Selective determination of antimony(III) and antimony(V) in liver tissue by microwave-assisted mineralization and hydride generation atomic absorption spectrometry

Antimony(III) and antimony(V) species have been selectively determined in liver tissues by optimizing the acidic conditions for the evolution of stibine using the reduction with sodium borohydride. The results show that a response for Sb(III) of 0.5 to 20 g l^–1 was selectively obtained from samples in a 1 mol l_–1 acetic acid medium. The best response for total antimony from 1 to 20 g l^–1 is obtained after sample treatment with a 0.5 mol l^–1 sulfuric acid and 10% w/v potassium iodide. Microwave digestion has been necessary to release quantitatively antimony species from sample slurries. The amount of Sb(V) was calculated from the difference between the value for total antimony and Sb(III) concentrations. A relative standard deviation from 2.9 to 3.1% and a detection limit of 0.15 and 0.10 g l^–1 for Sb(III) and total Sb has been obtained. The average accuracy exceeded 95% in all cases comparing the results obtained from recovery studies, electrothermal atomic absorption spectrometry and the analysis of certified reference materials.Dedicated to Professor Dr. Peter Brätter on the occasion of his 60th birthday     

Antimony determination and speciation by multisyringe flow injection analysis with hydride generation-atomic fluorescence detection

A new analytical procedure for determination of inorganic antimony and speciation of antimony(III) and antimony(V) is presented. For this purpose, a software-controlled time-based multisyringe flow injection system, which contains a multisyringe burette provided with a multi-port selection valve, was developed. Hydride generation-atomic fluorescence spectrometry was used as a detection technique. A 0.3% (w/v) reducing sodium tetrahydroborate solution, hydrochloric acid (2 M), an antimony solution and a pre-reducing solution of 10% (w/v) KI and 0.3% (w/v) ascorbic acid are dispensed simultaneously into a gas-liquid separation cell with further propulsion of the reaction product into the flame of an atomic fluorescence spectrometer using argon flow. A hydrogen flow was employed to support the flame.The linear range and the detection limit (3s_b/S) of the proposed technique were 0.2-5.6 μg l⁻¹ and 0.08 μg l⁻¹, respectively. A sample throughput of 18 samples per hour (corresponding to 80 injections per hour) was achieved. The relative standard deviation for 18 independent measurements was 4.6%. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of Sb(III) and Sb(V) by means of the developed technique were obtained.     

Preconcentration procedure using cloud point extraction in the presence of electrolyte for cadmium determination by flame atomic absorption spectrometry

This paper describes a micelle-mediated phase separation in the presence of electrolyte as a preconcentration method for cadmium determination by flame atomic absorption spectrometry (FAAS). Cadmium was complexed with ammonium O,O-diethyldithiophosphate (DDTP) in an acidic medium (0.32 mol l^− 1 HCl) using Triton X-114 as surfactant and quantitatively extracted into a small volume (about 20 μl) of the surfactant-rich phase after centrifugation. The chemical variables that affect the cloud point extraction, such as complexing time (0–20 min), Triton X114 concentration (0.043–0.87% w/v) and complexing agent concentration (0.01–0.1 mol l^− 1), were investigated. The cloud point is formed in the presence of NaCl at room temperature (25 °C), and the electrolyte concentration (0.5–5% w/v) was also investigated. Under optimized conditions, only 8 ml of sample was used in the presence of 0.043% w/v Triton X-114 and 1% (w/v) NaCl. This method permitted limits of detection and quantification of 0.9 μg l^− 1 and 2.9 μg l^− 1 Cd, respectively, and a linear calibration range from 3 to 400 μg l^− 1 Cd. The proposed method was applied to Cd determination in physiological solutions (containing 0.9% (w/v) of NaCl), mineral water, lake water and cigarette samples (tobacco).     

