Performance of methods for measurement of exposure to inorganic acids in workplace air

Abstract

BGIA has organised round robins for the analysis of samples of inorganic acids in workplace air for a number of years. Test samples of the volatile acids HCl and HNO(3) are collected from a standard atmosphere and samples of the non-volatile acids H(3)PO(4) and H(2)SO(4) are prepared by spiking filters with acid solution. The last two round robins have also covered the sampling of volatile acids, with up to 15 "active" participants able to visit the test facility in Dresden and take samples themselves. For other "passive" participants, BGIA takes samples from the same atmosphere. The acid concentrations generated lie between 0,1 and 1 times the German limit values for HCl and HNO(3). The results for the last round robin showed no significant difference between the performance of the "active" and "passive" participants. The participant means were in good agreement with the theoretical concentrations and the quality control measurements. For "active" participants RSDs were between 7% and 14% and for all participants between 8% and 16%. The round robin for the non-volatile acids showed similar results. The participant means were again in excellent agreement with the quality control measurements and RSDs were between 12% and 15%. The BGIA round robins have demonstrated the proficiency of laboratories measuring exposure to inorganic acids in air. However, concerns remain about the performance of published methods. It has shown that the sampling efficiency of sorbent tubes falls off with increasing particle size and hence silica gel tube methods may give low results for acid mists. Another issue with silica gel tubes is that a substantial proportion of the sample can be collected on the glass wool plugs that retain the sorbent. This can be up to 50% for HCl and 100% for HNO(3). Hence, low results may be obtained if the glass wool plugs are discarded. Similarly, methods for volatile inorganic acids that use a pre-filter to remove particulates usually overlook the fact that the acids can react with co-particulate matter on the pre-filter. Low recoveries in the range 30%-50% have been found when sampling HCl through filters loaded with potential interferents. Finally, particulate salts interfere with filter sampling methods for non-volatile inorganic acids. A two-part International Standard is in preparation for inorganic acids by ion chromatography and the issues discussed above are being taken into consideration during its development.

Evaluation of Sampling Methods for Measuring Exposure to Volatile Inorganic Acids in Workplace Air. Part 2: Sampling Capacity and Breakthrough Tests for Sodium Carbonate-Impregnated Filters

“…(7) To check if this type of reaction can also occur with acids having approximately the same strength, a final interference experiment was designed using, as a prefilter, a quartz fiber filter impregnated with either 10 mg sodium chloride (NaCl) or sodium nitrate (NaNO 3 ), and sampling the acid corresponding to the other salt through this filter. This particular mass of salt was chosen to simulate a filter having collected dust at one 8 hr-LV of low toxicity inhalable dust.…”

“…After preliminary work published in 2006, (7) the International Standards Organization (ISO) published a three-part standard (ISO 21438) (8)(9)(10) on the determination of inorganic acids in workplace air by ion chromatography (IC). During the development of Part 2 of the standard (ISO 21438-2), (9) which describes the alkali-impregnated filter method for volatile acids (except hydrofluoric acid), a series of sampling exercises were carried out by several European institutes at the test gas facility of the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) in Sankt Augustin, Germany, to characterize the performance of existing methods for sampling HCl and HNO 3 .…”

New NIOSH Methods for Sampling and Analysis of Airborne Inorganic Acids

“…(17,18) Estimated MDLs for H 2 SO 4 and H 3 PO 4 were 0.002 mg/m 3 and 0.003 mg/m 3 for a sampled air volume of 1 m 3 . Expanded measurement uncertainty obtained for both acids was <23%.…”

“…An interlaboratory study with 26 participants found negligible biases and interlaboratory relative standard deviations of 12–15% for H 2 SO 4 and H 3 PO 4 concentrations between 0.05 and 1 mg/m 3. (17) The method has also been successfully field tested for workplace H 2 SO 4 measurements at sample volumes of up to nearly 2,000 liters. (18) …”

Development and field testing of a miniaturized sampling system for simultaneous sampling of vapours and droplets

“…6 Sampling of aerosols containing SV compounds using methods like lter sampling can prove to be challenging. [7][8][9] The particles trapped on lters can readily evaporate [10][11][12] or vapours can adsorb 13 on ltration substrates, thus leading to measurement errors as a consequence.…”