Noorbasha N. Meeravali

Ultra-trace speciation analysis of thallium in environmental water samples by inductively coupled plasma mass spectrometry after a novel sequential mixed-micelle cloud point extraction

A simple and novel sequential mixed-micelle cloud point extraction procedure has been developed for ultra-trace speciation analysis of thallium in environmental water samples by inductively coupled plasma mass spectrometry (ICP-MS). A mixed micelle consisting of sodium dodecyl sulfate (SDS) and Triton X-114 is used as a chelating as well as an extracting agent. Tl(III)–DTPA (diethylenetriaminepentaacetic acid) complex in an HCl medium is extracted into a surfactant-rich phase in the presence of Tl(I). The Tl(I) in the supernatant is subjected to a similar extraction procedure after bromine oxidation. Ultrasonically assisted back-extraction is used to extract the Tl(III) species from the surfactant-rich phase into a small volume of aqueous L-cysteine. The pre-concentration factor and detection limit are 125 and 0.02 pg mL−1, respectively. The recoveries are in the range 98–103% at 10–20 pg mL−1Tl(III) with relative standard deviation (RSD) of 1–3%. The procedure is validated by comparing the sum of the concentrations of individual Tl species with total thallium concentration in certified reference materials such as Trace elements in water NIST SRM 1643c and Open ocean seawater NASS-4 and NASS-5, and also by applying it to various samples collected locally.

Interference free ultra trace determination of Pt, Pd and Au in geological and environmental samples by inductively coupled plasma quadrupole mass spectrometry after a cloud point extraction

A simple and efficient cloud point extraction procedure has been described for the pre-concentration and separation of ultra trace levels of Pt, Pd and Au simultaneously from geological and environmental samples for their determination by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). The method is based on the formation of hydrophobic complexes of Pt, Pd and Au with N,N-dihexyl-N′-benzoylthiourea in presence of an HCl medium, followed by their extraction, into a small volume of surfactant rich phase, using a non-ionic surfactant Triton X-114. The main parameters affecting the extraction process such as type and concentration of complexing agent and acids, and also the amount of Triton X-114 are optimized, which is also useful for alleviation of spectral interferences. The recoveries of analytes in the absence and presence of 4 μg mL−1 of interfering elements such as Zr, Y, Sr, Hf and Ta from road dust digest are in the range 98–105%. This indicates the effective alleviation of interfering ions. The pre-concentration factors are 100, 104 and 105, respectively, for Pt, Pd and Au with a relative standard deviation of 0.1–3.0% at 50 pg mL−1. The limits of detection for seawater and road dust samples are 0.01, 0.01 and 0.15, and 3.1, 4.4 and 44 pg g−1, respectively, for Pt, Pd and Au. The accuracy of the procedure is verified by analyzing certified reference materials such as BCR CRM 723 (road dust) for Pt and Pd, and NIST SRM 2709 (San Joaquin soil) for Au, and also by applying it to road dust samples collected locally.

Rapid slurry atomization using transverse heated electrothermal atomic absorption spectrometry for the determination of cadmium, copper, manganese and lead in biological reference materials

A rapid slurry atomization procedure for the determination of Cd, Cu, Mn and Pb in certified reference materials such as GBW 08504 Cabbage, NIST SRM 1566a Oyster Tissue and NIST SRM 1571 Orchard Leaves is described using transverse heated electrothermal atomic absorption spectrometry. The slurry was prepared in 5% HNO3 using a magnetic stirrer. No chemical modifier was used and the ashing step in the temperature programme was omitted. The atomization cycle was completed within 35–50 s. For Cd, Mn and Pb, aqueous calibration was used. For Cu, standard additions calibration was used. The Student’s t-test at the 95% confidence level was carried out on the results obtained and good agreement was observed as compared with the certified values. Stability tests on slurries in glycerol and HNO3 indicated loss of Cd in glycerol in Cabbage as well as Oyster Tissue slurries. Pb was not stable in Cabbage slurry in 0.5% HNO3 medium and Cu was not stable in Oyster Tissue slurry in glycerol. The limits of detection obtained were 0.0056, 0.066, 0.068 and 0.02 mg kg–1 for Cd, Pb, Cu and Mn, respectively. The precision of the results obtained varied between 0.2 and 2% using a rapid atomization programme.