Determination of As(III) and As(V) in soils using sequential extraction combined with flow injection hydride generation atomic fluorescence detection

An analytical procedure for determination of As(III) and As(V) in soils using sequential extraction combined with flow injection (FI) hydride generation atomic fluorescence spectrometry (HG-AFS) was presented. The soils were sequentially extracted by water, 0.6 mol l⁻¹ KH₂PO₄ solution, 1% (v/v) HCl solution and 1% (w/v) NaOH solution. The arsenite (As(III)) in extract was analyzed by HG-AFS in the medium of 0.1 mol l⁻¹ citric acid solution, then the total arsenic in extract was determined by HG-AFS using on-line reduction of arsenate with l-cysteine. The concentration of arsenate (As(V)) was calculated by the difference. The optimum conditions of extraction and determination were studied in detail. The detection limit (3σ) for As(III) and As(V) were 0.11 and 0.07 μg l⁻¹, respectively. The relative standard deviation (R.S.D.) was 1.43% (n=11) at the 10 μg l⁻¹ As level. The method was applied in the determination of As(III) and As(V) of real soils and the recoveries of As(III) and As(V) were in the range of 89.3-118 and 80.4-111%, respectively.     

Determination of lead by hydride generation inductively coupled plasma mass spectrometry (HG-ICP-MS): On-line generation of plumbane using potassium hexacyanomanganate(III)

A hydride generation (HG) procedure has been described for determination of Pb by ICP-MS using potassium hexacyanomanganate(III), K₃Mn(CN)₆, as an additive to facilitate the generation of plumbane (PbH₄). Potassium hexacyanomanganate(III) was prepared in acidic medium as it was unstable in water. The stability of hexacyanomanganate(III) was examined in dilute solutions of HCl, HNO₃ and H₂SO₄. The solutions prepared in 1% v/v H₂SO₄ were found to be stable for over a period of 24 h. The least suitable medium was 1% v/v HNO₃. For generation of plumbane, acidic hexacyanomanganate(III) and sample solutions were mixed on-line along a 5-cm long tygon tubing (1.14 mm i.d.) and then reacted with 2% m/v sodium borohydride (NaBH₄). A concentration of 0.5% m/v K₃Mn(CN)₆ facilitated the generation of PbH₄ remarkably. In comparison to H₂SO₄, HCl provided broader working range for which optimum concentration was 1% v/v. No significant interferences were noted from transition metals and hydride forming elements, up to 0.5 μg mL⁻¹ levels, except Cu which depressed the signals severely. The depressive effects in the presence of 0.1 μg mL⁻¹ Cu were alleviated by increasing the concentration of K₃Mn(CN)₆ to 2% m/v. Under these conditions, the sensitivity was enhanced by a factor of at least 42 to 48. The detection limit (3 s) was 0.008 μg L⁻¹ for ²⁰⁸Pb isotope. Average signal-to-noise ratio (S/N) ranged between 18 and 20 for 1.0 μg mL⁻¹ Pb solution. The accuracy of the method was verified by analysis of several certified reference materials, including Nearshore seawater (CASS-4), Bone ash (SRM 1400), and Mussel tissue (SRM 2976). The procedure was also successfully applied to the determination of Pb in coastal seawater samples by ICP-MS.     

Fermentation performance characteristics of a prehydrolyzate-adapted xylose-fermenting recombinant Zymomonas in batch and continuous fermentations

Long-term (149 d) continuous fermentation was used to adapt a xylose-fermenting recombinant Zymomonas mobilis, strain 39676:pZB 4L, to conditioned (overlimed) dilute-acid yellow poplar hemicellulose hydrolyzate (“prehydrolyzate”). An “adapted” variant was isolated from a chemostat operating at a dilution rate of 0.03/h with a 50% (v/v) prehydrolyzate, corn steep liquor, and sugar-supplemented medium, at pH 5.75. The level of xylose and glucose in the medium was kept constant at 4% (w/v) and 0.8% (w/v), respectively. These sugar concentrations reflect the composition of the undiluted hardwood prehydrolyzate. The level of conditioned hardwood prehydrolyzate added to the medium was increased in 5% increments startingata level of 10%. At the upper level of 50% prehydrolyzate, the acetic-acid concentration was about 0.75% (w/v). The adapted variant exhibited improved xylose-fermentation performance in a pure-sugar, synthetic hardwood prehydrolyzate medium containing 4% xylose (w/v), 0.8% (w/v) glucose, and acetic acid in the range 0.4–1.0% (w/v). The ethanol yield was 0.48–0.50 g/g; equivalent to a sugar-to-ethanol conversion efficiency of 94–96% of theoretical maximum. The maximum growth yield and maintenance energy coefficients were 0.033 g dry cell mass (DCM)/g sugars and 0.41 g sugars/g DCM/h, respectively. The results confirm that long-term continuous adaptation is a useful technique for effecting strain improvement with respect to the fermentation of recalcitrant feedstocks.     

