Selenium Limit Test

Selenium Determine as directed in Method II under Selenium Limit Test, Appendix IIIB, using a 200-mg sample. 

Loss on Drying Determine as directed under Loss on Drying, Appendix IIC, drying a sample to constant weight at 250°. Selenium Determine as directed in Method II under Selenium Limit Test, Appendix IIIB, using a 200-mg sample. 

Selenium Determine as directed in Method II under Selenium Limit Test, Appendix IIIB, using a 1.2-g sample. Water-Insoluble Substances Dissolve 50 g of sample in 300 mL of hot water contained in a 600-mL beaker allow the insoluble matter to settle and filter by decanting through a tared, sintered-glass filter cmcible, washing the insoluble matter into the crucible with additional hot water. Dry at 100° to 110° for 1 h, cool in a desiccator, and weigh. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

A waste is toxic under 40 CFR Part 261 if the extract from a sample of the waste exceeds specified limits for any one of eight elements and five pesticides (arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, endrin, methoxychlor, toxaphene, 2,4-D and 2,4,5-TP Silvex using extraction procedure (EP) toxicity test methods. Note that this narrow definition of toxicity relates to whether a waste is defined as hazardous for regulatory purposes in the context of this chapter, toxicity has a broader meaning because most deep-well-injected wastes have properties that can be toxic to living organisms. 

The separation of selenium species by HPLC followed by either AAS or ICP-OES detection has been studied. When the column effluent has been connected directly to the nebuliser of the detector, the detection limits have not been adequate for analysis of environmental samples. The introduction of volatile derivatives such as hydrides to the detector improves the detection limits since a larger proportion of the analyte is transported to the detector. The reduction technique was applied to the determination to selenium species in seawater (Cobo-Fernandez et al., 1993). The analyses were carried out on-line using FI. The equipment included a reaction loop tested at 140°C for the reduction of Se to Se. Se was calculated as the difference between total selenium and original Se (determined without heating). The detection limit was 0.7 mg dm-3 for each species. 

Liquid absorbance standards provide a theoretically perfect way of checking the linearity of the photometric scale of an instrument because absorbance is directly proportional to concentration or path length. However, technical imperfections in instruments, cuvets, and filter solutions limit the accuracy of absolute photometric determinations (60). Liquid standards should be prepared for each calibration session. Solid samples should be checked and recertified periodically by an accredited standards testing laboratory. Color standards that change with temperature or light exposure such as the National Bureau of Standards red glass filter No. 2101 that is doped with selenium (50) must be used cautiously as recommended by the standards issuing laboratory. 

Procedure. Silver foil is roughened with fine emery paper and then thoroughly cleaned, A drop of the test solution is placed on the foil and the solvent (CSg) allowed to evaporate. A gray or black gray fleck of silver selenide appears. Limit of Identification 5 y selenium... 

---