No abstract available

No abstract available

[en] Because of the increasing interest as to their roles in biological systems, a procedure has been developed by which molybdenum and selenium can be determined at nanogram levels in these types of samples. Results from the analysis of orchard leaves and bovine liver are presented. The samples are packaged in pre-cleaned quartz vials prepared from GE-204 tubing. If both selenium and molybdenum are to be determined, the samples are irradiated for 40 or more hours at a thermal neutron flux of 8 x 10¹³n cm^-2 sec^-1. After the samples have decayed for approximately 48 hours the vials are unpackaged, cleaned in aqua-regia, and broken. The irradiation period can be reduced to 24 hours if molybdenum is to be determined individually or if the selenium content is known to be 1 microgram or more. The sample is digested with carriers and the selenium is then distilled as a volatile selenium halide. Elemental selenium is precipitated by reduction with SO₂ produced through the protonation of the hydrogen sulfite ion and subsequent decomposition of the resulting sulfurous acid. The 401 keV summation peak of ⁷⁵Se is normally used for quantitative determination. The chemical yield is determined by drying and weighing the elemental selenium

No abstract available

[en] Highly sensitive procedures for the determination of chromium in bio-environmental samples using neutron activation analysis, atomic absorption and gas chromatography have been developed in this laboratory. In the neutron activation procedure, dried samples are irradiated for up to 100 hours at a neutron flux in excess of 10¹⁴ neutrons cm^-2s^-1 for determinations at the parts per 10⁹ level. Following irradiation, chromium is separated by distillation as chromylchloride and precipitated and counted as BaCrO₄. Samples to be analysed by atomic absorption were digested using concentrated nitric acid followed by hydrogen peroxide, and injected into a Perkin Elmer model 2100 graphite furnace. For the gas chromatography determinations an EC detector in pulse mode with linearizer was used to detect chromium trifluoroacetylacetonate following separation on 3% OV-17. Analysis of a round-robin, freeze-dried urine sample by all three methods gave excellent agreement. (author)

No abstract available

[en] Three different pre-irradiation separation NAA methods have been developed and tested for the determination of vanadium in wet-ashed marine biological samples and dissolved or acid-leached marine sediment and suspended particulate samples. Also, a post-irradiation carrier separation of ¹³⁹Ba procedure has been developed and tested. All of the methods developed have been shown to be efficient, as well as much more sensitive than a purely instrumental NAA technique for these two elements, in such matrices