Nitric acid filter pack measurement

Filters. HN03 is efficiently trapped out on nylon filters. Typically, two or more filters are connected in series. A schematic of such a filter pack was shown in Fig. 11.22 (Anlauf et al., 1988). A Teflon filter first removes particles from the airstream and a nylon filter then removes gaseous HNO,. In this particular system, a third filter (Whatman 41 impregnated with an aqueous solution of glycerol and citric acid) was used to trap NH3. After sample collection, each of the filters is extracted separately and nitrate, ammonium, and additional particle components collected on the Teflon filter are measured by ion chromatography. The sensitivity of this method for nitric acid and the other species is determined in part by filter blank values (i.e., nitrate on unexposed filters) and by the total amount collected and hence the sampling time used. Times of... 

Filter packs. As shown in Fig. 11.22, NH3 can be collected on impregnated filters in filter packs designed to collect particles and gas-phase nitric acid. Oxalic acid or citric acid on Whatman filters is often used to absorb the gaseous ammonia, which is then measured by extraction into aqueous solution and ion chromatography or by a colorimetric method (e.g., see Anlauf et al., 1988 and Williams et al., 1992). 

The test and standaid samples are irradiated in a nuclear reactor. After dissolution in the presence of 12 mmol fluorine carrier, the solution is adjusted to pH 8-9. The hydrated silicon dioxide precipitate is filtered and the acidity of the filtrate is adjusted to IM nitric add. Then it is passed through a column packed with hydrated tin dioxide. The radioactivity of the column is measured. The oxygen content is calculated from the activities of the test and standard samples. This method is easy and quick, and is suitable for determinations of trace amounts of oxygen. 

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