D. Karunasagar

A combined treatment approach using Fenton’s reagent and zero valent iron for the removal of arsenic from drinking water

Studies on the development of an arsenic remediation approach using Fentons reagent (H2O2 and Fe(II)) followed by passage through zero valent iron is reported. The efficiency of the process was investigated under various operating conditions. Potable municipal water and ground water samples spiked with arsenic(III) and (V) were used in the investigations. The arsenic content was determined by ICP-QMS. A HPLC-ICPMS procedure was used for the speciation and determination of both As(III) and (V) in the processed samples, to study the effectiveness of the oxidation step and the subsequent removal of the arsenic. The optimisation studies indicate that addition of 100 microl of H2O2 and 100 mg of Fe(II) (as ferrous ammonium sulphate) per litre of water for initial treatment followed by passing through zero valent iron, after a reaction time of 10 min, is capable of removing arsenic to lower than the US Environmental Protection Agency (EPA) guideline value of 10 microg/l, from a starting concentration of 2 mg/l of As(III). Using these suggested amounts, several experiments were carried out at different concentrations of As(III). Residual hydrogen peroxide in the processed samples can be eliminated by subsequent chlorination, making the water, thus, processed, suitable for drinking purposes. This approach is simple and cost effective for use at community levels.

Determination of elemental constituents in different matrix materials and flow injection studies by the electrolyte cathode glow discharge technique with a new design

An open-to-air type electrolyte cathode discharge (ELCAD) has been developed with a new design. The present configuration leads to a stable plasma even at low flow rates (0.96 mL/min). Plasma fluctuations arising from the variations in the gap between solid anode and liquid cathode were eliminated by providing a V-groove to the liquid glass-capillary. Cathode (ground) connection is given to the solution at the V-groove itself. Interfaced to atomic emission spectrometry (AES), its analytical performance is evaluated. The optimized molarity of the solution is 0.2 M. The analytical response curves for Ca, Cu, Cd, Pb, Hg, Fe, and Zn demonstrated good linearity. The limit of detections of Ca, Cu, Cd, Pb, Hg, Fe, and Zn are determined to be 17, 11, 5, 45, 15, 28, and 3 ng mL(-1). At an integration time of 0.3 s, the relative standard deviation (RSD) values of the acid blank solutions are found to be less than 10% for the elements Ca, Cu, Cd, Hg, Fe, and Zn and 18% for Pb. The method is applied for the determination of the elemental constituents in different matrix materials such as tuna fish (IAEA-350), oyster tissue (NIST SRM 1566a), and coal fly ash (CFA SRM 1633b). The obtained results are in good agreement with the certified values. The accuracy is found to be between 7% and 0.6% for major to trace levels of constituent elements and the precision between 11% and 0.6%. For the injection of 100 microL of 200 ng mL(-1) mercury solution at the flow rate of 0.8 mL/min, the flow injection studies resulted in the relative standard deviation (RSD) of 8%, concentration detection limit of 10 ng/mL, and mass detection limit of 1 ng for mercury.

Gum kondagogu reduced/stabilized silver nanoparticles as direct colorimetric sensor for the sensitive detection of Hg2+ in aqueous system