Total and inorganic mercury determination in fish tissue by flow injection cold vapour atomic fluorescence spectrometry

A simple and reliable method for Hg determination in fish samples has been developed. Lyophilised fish tissue samples were extracted in a 25% (w/v) tetramethylammonium hydroxide (TMAH) solution; the extracts were then analysed by FI-CVAFS. This method can be used to determine total and inorganic Hg, using the same FI manifold. For total Hg determination, a 0.1% (w/v) KMnO₄ solution was added to the FI manifold at the sample zone, followed by the addition of a 0.5% (w/v) SnCl₂ solution, whereas inorganic Hg was determined by adding a 0.1% (w/v) L-cysteine solution followed by a 1.0% (w/v) SnCl₂ solution to the FI system. The organic fraction was determined as the difference between total and inorganic Hg. Sample preparation, reagent consumption and parameters that can influence the FI-CVAFS performance were also evaluated. The limit of detection for this method is 3.7 ng g^?1 for total Hg and 4.3 ng g^?1 for inorganic Hg. The relative standard deviation for a 1.0 µg L^?1 CH₃Hg standard solution (n = 20) was 1.1%, and 1.3% for a 1.0 µg L^–1 Hg²⁺ standard solution (n = 20). Accuracy was assessed by the analysis of Certified Reference Material (dogfish: DORM-2, NRCC). Recoveries of 99.1% for total Hg and 93.9% inorganic Hg were obtained. Mercury losses were not observed when sample solutions were re-analysed after a seven day period of storage at 4°C.     

Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethylenebis(triphenylphosphoniu) cation

Cobalt (0–10 μg) may be determined spectrophotometrically at 625 nm after flow-injection extraction into chloroform of the ion associate ethylenebis(triphenylphosphonium) tetrathiocyanatocobaltate(II). The carrier stream contained 10% (w/v) ammonium fluoride and the reagent stream contained 0.5% (w/v) ethylenebis (triphenylphosphonium) bromide and 5% (w/v) ammonium thiocyanate. The injection rate was 20 h^?1. The calibration graph is linear up to 20 μg ml^?1 and detection limit is 0.23 μg ml^?1 cobalt, based on injection volumes of 500 μl. The system has been applied to the determination of cobalt in a range of tool steels.     

Application of solvent extraction and synchronous spectrofluorimetry to the determination of the formation constant for a 1:1 complex of carbazole withβ-cyclodextrin in water-dimethyl sulfoxide medium

Extraction of carbazole in heptane was performed at 25±1°C with an aqueous dimethyl sulfoxide (DMSO) medium containing -cyclodextrin (CD) at consecutive concentrations in the range of 0–10 mM. The fluorescence intensity of carbazole remaining in the heptane phase was measured by synchronous scanning fluorimetry. The apparent formation constant (K _f) for a 1:1 carbazole: CD inclusion complex in water-DMSO medium was determined by using a linear plot of the distribution ratio calculated from the fluorescence intensities vs. the -CD concentration. The values thus obtained ranged from 477 M^–1 in a 10% v/v DMSO medium to 12.1 M^–1 in a 60% v/v medium. Good linear relationships were observed between logK _f and the DMSO concentration ([DMSO]), and also between logK _f and the logarithm of the distribution coefficient (K _d) for carbazole. The formation constant in 100% water was estimated to be approximately 1.0×10³ M^–1 on the basis of the logK _f vs. [DMSO] and the logK _f vs. logK _d correlations.     

