S.V. Rao

Preconcentration and speciation of inorganic and methyl mercury in waters using polyaniline and gold trap-CVAAS.

Applicability of polyaniline (PANI) has been investigated for the preconcentration and speciation of inorganic mercury (Hg(2+)) and methyl mercury (CH(3)Hg(+)) in various waters (ground, lake and sea waters). Preliminary experiments (batch) with powdered PANI for the quantitative removal of both Hg(2+) and CH(3)Hg(+) showed that the retention of Hg(2+) was almost independent of pH while a pH dependent trend from pH 1 to 12 was seen for CH(3)Hg(+) with maximum retention at pH>5. Time dependence batch studies showed that a contact time of 10min was sufficient to reach equilibrium. The K(d) values were found to be approximately 8x10(4) and approximately 7x10(3) for Hg(2+) and CH(3)Hg(+), respectively. Subsequently column experiments were carried out with PANI and the separation of the species was carried out by selective and sequential elution with 0.3% HCl for CH(3)Hg(+) and 0.3% HCl-0.02% thiourea for Hg(2+). This was then followed by further pre-concentration of mercury on a gold trap and its determination by CVAAS. The uptake efficiency studies showed that the PANI column was able to accumulate up to 100mgHg(2+)/g and 2.5mgCH(3)Hg(+)/g. This method allows both preconcentration and speciation of mercury with preconcentration factors around 120 and 60 for Hg(2+) and CH(3)Hg(+), respectively. The interfering effects of various foreign substances on the retention of mercury were investigated.

Speciation of Cr(III) and Cr(VI) in waters using immobilized moss and determination by ICP-MS and FAAS.

The possibility of using moss (Funaria hygrometrica), immobilized in a polysilicate matrix as substrate for speciation of Cr(III) and Cr(VI) in various water samples has been investigated. Experiments were performed to optimize conditions such as pH, amount of sorbent and flow rate, to achieve the quantitative separation of Cr(III) and Cr(VI). During all the steps of the separation process, Cr(III) was selectively sorbed on the column of immobilized moss in the pH range of 4-8 while, Cr(VI) was found to remain in solution. The retained Cr(III) was subsequently eluted with 10ml of 2moll(-1) HNO(3). A pre-concentration factor of about 20 was achieved for Cr(III) when, 200ml of water was passed. The immobilized moss was packed in a home made mini-column and incorporated in flow injection system for obtaining calibration plots for both Cr(III) and Cr(VI) at low ppb levels that were compared with the plots obtained without column. After separation, the chromium (Cr) species were determined by inductively coupled plasma mass spectrometry (ICP-MS) and flame atomic absorption spectrometry (FAAS). The sorption capacity of the immobilized moss was found to be approximately 11.5mgg(-1) for Cr(III). The effect of various interfering ions has also been studied. The proposed method was applied successfully for the determination of Cr(III) and Cr(VI) in spiked and real wastewater samples and recoveries were found to be >95%.

A simple UV-photolysis digestion method for the determination of fluoride in fluorine-containing drugs by ion-selective electrode and spectrophotometry techniques

A simple, effective and reliable UV photolysis digestion (UVPD) method has been developed for the determination of fluoride in pharmaceuticals containing fluorine as one of the constituents. It is based on the use of high intensity UV-irradiation in the presence of a mixture of HNO3 and methanol. For the optimization of the UVPD procedure, three bulk drug samples namely levofloxacin, nebivolol and efavirenz, were chosen as representatives of three diverse matrices: containing single fluorine, two fluorine atoms and trifluoromethyl groups respectively. Optimization of the procedure involves an initial reaction with nitric acid followed by a UVPD approach for complete mineralization of the sample i.e., conversion of bound fluorine to free fluoride ion followed by determination by fluoride ion-selective electrode (F-ISE) and spectrophotometry based methods. Parameters affecting the UVPD method, such as acid concentration, digestion time and sample weight, were optimized to obtain the quantitative recovery (>95%) of fluoride. Quantitative recovery of the fluorine in the samples could be achieved within 20–30 min of UV exposure time for a 50-mg sample. Total digestion of the drug samples was carried out by a closed microwave digestion system and the recoveries of the fluoride were found to be low (<70%) demonstrating the capabilities of the UVPD procedure. The proposed UVPD method was successfully applied to various commercially available fluorine containing drug samples.

Ultrasound-assisted analyte extraction for the determination of sulfate and elemental sulfur in zinc sulfide by different liquid chromatography techniques.

The speciation and determination of sulfate (SO4(2-)) and elemental sulfur (S degree) in zinc sulfide (ZnS) using ion-chromatography (IC) and reversed-phase liquid chromatography (RPLC) respectively is described. Three sample pretreatment approaches were employed with the aim of determining sulfate: (i) conventional water extraction of the analyte; (ii) solid-liquid aqueous extraction with an ultrasonic probe; and (iii) elimination of the zinc sulfide matrix via ion-exchange dissolution (IED). The separation of sulfate was carried out by an anion-exchange column (IonPac AS17), followed by suppressed conductivity detection. Elemental sulfur was extracted ultrasonically from the acid treated sample solution into chloroform and separated on a reversed phase HPLC column equipped with a diode array detector (DAD) at 264 nm. The achievable solid detection limits for sulfate and sulfur were 35 and 10 microg g(-1) respectively.

Development of a microwave-assisted digestion method for the rapid determination of chloride and fluoride in nuclear-grade boron carbide powders

A simple and efficient microwave-assisted digestion (MAD) method for the rapid determination of chloride and fluoride in nuclear-grade boron carbide powders has been developed using a closed microwave-vessel (G30, Anton Parr) and a domestic microwave oven. Parameters optimized to get quantitative recoveries of chloride and fluoride were extractant concentration, microwave power, irradiation time and amount of the sample. The optimized MAD conditions for quantitative recovery of chloride and fluoride were obtained by irradiating ∼0.5 g of sample in 10 mL of 10% HNO3 (v/v) for about 30 s at a microwave power of 480 W. After completion of the extraction process, the sample mixture was centrifuged and then a known volume of the sample extract (clear supernatant) was transferred to another pre-cleaned tube for subsequent analyses of Cl and F using an ion-selective electrode (ISE). A pyro-hydrolysis method was used for validation of the results of the proposed MAD method. The LOD values for chloride and fluoride in conjunction with the proposed MAD were found to be 1.9 μg g−1 and 1.2 μg g−1 respectively with a relative standard deviation (RSD) of less than 10%. The studies have demonstrated that the proposed microwave-based approach constitutes a good alternative sample preparation methodology for the determination of chloride and fluoride in nuclear-grade boron carbide powder samples.