Determination of selenium by activation analysis and dry volatilization

Abstract

The use of selenium in stainless steels and the importance of selenium in biological materials and processes have been discussed in the literature (1-6). However, the separation and determination of selenium in these materials by conventional chemical methods can be difficult, tedious, and, if care is not exercised, subject to inaccuracies due to volatilization (1, 4-10). Neutron activation analysis techniques also have been used for the determination of selenium (2, 5). Generally, the production of 120-day 78Se, 17.4-second 77™Se, and 18.6-minute 81sSe has been used for the analysis (2). However, with selective dry distillation techniques, standard radiochemical procedures are not required and quantitative recovery is possible. The radiochemistry of selenium has been discussed by Leddicotte (11) and DeVoe (12).In the method reported here, the selenium-containing sample and a standard are irradiated by either thermal neutrons or by 14-MeV neutrons. The selenium is then separated by a dry distillation technique and is determined by counting the gamma rays of 121-day 75Se or 57-minute 81"'Se. This method also permits the qualitative identification of selenium by the appearance of the metal in the dry distillation collection tube. The various known neutron reactions which can occur are given elsewhere (13-15). EXPERIMENTAL Apparatus and Reagents. The counting system included a 3-X 3-inch Nal(Tl) crystal, with associated electronics, connected to a Technical Measurements Corp. 400-channel analyzer.Thermal neutron irradiations of samples were performed in the Sandia Reactor Facility (SRF) in a position which had

Single scale for ion activities and electrode potentials in ethanol-water solvents based on the triisoamylbutylammonium tetraphenylborate assumption

“…We have shown elsewhere (12) that the function H0 may serve as a fair approximation of paH in alcohol-water media. Based on this assumption, log myH can be approximated for ethanol-water solvents from the H0 data of Braude and Stern reported for 0.1M solutions of HC1: log rriJn = -H0log Whcilog «HCllog s7h (8) where mHc) and auc, are the analytical molality and the degree of dissociation of HC1, respectively. The curve in Figure 1 represents such estimates of log ",7 calculated in the form ( -H0 -log Whci)• Values of log m7H from this study (Table IV) are shown as individual points.…”

“…This provides the basis for the assumed solvent-independence of the £°'s of the substituted-ferroin electrodes (24)(25)(26). The disadvantages in using redox couples of the +2/+3 charge type have been pointed out (8).…”

“…Tetraphenylarsonium tetraphenylborate is the most recent choice (6,29). The weak points in themethods based on reference counterions are insufficient evidence for the equality of their ionic radii (8) and the possible formation of crystal solvates (6). So far, the approximate equality in the size of the reference ions was deduced from models (28) or from Stokes radii (4).…”

“…Corrections could be made for the formation of crystal solvates, if any, though it is doubtful that they would amount to appreciable energies for the reference ions, in which the medium effects are determined predominantly by their large neutral components. It has been argued that methods based on the splitting of the solvation energy of an electrolyte between its counterions should not be applied to dipolar aprotic solvents, which differentiate strongly between the relative solvation of anions and cations (8). However, only extensive experimental work will show whether arguments based on the behavior of small inorganic ions can be extended to the large organic reference ions, whose (28) E. Grunwald, G. Baughman, and G. Kohnstam, J. Amer.…”

Determination of Cadmium, Lead and Selenium in Medicago sativa Herb by Differential Pulse Stripping Voltammetry

“…7,8 Other accessible techniques capable of multielement determination, such as atomic emission spectrometry with inductively coupled plasma excitation (AES-ICP) and X-ray fluorescence (XRF), are very expensive and often do not offer sufficient sensitivity for accurate determination of most elements at the trace to ultratrace concentrations usually encountered in biological and environmental samples. Voltammetric techniques such as differential pulse polarography (DPP) 9,10 , anodic stripping voltammetry (ASV) 11,12 , cathodic stripping voltammetry (CSV) 13,14 and the more recent approach of adsorption voltammetry (AV) 15,16 require relatively inexpensive instrumentation, are capable of determining elements accurately at trace to ultratrace levels and have demonstrated ability for multielement determination.…”