No abstract

Ultraviolet and ultrasound irradiation-induced redox reactions have been assessed for the determination of Se(IV), Se(VI), selenomethionine and selenocystine in model waters, enriched natural waters and soil/fly ash extracts by the hydride-generation technique with atomic absorption and fluorescence detection. Photooxidation of Se-methionine and Se-cystine into Se(IV) by UV irradiation in HCl medium (pH 0.4) can be achieved within 10 min, whilst Se(IV), the only Se species reactive towards NaBH 4 , leading to SeH 2 formation, remains unaffected. Photoreduction of Se(VI) to Se(IV) required at least 45 min under the same conditions. Higher pH values yielded incomplete conversions of the Se species into Se(IV). Se(VI) photoreduction was completely inhibited by the presence of 10 000 mg L À1 nitrate as KNO 3 . Ultrasonic oxidation of Se-cystine to Se(IV) is seen to occur, the remaining Se species remaining unaffected. According to the above redox reactions, a four-stage model for speciation of Se is proposed. The combination of these reactions could be the basis for a new speciation approach that is advantageous in terms of sensitivity and simplicity over methods involving chromatographic separations. The LOD of each Se species was 40 pg mL À1 and 2 pg mL À1 with detection by atomic absorption and fluorescence, respectively. The repeatability expressed as relative standard deviation was in the range 2-5% for natural waters and 4-10% for phosphate extracts.

A fast, sensitive, and reliable method for determination of selenium in marine biological tissues by electrothermal atomic absorption spectrometry with slurry sampling was developed. Slurries were prepared from fresh and frozen seafood samples that were previously homogenized, dried, and ground; particle sizes <100 μm were taken for analysis. A 3% (v/v) HNO3 solution containing 0.01% (v/v) Triton X-100 was used as slurry diluent. Slurries were mixed on an automated ultrasonic slurry sampler at 20% amplitude for 30 s just before an aliquot was injected into the furnace. The method was successfully validated against the following certified reference materials: NRCC CRM DORM-2 (Dogfish muscle); NRCC CRM TORT-2 (Lobster hepatopancreas); NRCC CRM DOLT-2 (Dogfish liver); and BCR CRM 278 (Mussel tissue), and was subsequently applied to determination of Se in 10 marine biological samples. The influences of the drying procedure (oven-, microwave-, and freeze-drying), matrix modifier amount, mass of solid material in cup, and pipetting sequence are discussed. The limit of determination of Se was 0.16 μg/g and the repeatability, estimated as between-batch precision, was in the range of 4–8%. Se contents in the samples ranged from 0.6 to 2.8 μg/g. The proposed method should be useful for fast assessment of the daily dietary intake of Se.