Krishnan Chandrasekaran

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.

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%.

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%.

A simple and rapid microwave-assisted extraction method using polypropylene tubes for the determination of total mercury in environmental samples by flow injection chemical vapour generation inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS)

Presented here is the development of a simple, rapid and cost-effective microwave-assisted extraction (MAE) method using closed polypropylene tubes (PP) and a domestic microwave oven for the determination of total mercury in a wide variety of environmental samples (coal, coal-fly ash, sediments and sludges). Extraction of mercury was achieved using microwave energy with a mixture of HNO3–thiourea as extractant for subsequent determination by flow injection chemical vapour generation inductively coupled plasma mass spectrometry (FI-CVG-ICP-MS). Two types of reference materials certified for mercury; Coal fly ash NIST-1633b and estuarine sediment ERM-CC-580 were taken to optimize extraction parameters such as microwave power, extraction time and sample amount for the quantitative recovery of mercury. The supernatant obtained upon centrifugation was used for analysis. Quantitative recoveries of mercury were obtained using 30% HNO3–0.02% thio-urea mixture 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 5% in all the cases. The limit of detection of the proposed method in conjunction with FI-CVG-ICP-MS was obtained to be 0.9 ng g−1. A closed-microwave extraction procedure based on US EPA method (3051A) was used for the determination of mercury for comparison purposes. The optimized MAE procedure was successfully applied to real samples.

A novel Cu–BSA nanocomposite based vapour generation approach for the rapid determination of mercury in aqueous media by cold vapour atomic absorption spectrometry and on-line flow injection inductively coupled plasma mass spectrometry

The present study reports, for the first time, novel Copper–Bovine Serum Albumin nanocomposites (Cu–BSA NCs) based vapor generation as a simple, rapid and reliable approach for the sensitive determination of mercury in water. Copper nanoparticles in the form of Cu–BSA NCs acted as reductant to convert mercury ions to elemental mercury (Hg0) which was subsequently quantified using cold vapour atomic absorption spectrometry (CVAAS) and on-line flow injection inductively coupled plasma mass spectrometry (FI-ICPMS). The basic experimental parameters such as reaction time, amount of copper nanoparticles, pH and temperature of sample solution related to chemical vapour generation (CVG), have been optimized for both inorganic mercury (iHg) and methyl mercury (MeHg) species using CVAAS in batch mode. These studies indicate that the reduction process is very rapid (<20 s) when the pH and temperature of the sample solution is maintained at ≥4.0 and ∼90 °C, respectively. After optimizing the conditions by CVAAS, further studies were performed with on-line FI-ICPMS. The recoveries of mercury species were found to be in the range of 97–104%. The absolute limits of detection of the developed method in conjunction with FI-ICPMS were 2.8 pg and 4.1 pg for iHg and MeHg, respectively. Interference of concomitant ions and possible mechanism of the Cu–BSA NCs induced vapor generation of mercury have been discussed in detail. The proposed CVG method was applied to the analysis of total mercury in various natural water samples.

Dispersive liquid–liquid microextraction for simultaneous preconcentration of platinum group elements (Pd, Os, Ir, and Pt) and selected transition elements (Ag, Cd, Ta, and Re) at parts per trillion levels in water and their determination by inductively coupled plasma-mass spectrometry

A simple and environmentally friendly procedure for the simultaneous determination of platinum group elements (Pd, Os, Ir and Pt) and selected transition elements (Ag, Cd, Ta and Re) of industrial importance in water has been developed. The elements were extracted as their chloro and/or fluoro (anionic) complexes by dispersive liquid–liquid microextraction (DLLME) and determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The anionic complexes formed in the presence of 1 mol L−1 HCl and 0.5 mol L−1 F− were extracted into chloroform in the presence of Aliquat® 336 (tricaprylmethylammonium chloride) at room temperature. Analytes were back extracted from the chloroform layer with a mixture of perchloric acid and nitric acid for subsequent determination by ICP-MS. Effective parameters for the complex formation and its extraction, such as the concentration of HCl and KF, volume of the extractant/disperser solvent, extraction time and concentration of the surfactant, have been optimized. The effect of the interfering ions on the recovery of analytes was also investigated. Under optimum conditions, the preconcentration factors of the above elements ranged from 27–75 for 35 mL of water samples for determination by ICP-QMS. The calibration graphs were linear in the range of 10–500 ng L−1 for the 8 elements, with limits of detection ranging from 0.04–0.3 ng L−1. The precision was better than 5% R.S.D. (n = 6). The proposed DLLME procedure was applied to the analysis of lake water contaminated with industrial effluents and hospital wastes, collected from four different locations of a popular lake situated in the middle of the Hyderabad city of Telangana, India. The percentage recovery, spiked to 10 and 20 ng L−1, was in the range from 92–101%. Subsequently, the method was validated by comparing the results obtained by HR-ICPMS with those obtained by spiked recovery using pure standards and a certified precious metal standard (CMS-2).

Development of on-line UV-induced volatile species generation for selenium speciation [Se(IV) and SeCN−] by ion chromatography-inductively coupled plasma mass spectrometry in petroleum refinery wastewater

An on-line UV-induced vapor generation method has been developed that allows simultaneous conversion of selenocyanate [SeCN−] and [Se(IV)] to volatile species for their subsequent determination by IC-ICPMS in petroleum refinery wastewater with improved detection limits. The species present in the sample were separated on an anion-exchange column using a step gradient with NaOH as the eluent, and were subsequently converted to their volatile forms by UV irradiation in the presence of a mixture of HCOOH–HNO3 followed by quantitative determination using an ICP-MS. Employing a 200 μL sample injection loop, the species separation was achieved within 7 min and with the best detection limits achieved at 0.01 μg L−1 and 0.06 μg L−1 for SeCN− and Se(IV) respectively while the reproducibilities achieved for retention times and peak areas in the chromatograms were better than 1.3% and 5.0% respectively. The method was successfully employed to study the quantitative speciation of selenium in three petroleum refinery wastewaters with accuracy of the results obtained validated by two independent methods. Further validation was carried out by a standard addition method and also by analysing a certified reference material BCR-713, wastewater effluent. Quantitative recoveries (>95%) were observed for both Se(IV) and SeCN− in refinery wastewater.