Sunil Jai Kumar

An acid induced mixed-micelle mediated cloud point extraction for the separation and pre-concentration of platinum from road dust and determination by inductively coupled plasma mass spectrometry

An acid induced mixed-micelle mediated cloud point extraction procedure is developed for the separation and pre-concentration of platinum from digested road dust matrices. The mixed-micelle is formed from the micelle–micelle interaction of cetyltrimethylammonium bromide (CTAB) (cationic) and Triton X-100 (nonionic) surfactants. Nitric acid induces the clouding as well as phase separation in these mixed-micelles. In the presence of mixed acids (HCl and HNO3), platinum forms stable and extractable anionic species compared to palladium and rhodium, which provides the quantitative separation of platinum, from palladium and rhodium, by forming the hydrophobic ion-associated complex with quaternary ammonium head groups of mixed-micelles. This hydrophobic complex is subsequently pre-concentrated from a bulk aqueous phase into a small mixed-micelles rich phase, avoiding the addition of an external chelating agent. The potential oxide interference of Hf is eliminated effectively up to 1 mg L−1 level, enabling interference free determination of 195Pt using inductively coupled plasma mass spectrometry (ICP-MS). The parameters affecting the extraction process are optimized. Under the optimized conditions, the pre-concentration factor and detection limit are 13 and 10 pg g−1, respectively. The recoveries are in the range 92–99% at 100–200 pg mL−1 with relative standard deviation 2.0–3.5%. The accuracy of the procedure is evaluated by platinum determination in certified reference materials such as CCRMP PTC-1a Copper-Nickel sulfide concentrate and BCR 723 Road dust and the results agreed with the certified values with 95% confidence level, as well as being applied to road dust samples.

Determination of thallium at trace levels by electrolyte cathode discharge atomic emission spectrometry with improved sensitivity

An analytical method using electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES) has been described for the trace determination of thallium after improving its sensitivity. Parameters influencing the sensitivity of thallium are investigated at its emission wavelength of 377.572 nm. Maximum enhancement of sensitivity is obtained with the combination of a surfactant (Triton X-114) and potassium iodide. Sensitivity of thallium is improved 12 times with the use of an optimised composition of 3.5% v/v Triton X-114 and 0.2% w/v of KI. Under the optimized conditions, the achieved detection limit is 1 μg L−1 which is 100 times better compared to the detection limit obtained without addition of the surfactant and KI. The precision of the method is 2% for thallium of 500 μg L−1 concentration. The accuracy of the proposed method has been validated by analyzing a NIST 1633b coal fly ash certified reference material and a IAEA 394 coal fly ash material. On comparison, the ELCAD-AES results are found to be in agreement with the certified values and the results obtained by high resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). The detection limit of thallium for coal fly ash has been found to be 134 ng g−1. Determinations of spiked thallium at trace levels in ground water samples are carried out by ELCAD-AES and HR-CS-AAS and the results are in agreement with each other.

Determination of Cd, Pb, Cu, Ni and Mn in effluents and natural waters by a novel salt induced mixed-micelle cloud point extraction using ETAAS

A novel salt induced low temperature mixed-micelle cloud point extraction procedure is developed for simultaneous separation and pre-concentration of Cd, Pb, Cu, Mn and Ni from industrial effluents and natural water matrices. Electrothermal atomic absorption spectrometry has been used for their determination. The mixed-micelles are formed by micelle–micelle interaction of Triton X-114 and sodium dodecyl sulfate (SDS) micelles. These mixed aggregates have a strong hydrophobic core, due to strong packing of both hydrophobic cores of Triton X-114 and SDS micelles, which is further enhanced by the addition of an electrolyte. These enhanced hydrophobic solubilising sites are used for efficient extraction of ammonium pyrrolidine dithiocarbamate (APDC) metal chelates at temperatures of 25–5 °C. This low temperature extraction avoids the thermal decomposition of these thermally labile complexes. The parameters affecting the extraction procedures are optimized. Under the optimized conditions, a pre-concentration factor of 10 was obtained with limits of detection of 5, 80, 30, 50 and 10 pg mL−1, respectively for Cd, Pb, Cu, Ni and Mn. The recoveries are in the range of 95–102% with 2–5% relative standard deviation. The accuracy of the procedure is evaluated by analyzing various certified reference materials such as BCR-713 final effluent, BCR-715 industrial effluent, BCR-609 ground water and NIST-1640a natural water matrices and also applied to real samples.

Microwave assisted aqua regia extraction of thallium from sediment and coal fly ash samples and interference free determination by continuum source ETAAS after cloud point extraction.