Microwave assisted mixed-micelle cloud point extraction of Au and Tl from environmental samples without using a chelating agent prior to ICP-MS determination

A rapid microwave assisted mixed-micelle cloud point extraction procedure is developed for the pre-concentration and separation of ultra trace levels of Au and Tl simultaneously from environmental samples prior to their determination by ICP-MS. The method is based on the formation of extractable complexes of anionic species AuCl4− and TlCl32− with solubilizing cationic and hydrophobic sites of mixed-micelles, in the presence of HCl. The mixed-micelles consisting of cetyltrimethylammonium bromide (CTAB) and Triton X-114 are used for pre-concentration and extraction of formed extractable complexes of Au and Tl from a bulk aqueous phase into a small surfactant-rich phase, avoiding the addition of an external chelating agent. The phase separation is induced by microwave irradiation. The potential oxide interferences of Ta and Hf are eliminated effectively up to 2 and 5 μg mL−1 levels, respectively, enabling interference free determination of mono isotopic 197Au. The main parameters affecting the cloud point extraction process are evaluated and optimized. Under the optimized conditions, the pre-concentration factors and limits of detection are 125 and 110, and 0.12 and 0.02 pg mL−1, respectively, for Au and Tl. The recoveries of analytes are in the range of 97–103% at 10–40 pg mL−1 for Au and Tl with relative standard deviations of 0.5–2.2%. The accuracy of the procedure is validated by analyzing certified reference materials such as NIST SRM 1643c and 1643d (Trace elements in water), 2709 (San Joaquin soil) and 2711 (Montana soil), and NRCC NASS-5 (Open ocean seawater), as well as being applied to tap and seawater samples.

Zirconium–iridium coating as a permanent modifier for determination of tin in stream sediment, oyster tissue and total diet slurries by electrothermal atomic absorption spectrometry

A slurry atomization procedure has been developed for the determination of total tin in different types of environmental samples such as stream sediment, oyster tissue and total diet using a Zr–Ir permanent chemical modifier and transverse heated electrothermal atomic absorption spectrometry (THETAAS). Reference materials such as GBW07312 Stream Sediment, NIST SRM 1566a Oyster Tissue and NIST SRM 1548 Total Diet were used to validate the method. Slurries were prepared in a mixture of 1% v/v HNO3, 2% v/v HCl and 0.2% Triton X-100 solution by using magnetic stirring and ultrasonication. Addition of Triton X-100 after sonication of the slurries rather than before was found to improve the precision of measurement. With the Zr–Ir-coated tube the characteristics mass obtained was 38 ± 2 pg, which is an improvement of nearly five times compared to using an uncoated tube. The tube lifetime using aqueous standards and slurries was nearly 500 atomization cycles. The Zr–Ir permanent chemical modifier was found to effectively reduce the interference effects from chloride, phosphate and silica, as nearly 90–100% recovery was obtained in the presence of 100 μg of the matrix. In the presence of 100 μg of sulfide, aluminum nitrate and sodium silicate, 30–60% recovery was obtained, indicating the presence of matrix interferences.

Ultrasonic probe extraction of tin from botanical and biological reference materials and determination using end capped electrothermal atomic absorption spectrometry (EC-ETAAS) with zirconium–iridium permanent modifier

An ultrasonic probe extraction procedure is described for extraction of total tin in standard reference materials such as NIST SRMs 1548 total diet, 1566a oyster tissue, 2976 mussel tissue and IAEA 392 algae, and also powdered algae, onion and spinach samples. An end-capped Zr–Ir coated transverse heated tube is used for determination by electrothermal atomic absorption spectrometry, which not only enhances the sensitivity (characteristic mass 20 ± 2 pg) but also reduces the interference due to the high concentration of acids and other interfering species. The limit of detection is found to be 0.030 μg g−1. The precision expressed as relative standard deviation was in the range 2–4% within a batch and 5–10% between batches.