A highly sensitive and selective method is reported for the colorimetric detection of Hg(2+) in aqueous system by using label free silver nanoparticles (Ag NPs). Ag NPs used in this method were synthesized by gum kondagogu (GK) which acted as both reducing and stabilizing agent. The average size of the GK-Ag NPs was found to be 5.0 ± 2.8 nm as revealed by transmission electron microscope (TEM) analysis and the nanoparticles were stable at various pH conditions (pH 4-11) and salt concentrations (5-100 mM). The GK reduced/stabilized Ag NPs (GK-Ag NPs) were directly used for the selective colorimetric reaction with Hg(2+) without any further modification. The bright yellow colour of Ag NPs was found to fade in a concentration dependent manner with the added Hg(+) ions. The fading response was directly correlated with increasing concentration of Hg(2+). More importantly, this response was found to be highly selective for Hg(2+) as the absorption spectra were found to be unaffected by the presence of other ions like; Na(+), K(+), Mg(2+), Ca(2+), Cu(2+), Ni(2+), Co(2+), As(3+), Fe(2+), Cd(2+), etc. The metal sensing mechanism is explained based on the turbidometric and X-ray diffraction (XRD) analysis of GK-Ag NPs with Hg(2+). The proposed method was successfully applied for the determination of Hg(2+) in various ground water samples. The reported method can be effectively used for the quantification of total Hg(2+) in samples, wherein the organic mercury is first oxidized to inorganic form by ultraviolet (UV) irradiation. The limit of quantification for Hg(2+) using the proposed method was as low as 4.9 × 10(-8) mol L(-1) (50 nM). The proposed method has potential application for on-field qualitative detection of Hg(2+) in aqueous environmental samples.

Study of mercury pollution near a thermometer factory using lichens and mosses

Mercury has a widespread environmental distribution, originating both from anthropogenic and natural processes. Once in the air, mercury can be widely dispersed and transported to longer distances. In the environment mercury can exist in a number of physical and chemical forms with toxicity is well known to be highly dependent on chemical form (Clarkson, 1997). As a consequence, considerable effort and progress has been made in the development of techniques for the separation and identification of individual mercury species in environmental samples (Sanchez Uria and SanzMedel, 1998). Biomonitoring using lichens and mosses is an effective method for assessing the levels of atmospheric trace element pollution including mercury (Merian, 1991; Conti and Cecchetti, 2001; Horvat et al., 2000) as lichens and mosses pick up nutrients directly from ambient air and deposition retaining many trace elements (Ruhling and Tyler, 1968). In this work, mercury contamination due to a mercury thermometer-making factory situated in the hill station Kodaikkanal (about 2120 m above mean sea level), in a southern state of India, was investigated using lichen (Parmelia sulcata) and moss (Funaria hygrometrica) samples. The content of mercury in these samples collected from different sites was determined using CV-AAS mercury analyzer and ICP–QMS in order to obtain information on the extent of mercury contamination. As mercury undergoes extensive transformation into various forms as it cycles among the atmosphere, land and water (Ebadian et al., 2001), we have carried out investigations to establish the chemical form of mercury—elemental (Hg), inorganic (Hg) or organic—in these chosen biomonitors.

Dispersive liquid–liquid micro extraction of uranium(VI) from groundwater and seawater samples and determination by inductively coupled plasma–optical emission spectrometry and flow injection–inductively coupled plasma mass spectrometry

A dispersive liquid–liquid microextraction (DLLME) method was developed for the determination of uranium(VI) in groundwater/seawater by inductively coupled plasma–optical emission spectrometry (ICP–OES) and flow injection–inductively coupled plasma mass spectrometry (FI–ICPMS). This is the first report on the extraction of uranium(VI) by a DLLME method. In this method, uranium(VI) was complexed with ammonium pyrrolidine dithiocarbamate (APDC) in the presence of cetyltrimethyl ammonium bromide (CTAB), which enhanced the hydrophobicity of the ion–association complex resulting in improved extraction into chloroform. The extraction was carried out after adjusting the pH of the water sample to 1. The uranyl ion was back extracted from chloroform layer with nitric acid for determination by ICP–OES/FI–ICPMS. Some effective parameters for complex formation and extraction, such as volume of extraction and disperser solvent, extraction time, pH and concentration of the chelating agent and surfactant have been optimized using ICP–OES. Under optimum conditions, enrichment factors of 11 and 25 were obtained from 10 mL of water sample for determinations by ICP–OES and FI–ICPMS respectively. The calibration graphs were linear in the range of 5–200 μg L−1 and 50–5000 ng L−1 with limits of detection of 2.0 μg L−1 and 30 ng L−1 respectively for ICP–OES and FI–ICPMS. The method has been applied to a few groundwater and seawater samples. The recoveries obtained for uranium(VI) in groundwater and seawater samples spiked to levels of 10 and 5 μg L−1 were 90–105% respectively. The results obtained by the proposed method have been cross validated by laser fluorimetry.