A simple cloud point extraction method is described for the separation and pre-concentration of thallium from the microwave assisted aqua regia extracts of sediment and coal fly ash samples. The method is based on the formation of extractable species of thallium and its interaction with hydrophobic solubilizing sites of Triton X-114 micelles in the presence of aqua regia and electrolyte NaCl. These interactions of micelles are used for extraction of thallium from a bulk aqueous phase into a small micelles-rich phase. The potential chloride interferences are eliminated effectively, which enabled interference free determination of thallium from aqua regia extracts using continuum source ETAAS. The parameters affecting the extraction process are optimized. Under the optimized conditions, pre-concentration factor and limit of detection are 40 and 0.2 ng g(-1), respectively. The recoveries are in the range of 95-102%. A characteristic mass, 13 pg was obtained. The accuracy of the method is verified by analyzing certified reference materials such as NIST 1633b coal fly ash, NIST 1944 marine sediment and GBW 07312 stream sediments. The results obtained are in good agreement with the certified values and method is also applied to real samples.

A novel non-chromatographic strategy for the sequential/simultaneous extraction and analysis of chromium species by electrothermal atomic absorption spectrometry in effluents and different water sources

A novel surfactant assisted dispersive liquid–liquid microextraction based on the solidification of floating organic drop procedure is developed for the sequential and simultaneous pre-concentration of Cr(III) and Cr(VI) from tap, river, ground and wastewaters. The sequential extraction is based on the selective formation of extractable complexes of Cr(III) with the reactive head group solubilising sites of the dispersible dodecyl benzene sulfonate surfactant, in the presence of Cr(VI). The extracting, 1-undecanol pre-concentrates the formed extractable Cr(III) from the bulk aqueous solution and solidifies it on lowering the temperature. Cr(VI) present in the aqueous solution is subjected to a similar extraction procedure after the addition of diphenylcarbazide. In the simultaneous extraction, both the species are extracted by adapting a similar extraction procedure after the addition of diphenylcarbazide and surfactant to fresh aliquots, to determine the total chromium content. The chromium concentrations in the 1-undecanol phases are determined using continuum source ETAAS (Electrothermal Atomic Absorption Spectrometry). The parameters affecting the process are optimized. Under the optimized conditions, the pre-concentration factors and limits of detections for Cr(III) and Cr(VI) in sequence and total Cr in simultaneous extractions are 25, 50 and 40; and 3, 1 and 4 pg mL−1, respectively. The recoveries are in the range of 94–99% at 50–400 pg mL−1 for Cr(III) and Cr(VI). The accuracy of the procedure is validated by comparing the sum of the concentrations of each individual species obtained from the sequential extraction with total chromium obtained in the simultaneous extraction procedure applied to certified reference materials such as the BCR 713 effluent, BCR 714 influent and NIST 1643c water and water samples.

A sensitive sequential non-chromatographic speciation analysis of chromium in natural/wastewaters by inductively coupled plasma optical emission spectrometry

A highly sensitive and novel sequential non-chromatographic speciation procedure has been developed for selective pre-concentration and separation of Cr(III) and Cr(VI) from natural and wastewaters. In this procedure, Triton X-114 micelle and cetylpyridinium bromide-Triton X-114 mixed-micelle are used sequentially for the extraction of hydrophobic Cr(III)-trifluoropentanedione and hydrophilic Cr(VI), respectively. Inductively couple plasma optical emission spectrometry (ICP-OES) is used for its determination. The parameters affecting the extraction process are optimized. Under the optimized conditions, the pre-concentration factors obtained are 50 and 15 while limits of detection (LOD) are 0.02 and 0.05 ng mL−1 for Cr(III) and Cr(VI), respectively. These LODs are better than those of IC-ICP-MS and comparable to those of IC-ICP-DRC-MS methods. The recoveries are in the range of 95 to 99% at 10 to 40 ng mL−1 with relative standard deviation of 2–4%. The accuracy of the procedure is validated by comparing the sum of the concentrations of each individual chromium species obtained from sequential extraction with total chromium in BCR certified reference materials such as Effluent-713, Influent-714 and Industrial effluent-715. The method was then applied to various water samples collected locally.

A sensitive speciation analysis of chromium in natural and industrial effluents by electrothermal atomic absorption spectrometry after a novel ligandless mixed-micelle dispersive liquid–liquid microextraction