Determination of toxic and non-toxic arsenic species in urine by microwave assisted mineralization and hydride generation atomic absorption spectrometry

Flow injection — microwave oven — hydride generation — atomic absorption spectroscopy (FI-MO-HG-AAS) has been optimized for the determination of the total and toxic arsenic in urine with and without persulfate, respectively. With microwave oven assisted digestion of urine with 5% (w/v) K₂S₂O₈ and 5% (w/v) NaOH all arsenicals completely can be converted to arsenate, which is determined by HG-AAS to give the total concentration of the six species present in urine. The detection limits of 4–6 g l^–1, the relative standard deviation of 3–7% and the high sample throughput make the methods suitable for rapid routine on-line determination. Application of the proposed procedures to the analysis of urine from people on a diet rich in seafood revealed a significant increase in total urinary arsenic due to the rapid excretion of organoarsenicals. Efficient decomposition and quantitative recovery of all arsenic species in spiked urine is achieved by using 5% K₂S₂O₈ in 5% NaOH at 4.6 ml min^–1, microwave power of 700 W and a 1.5 m coil.     

Determination of lead in complex sample matrices by atomic fluorescence spectrometry: optimisation of online hydride generation

Lead hydride or plumbane (PbH₄) generation was optimised by exploiting a simple flow-injection method coupled to atomic fluorescence spectrometry (HG-AFS), and allowing ultra-trace lead determination. Plumbane was generated through two methods: (1) 5% (v/v) H₂O₂ was employed as oxidant with 1.5% (m/v) KBH₄ as a reducing agent and 1.5% (v/v) HCl solution; (2) with 1.5% (m/v) K₃[Fe(CN)₆] as an oxidant/sensitiser, 1% (m/v) KBH₄ as a reducing agent and 1.5% (v/v) HCl. Variables such as reagent concentrations, flow rates and sample and reagent volumes were tested and critically compared. The best results were obtained with potassium ferricyanide K₃[Fe(CN)₆], achieving a detection limit of 0.03 μg Pb L^?1 and a relative standard deviation (RSD) of 1.1%. The selected method was validated by analysis of certified reference materials such as SRM-2976 (mussel tissue) and BCR-610 (groundwater), with good agreement with the certified values. The developed methodology was successfully applied to different environmental sample matrices, such as rain water, tap water, ground water, spring water and drinking water, and biological samples, i.e., human blood, plasma and serum.     

Determination of sulfur in coal and ash slurry by high-resolution continuum source electrothermal molecular absorption spectrometry

We propose a procedure for the determination of sulfur in coal slurries by high resolution continuum source electrothermal molecular absorption spectrometry. The slurry, whose concentration is 1 mg mL^− 1, was prepared by mixing 50 mg of the sample with 5% v/v nitric acid and 0.04% m/v Triton X-100 and was homogenized manually. It sustained good stability. The determination was performed via CS molecular absorption at 257.592 nm, and the optimized vaporization temperature was 2500 °C. The accuracy of the method was ensured by analysis of certified reference materials SRM 1632b (trace elements in coal) and SRM 1633b (coal fly ash) from the National Institute of Standards and Technology, using external calibration with aqueous standards prepared in the same medium and used as slurry. We achieved good agreement with the certified reference materials within 95% confidence interval, LOD of 0.01% w/w, and RSD of 6%, which confirms the potential of the proposed method.     

Determination of tin in marine materials by using hydride generation-high resolution inductively coulped plasma mass spectrometry

A hydride generation system combined with high-resolution inductively coulped plasma mass spectrometry was used to determine tin in marine materials. The optimization conditions for determination of tin in this system are 0.015 M of sulfuric acid solution as medium, 0.2% (w/v) of sodium tetrahydroborate(III) in 0.015 M of sodium hydroxide solution as a reductant and argon as the carrier gas at a flow rate of 1.1 l min(-1). In order to remove the interferences from transition element ions, a strongly basic anion exchanger was used in this method. Tin was converted to its chlorostannate with 2 M hydrochloric acid followed by passing to an anion exchanger. The tin absorbed on the column was then eluted with 1 M nitric acid. Under the optimized conditions, the detection limit of the method was 12 ng l(-1) without using the anion column as preconcentration method. The results obtained using this method were in good agreement with the certified values of marine standard reference materials. The recoveries for the method when applied to determine trace tin in river water were 95-115%.     