Dispersive liquid–liquid micro-extraction for simultaneous preconcentration of 14 lanthanides at parts per trillion levels from groundwater and determination using a micro-flow nebulizer in inductively coupled plasma-quadrupole mass spectrometry

This paper reports on the simultaneous extraction and preconcentration of 14 lanthanide (rare earth) elements in groundwater by a dispersive liquid–liquid microextraction (DLLME) method and their determination by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). A low flow rate (200 μL min−1) SeaSpray™ micro-flow nebulizer was used for the sample introduction. In this method, the rare earth elements are complexed with 2,6-pyridinedicarboxylic acid (2,6-PDCA) in the presence of Aliquat® 336 (tricaprylmethylammonium chloride), which enhanced the hydrophobicity of the ion-association complex, resulting in its improved extraction into chloroform. The extraction was carried out after adjusting the pH of the water sample to 4. The rare earth ions were back extracted from the chloroform layer with nitric acid for determination by ICP-QMS. Some effective parameters for complex formation and extraction, such as volume of extractant/disperser solvent, extraction time, pH and concentration of the chelating agent and surfactant, have been optimized. Under optimum conditions, an average preconcentration factor of 97 was obtained for 50 mL of water sample for determination by ICP-QMS. The calibration graphs were linear in the range of 1–100 ng L−1 for the 14 REEs, with limits of detection ranging from 0.05–0.55 ng L−1. The precision ranged from 1–5% R.S.D. (n = 3), when processing 50 mL aliquots of groundwater. The method has been applied to a few groundwater samples. The recoveries obtained for the rare earth elements in groundwater samples spiked to 10 ng L−1 were 92–109%.

Determination of mercury in hepatitis-B vaccine by electrolyte cathode glow discharge atomic emission spectrometry (ELCAD-AES)

A simple, rapid and sensitive method has been developed for the determination of mercury in Hepatitis-B vaccine samples using electrolyte cathode glow discharge atomic emission spectrometry (ELCAD-AES). This method obviates the need of any sample digestion, except simple dilution followed by analysis of the vaccine samples. Analytical performance of the ELCAD-AES for the inorganic as well as the organic mercury (methyl and thiomersal mercury) in the aqueous solutions is investigated. Biological certified reference materials, Tuna fish-IAEA-350 and Tuna fish-BCR-463 are examined for the applicability of ELCAD-AES to quantify the mercury. These results show an accuracy of between 0.6 to 2.1% with an analytical precision expressed as relative standard deviation (RSD%) of between 3 to 7% based on the multiple measurements on multiple sample loadings. In the absence of any CRM of the vaccine sample, the method has been validated by analyzing the same samples by Cold vapour-AAS and Electrothermal-AAS. Accuracy of the ELCAD results for vaccine samples is determined to be within 2 to 9% at various levels of mercury. Detection limit of the method is found to be 25 ng mL−1 and the analytical precision is between 2–5%.

On-line speciation of inorganic arsenic in natural waters using polyaniline (PANI) with determination by flow injection-hydride generation-inductively coupled plasma mass spectrometry at ultra-trace levels

