a porous plastic pad in the front section and an alkaline treated cellulose pad in the rear section; these sections are separated by a half-inch extension. The IC analysis employed a Dionex AS4A column, AG4A guard column, and conductivity detection (Dionex Corp., Sunnyvale, California). The sodium tetraborate eluant was the only eluant of four that were tested which resolved fluoride from all the peaks expected in typical workplace samples. The sampler modification helped prevent the loss of gaseous fluoride. The IC technique results in an estimated limit of detection of 3 μg/sample for gaseous fluoride and 120 μg/sample for particulate fluoride. When the IC Analytical procedure was compared to the existing ISE procedure of NIOSH Method 7902, the IC procedure was found to be equivalent when determining gaseous fluoride. When determining particulate fluoride on laboratory prepared samples, the ISE procedure underestimated the fluoride loading by 8.1 percent at 500 μg/ sample (and 15.6% at 200 μg/sample) while the IC procedure overestimated the fluoride level by 8.5 percent at 500 μg/sample (and 15.5% at 200 μg/sample). The IC procedure was more resistant to metal ion (aluminum) interference than the ISE procedure. Although the presence of aluminum ions further depressed the response to fluoride with the ISE analysis, the IC results were not changed. In tests that examined the interaction of hydrogen fluoride with dust, only small losses (12 μg or less, based on total loadings of 205 and 125 μg) of hydrogen fluoride were observed, with as much as 5.8 mg of aluminum oxide on the front stage. The IC analysis procedure should be considered to be a complementary part of NIOSH Method 7902 and, therefore, was added as an option to Method 7902 in the fourth supplement (Aug. 15, 1990) to the third edition of the NIOSH Manual of Analytical Methods.
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Charles Lorberau
Lorberau, C.: Determination of Gaseous and Particulate Fluorides by Ion Chromatographic Analysis. Appl. Occup. Environ. Hyg. 8(9):775–784; 1993.