Direct Speciation of Selenite and Selenate with Thermospray Sample Introduction Methods

Facile and sensitive determination of selenium (IV) in pharmaceutical formulations by flow injection spectrophotometry

An automated flow injection spectrophotometric method has been developed for the rapid, simple, selective, and sensitive determination of selenium (IV) from various pharmaceutical multivitamin and mineral formulations. The method was based on the oxidation of 4-aminoantipyrine (4-amino-l,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazole-3-one; 4-AAP) by selenium in presence of acidic medium and the coupling with N-(naphthalen-l-yl)ethane-1,2-diamine dihydrochloride (NEDA) to give a violet color derivative. Gilson P2 mini pulse peristaltic pump has been used for introducing the selenium (IV), dilute HCl, 4-AAP and NEDA solutions into reaction coil by an automatic system. The absorbance of the 4-AAP-NEDA color derivative was measured at 563 nm after a reaction time of 3 min in stop flow of 4-AAP-NEDA. Beer's law was obeyed for selenium in the concentration range 0.05-5.0 microg mL(-1) and Sandell's sensitivity was found to be 0.00286 microg cm2. The performance of the present method was compared with the official method in terms of Student's F- and t-tests, and no significant difference was observed. This method was found to be suitable for estimating the selenium (IV) concentration in various pharmaceutical multivitamin and mineral formulations such as tablets and capsules.

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.

Indirect spectrophotometric determination of small amounts of selenium(IV) and arsenic(V) by simple extraction using flotation columns

A simple, rapid and selective procedure for the indirect spectrophotometric determination of Se(IV) and As(V) has been developed. It is based on the reduction of Se(IV) to Se(0) and As(V) to As(III) with hydroiodic acid (KI + HCl). The liberated iodine, equivalent to each analyte, is quantitatively extracted with oleic acid (HOL) surfactant. The iodine-HOL system exhibits its maximum absorbance at 435 nm. The different analytical parameters affecting the extraction and determination processes have been examined. The calibration graphs were found to be linear over the ranges 5-120 and 0.25-20 ppm of Se(IV) and As(V), with lower detection limits of 2.5 and 0.15 ppm and molar absorptivities of 1 x 10(4) and 0.5 x 10(4) dm3 mol(-1) cm(-1), respectively. Sandell's sensitivity was calculated to be 0.0078 and 0.0149 microg/cm2 in the same order. The relative standard deviation for five replicate analyses of 40 ppm Se(IV) and 4 ppm As(V) were 1.0 and 0.9%, respectively. The proposed procedure in the presence of EDTA as a masking agent for foreign ions has been successfully applied to the determination of Se(IV) in a reference sample and As(V) in copper metal, in addition to their determination in spiked and polluted water samples.