A home made PTFE micro-column loaded with polyaniline (50mg), prepared freshly by a chemical method was used for the on-line separation of arsenite [As(III)] and arsenate [As(V)] followed by determination at ultra trace levels in natural waters by flow injection-hydride generation-inductively coupled plasma mass spectrometry (FI-HG-ICPMS). The species were determined using time resolved mode of data acquisition, by monitoring 75As. The volume of sample injected was 100μl. Both the species eluted within 3min. The effects of variation in sample pH, eluent concentration and the hydride generation conditions were investigated. The calibration in the range of 0.5–50μg L−1 was found to be linear with a regression coefficient, R2 ≥ 0.997. The detection limits (3σ) were calculated to be 0.05 and 0.09μg L−1 for As(III) and As(V) respectively and the precision (%RSD) at 1μg L−1 level was found to be 2.0% for As(III) and 2.5% As(V). The method validation was carried out by analyzing two BCR groundwater certified reference materials, BCR609 and BCR610, certified for total arsenic. The developed speciation method has been applied to groundwater samples collected from West Bengal, India, where there have been many instances of arsenic contamination.

A cost-effective and rapid microwave-assisted acid extraction method for the multi-elemental analysis of sediments by ICP-AES and ICP-MS

A very simple, cost-effective and rapid single-step microwave-assisted leaching procedure using screw-capped polypropylene (PP) tubes and a domestic microwave oven has been developed for the extraction of elements from sediments followed by their analysis using inductively coupled plasma spectrometric techniques (ICP-AES/ICP-MS). Parameters affecting the microwave-assisted extraction such as extractant concentration, microwave irradiation time, microwave power and sample amount were optimized to get quantitative recovery of elements by taking two certified reference materials: stream sediment GBW-7312 and marine sediment IAEA-433. The supernatant obtained upon centrifugation was used for analysis of various elements: Na, K, Ca, Mg, Fe, Al, Li, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, As, Sr, Mo, Ag, Cd, Sn, Sb, Cs, Ba, Tl, Pb and Bi. Quantitative recoveries of elements of interest were obtained using a mixture of 30% HNO3 + 5% HF with 30 s irradiation time at a microwave power of 640 W for <500 mg sample weight. The results obtained here were in good agreement with the certified values with an overall precision of better than 10%. The obtained results showed that the present method of microwave assisted leaching (employing 30% HNO3 + 5% HF) of sediment reference materials without resorting to total digestion produced an efficient attack of the most important metal bearing mineral phases and the quantitative recoveries obtained here showed complete leaching of the elements of interest. The procedure is especially attractive as it requires a microwave irradiation time of less than a minute and is thus extremely rapid.

Dispersive liquid–liquid micro extraction of boron as tetrafluoroborate ion (BF4−) from natural waters, wastewater and seawater samples and determination using a micro-flow nebulizer in inductively coupled plasma-quadrupole mass spectrometry

Boron, present in groundwater and seawater, is extracted as tetrafluoroborate anion by dispersive liquid–liquid microextraction (DLLME) and determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). A low flow rate (200 μL min−1) SeaSpray™ micro-flow nebulizer was used for the sample introduction. In this method, the tetrafluoroborate anion formed in the presence of 0.9 mol L−1 H2SO4 and 0.1 mol L−1 F− was extracted into chloroform in the presence of Aliquat® 336 (tricaprylmethylammonium chloride) at room temperature. The bulky cationic surfactant, Aliquat® 336, acts as a phase transfer agent, which not only forms an ion-pair complex with tetrafluoroborate anion but also helps in the rapid conversion of boric acid to BF4− ion. The tetrafluoroborate anion was back-extracted from the chloroform layer with nitric acid for determination by ICP-QMS. Effective parameters for the complex formation and its extraction, such as volume of extractant/disperser solvent, extraction time and concentration of the surfactant have been optimized. Under optimum conditions, an average preconcentration factor of 18 was obtained for 8 mL of water sample for determination by ICP-QMS. The calibration graph was linear in the range of 1–50 μg L−1 for boron, with a limit of detection of 0.3 μg L−1, calculated based on 3 s of blank (n = 6). The precision was close to 3% R.S.D. (n = 3), when processing 8 mL aliquots of sample. The method has been applied to determine boron in bottled mineral water, groundwater, wastewater and seawater samples. The recoveries obtained for the boron spiked to 30 μg L−1 levels in these water samples were 97–102%.