Selenium speciation—a flow injection approach employing on-line microwave reduction followed by hydride generation–quartz furnace atomic absorption spectrometry

Abstract

Trace and ultra-trace levels of selenium are routinely determined in many laboratories using hydride generation-quartz furnace atomic absorption spectrometry. However, as more is understood about the role of selenium in toxicity and dietary studies, there is an increasing need to provide species-specific information from complex biological and environmental samples. As the hydride generation process requires the selenium to be in the selenium(1v) oxidation state, prior reduction of any selenium(vr) present in the sample is necessary. This step is conventionally accomplished by maintaining the sample at an elevated temperature in the presence of hydrochloric acid, although this approach suffers from a number of disadvantages, including the loss of information on the original selenium species present in the sample. This paper describes an on-line system for the determination of inorganic selenium species in which the sample is first analysed for selenium(~v), and then microwave energy is then used to reduce selenium(v1) and provide a total selenium measurement. As full control of the microwave reduction step is possible, the approach lends itself to a totally automated selenium speciation system. Detection limits and precision are unaffected by the on-line reduction step.

Indirect Spectrophotometric Determination of Small Amounts of Selenium(IV) and Arsenic(V) by Simple Extraction Using Flotation Columns

“…For polluted water, a 250 cm 3 solution was heated with a 10 cm 3 portion of (1:1) perchloric and aqua regia to dryness. The residue was dissolved and completed to 25 cm 3 with 4 mol dm -3 HCl.…”

“…Therefore, precise knowledge of the selenium and arsenic compounds present in a system is required for an accurate assessment of the environmental and biological impact of selenium and arsenic, which have resulted in an increasing need of analytical methods for their determination at microtrace or even ultra-trace levels. Although an excellent group of papers has been published 2,3,7,11,[17][18][19][20][21][22][23][24][25][26][27] describing sensitive techniques used for the indirect spectrophotometric determination of Se and As, spectrophotometry still represents an attractive technique for the determination of metal ions in aqueous media because of its simplicity, being inexpensive and more readily available. Therefore, the present investigation aims to present a sensitive, simple, and rapid procedure for the indirect spectrophotometric determination of Se(IV) and As(V) after reduction with KI in an HCl medium, extracting the equivalent iodine with HOL surfactant and measuring the I2-HOL system at 435 nm.…”

“…[1][2][3][4] For example, selenium compounds have been reported to have anticarcinogenic activity and to prevent heavy-metal toxic effects. [5][6][7] On the other hand, an excessive intake of selenium can lead to toxic responses, including alkali disease and blind staggers.…”

Speciation of Selenium Compounds

“…10 This process can be also performed using microwave heating. 11 The generated selenium hydride is enriched into a liquid nitrogen cold trap and then swept into a flame or electrically heated quartz tube or into a graphite furnace for detection.…”

Simultaneous detection of selenium by atomic fluorescence and sulfur by molecular emission by flow-injection hydride generation with on-line reduction for the determination of selenate, sulfate and sulfite

“…As noted above, selenium species must be reduced to the Se(IV) state prior to the hydride generation stage. The reduction of Se(VI) to Se(IV) by hydrochloric acid in a flow-injection manifold has been reported [20][21][22]. For organo-selenium compounds an oxidation step is required to covert the selenium to selenium (VI) prior to reduction.…”