A simple, fast and sensitive method was developed for determining Cr(III), Cr(VI) and total Cr separately in natural river and lake waters and tannery effluent samples. In this method, a new strategy of micelle and mixed-micelles was introduced in dispersive liquid–liquid microextraction (M-MM-DLLME) for sequential and simultaneous separation and pre-concentration of Cr(VI) and Cr(III) at a sampling site. Cationic Aliquat-336 and anionic dioctylsulfosuccinate (DOSS) surfactant aggregates were used as dispersive and chelating solvents, respectively, for extracting Cr(VI) and Cr(III). In sequential speciation, the hydrophilic HCrO4−, first reacts electively with the cationic head group solubilising sites of Aliquat-336 micelles through electrostatic interaction and form extractable charge neutral Cr(VI)-Aliquat-336 at room temperature in the presence of Cr(III). The extracting trichloroethylene pre-concentrates this extractable species from bulk aqueous phase and leaves the unreacted cationic Cr(H2O)63+ in the supernatant. This supernatant is subjected to a similar extraction procedure after adding an anionic DOSS surfactant. In the simultaneous speciation, both the species were extracted by adapting a similar extraction procedure after adding DOSS and Aliquat-336 mixed-micelles to fresh aliquots to determine total Cr, avoiding the addition of a chelating agent and oxidation/reduction steps. The surfactant stabilized chromium species in the trichloroethylene phases were transferred to a laboratory for quantification using electrothermal atomic absorption spectrometry (ETAAS) the parameters affecting the process are evaluated and optimized. Under the optimized conditions, the pre-concentration factors and limits of detection for Cr(III) and Cr(VI) in sequential and total Cr in simultaneous extractions were 100, 90 and 83 and 0.5, 0.6 and 0.7 pg mL−1, respectively. The accuracy of the procedure was verified by comparing the sum of the concentrations of each individual species obtained from the sequential extraction with total Cr obtained in the simultaneous extraction procedures and applied to certified reference materials such as BCR 714 industrial influent, BCR 715 industrial effluent and NIST 1640 natural water. This method was applied to on-site extraction of individual and total Cr from natural waters and effluents.

Sequential extraction of platinum, cisplatin and carboplatin from environmental samples and pre-concentration/separation using vesicular coacervative extraction and determination by continuum source ETAAS

A sequential extraction procedure is developed for the separation of trace levels of hexachloroplatinate, cisplatin and carboplatin from soil, which are then, pre-concentrated using a vesicular coacervative cloud point extraction method prior to their determination as platinum by continuum source ETAAS. Sequential extraction of carboplatin, cisplatin and hexachloroplatinate from a specific red soil is achieved by using the 20% HCl, aqua regia at room temperature and by combination of aqua regia and HF with microwave digestion, respectively. The pre-concentration of these species from the extracted solutions is based on the formation of extractable hydrophobic complexes of PtCl₆(2-) anionic species with free cationic head groups solubilizing sites of the Triton X-114 co-surfactant stabilized TOMAC (tri-octyl methyl ammonium chloride) vesicles through electrostatic attraction. This process separates the platinum from bulk aqueous solution into a small vesicular rich phase. The parameters affecting the extraction procedures are optimized. Under the optimized conditions, the achieved pre-concentration factor is 20 and detection limit is 0.5 ng g(-1) for soil and 0.02 ng mL(-1) for water samples. The spiked recoveries of hexachloroplatinate, cisplatin and carboplatin in water and soil extracts in the vesicular coacervative extraction are in the range of 96-102% at 0.5-1 ng mL(-1) with relative standard deviation of 1-3%. The accuracy of the method for platinum determination is evaluated by analyzing CCRMP PTC-1a copper-nickel sulfide concentrate and BCR 723 road dust certified reference materials and the obtained results agreed with the certified values with 95% confidence level of student t-test. The results were also compared to mixed-micelle (MM)-CPE method reported in the literature.

Determination of cadmium in Zircaloys by electrolyte cathode discharge atomic emission spectrometry (ELCAD-AES)

An electrolyte cathode discharge atomic emission spectrometric (ELCAD-AES) method has been reported for the determination of cadmium in Zircaloys. Formic and acetic acids are examined to improve the sensitivity of ELCAD-AES for cadmium determination. The sensitivity of ELCAD-AES is improved 2-fold with 20% (v/v) formic acid. With 20% (v/v) formic acid, the improved detection limit of ELCAD-AES for cadmium is found to be 2 ng mL−1. A previously reported matrix separation procedure using ammonium pyrrolidine dithiocarbamate (APDC) and methylisobutylketone (MIBK) for the extraction of Cd from Zirconium matrices has been optimised for ELCAD-AES analysis of cadmium. This procedure is found to be useful for the quantitative determination of cadmium in Zircaloys by ELCAD-AES. The precision expressed as a percentage relative standard deviation of the signals of multiple analyses (N = 5) of ELCAD-AES method using the above matrix separation procedure has been found to be 10–15% for trace Cd. This ELCAD-AES method is validated with the certified values of Zircaloy CRM and the glow discharge quadrupole mass spectrometry (GD-QMS) values of Zircaloy samples.

Determination of Cd, Co, Cu, Fe and Ni at parts per billion level in high-purity gallium by graphite furnace atomic absorption spectrometry (GFAAS)

SummaryThe determination of Cd, Co, Cu, Fe and Ni in 6N gallium by GFAAS is reported. The analytes are extracted as pyrrolidine dithiocarbamates into methyl-iso-butyl-ketone (MIBK) in the presence of tartrate. The conditions of extraction, quantity of reagents required and the matrix interference aspects are discussed. The method offers one-step matrix removal and preconcentration, leading to low experimental blanks.