A highly sensitive method was investigated for the determination of selenium in the atmosphere at trace levels using HPLC and a fluorescence detection system. The sample was decomposed with nitric acid and hydrogen peroxide. After the wet digestion, selenium exists predominantly in the form of selenium(VI). Therefore, it is necessary to reduce selenium(VI) to selenium(IV) before the 2, 3-diaminonaphthalene (DAN)-selenium(IV) reaction. However, nitric acid remaining in the sample solution interferes with the reduction of selenium(VI). In order to eliminate the interference by nitric acid, it was evaporated to near dryness after adding 1 ml of perchloric acid. After adding 5 ml of 6 M hydrochloric acid to the sample solution and the mixture was heated in a boiling water bath for 30 min to reduce selenium(VI) to selenium(IV), then warmed with 5 ml of 0.1% DAN and 1 ml of 0.1 M EDTA-NaF at 50°C for 20 min to form a piazselenol. The complex was extracted with 1 ml of cyclohexane. A 100 µl aliquot of the cyclohexane layer was analyzed by HPLC on a column (UNISIL ODS) with a mixture of cyclohexane and tetrahydrofuran (90/10, v/v) as the mobile phase. Se-DAN complex was fluorometrically detected with excitation at 375 nm and fluorescence at 520 nm. This method was applied to the standard sample of Vehicle Exhaust Particulates (NIES No. 8). The analytical result was in good agreement with the certified value. The detection limit of this method was 10pg/m3 for a 30 m3 air sampling volume. Therefore, this method can be satisfactorily applied to the determination of selenium in the atmosphere at trace levels.
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