Vimlesh Chand

Trace determination and chemical speciation of selenium in environmental water samples using catalytic kinetic spectrophotometric method

A catalytic kinetic method is described for the determination of Se(IV), Se(VI) and total inorganic selenium in water based on the catalytic effect of Se(IV) on the reduction of bromate by hydrazine dihydrochloride in acidic media. The generated bromine decolorized methyl orange (MO) and the reaction was monitored spectrophotometrically at 507 nm as a function of time. The initial rate and fixed time methods were adopted for the determination and speciation of inorganic selenium. Under two optimum conditions, the calibration graphs are linear in the range 0-126.3 and 0-789.6 microg L(-1) of Se(IV) for the initial rate method and 0-315.8 and 0-789.6 microg L(-1) of Se(IV) for the fixed time method. The detection limits were 1.3 and 14.7 microg L(-1) for the initial rate and fixed time methods, respectively. The proposed methods were validated statistically and through recovery studies in environmental water samples. The relative standard deviation in the determination of 31.6-94.8 microg L(-1) of Se(IV) and Se(VI) was less than 6%. Analyses of standard reference materials for selenium using initial rate and fixed time methods showed that the proposed methods have good accuracy. Se(IV), Se(VI) and total inorganic selenium in environmental water samples have been successfully determined by this method after selective reduction of Se(VI) to Se(IV).

Distribution and chemical fractionation of arsenic in surficial sediments of the Lami coastal environment in Fiji.

A case of arsenic contamination has recently been detected in the Lami coastal environment during the course of a heavy metal monitoring in Fijis coastal environment. Twenty two surficial sediment samples were sampled during the 2008–2009 period, extracted for arsenic and analysed using graphite furnace atomic absorption spectrometry. Two sites within the Lami estuary recorded the highest As levels of 334 and 282 mg kg–1 as dry weight in sediments samples, which has greatly exceeded the local and global average background concentrations. Chemical fractionation studies using a standard sequential protocol showed that As is mostly associated with residual (strong acid extractable) phase of the sediments, however significant amounts of As were also detected in bioavailable (exchangeable, water and acid soluble), reducible and oxidisable fractions. Comparison with standard sediment quality guidelines (SQGs) indicate that As levels are likely to be highly toxic to biota, hence further ecotoxicological studies are warranted to evaluate possible environmental effects on the aquatic environment.

High coordination compounds of Dioxouranium(VI) derived from Schiff Bases of 4-Aminoantipyrine

Uranium(VI) is very prominent in its complexation tendency, especially when it forms compounds exhibiting high coordination numbers. A metal acquires a high coordination number when (a) it is a small and highly charged ion with suitable vacant orbital of right energy, (b) it can attain a noble gas structure (effective atomic rule), and (c) it can attaina symmetrical shape and high CFSE in complex. U(VI) ion has positive charge which is one of the essential conditionsfor high coordination, as it will not allow the negative charge donated by electrons from the ligands to accumulate on the central metal ion. U6+ successfully reveals high coordination numbers 6 to 10. The examples of different coordination numbers of UO2 2+ coordination compounds are available in literature, many of which have been reported from our laboratory. We have synthesized and reported a number of high coordinated complexes of UO2 2+ with Schiff bases. All the coordination compounds reported herein have been suitably characterized by various physico-chemical techniques. The present review summarizes mostly our work on the UO2 2+ complexes of Schiff bases 4-aminoantipyrine, including 4-aminoantipyrine derived semicarbazones, thiosemicarbazones and some mixed ligand complexes.