Liquid-chromatographic determination of sulfadimidine in milk and eggs

A method for the determination/identification of residual sulfadimidine (SDD) in milk and eggs by high-performance liquid chromatography (HPLC) with a photo-diode array detector was developed. The sample preparation was performed by shaking with a mixture of 20% (w/v) trichloroacetic acid-methanol (4:1, v/v) followed by ultra-filtration using Molcut II^®. A LiChrospher^® 100 RP-8 (e) column and a mobile phase of 4% (v/v) acetic acid solution-acetonitrile (6:4, v/v) were used. The average recoveries from spiked SDD samples were 80.8–88.0% with coefficients of variation of 2.8–5.5%. The limits of detection in milk and eggs were 0.01 μg/mL and 0.01 μg/g, respectively. The total time required for the analysis of one sample was less than 20 min.     

Determination of arsenic in biological fluids by electrothermal atomic absorption spectrometry

A procedure for the determination of the total content of arsenic in urine, serum and blood by electrothermal atomic absorption spectrometry (ETAAS) is described. Zeeman correction is used to compensate the high background signals. The samples are diluted (1 + 1 for urine and 1 + 3 for both serum and blood samples) in a medium containing 0.1% w/v Triton X-100 before being introduced directly into the furnace. A solution containing 15% w/v hydrogen peroxide, 0.65% w/v nitric acid and 0.5% w/v nickel is also introduced into the atomizer by means of a separate injection. Calibration is carried out against aqueous standards for blood and serum samples and using the standard additions method for urine samples. The detection limit is 20 pg (2 ng ml-1). The reliability of the procedure is checked by analyzing three certified reference materials and by recovery studies.     

Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix

Nickel(II)-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing neutral carrier dibenzo-18-crown-6 as electroactive material, sodium tetraphenylborate (NaTPB) as an anion excluder and tris-(2-ethylhexyl) phosphate (TEHP) as plasticizing solvent mediator. The membrane having the composition of crown ether:NaTPB:TEHP:PVC in the ratio 10:1:200:200 (w/w) exhibits best results with linear potential response in the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M and a Nernstian slope of 29.5 mV/decade of activity between 2.6 and 6.8. The sensor exhibits a fast response time of <25 s, is inert towards non-aqueous medium up to 15% (v/v) and was used over a period of 4 months with good reproducibility. It is selective over a number of mono-, bi- and trivalent cations. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Ni²⁺ against EDTA and also for the estimation of Ni²⁺ in some Indian brand chocolates.     

Liquid-chromatographic determination of sulfadimidine in milk and eggs

A method for the determination/identification of residual sulfadimidine (SDD) in milk and eggs by high-performance liquid chromatography (HPLC) with a photo-diode array detector was developed. The sample preparation was performed by shaking with a mixture of 20% (w/v) trichloroacetic acid-methanol (4:1, v/v) followed by ultra-filtration using Molcut II^?. A LiChrospher^? 100 RP-8 (e) column and a mobile phase of 4% (v/v) acetic acid solution-acetonitrile (6:4, v/v) were used. The average recoveries from spiked SDD samples were 80.8–88.0% with coefficients of variation of 2.8–5.5%. The limits of detection in milk and eggs were 0.01 μg/mL and 0.01 μg/g, respectively. The total time required for the analysis of one sample was less than 20 min. Received: 7 October 1998 / Revised: 29 December 1998 / Accepted: 30 December 1998     

Antimony speciation in soils: improving the detection limits using post-column pre-reduction hydride generation atomic fluorescence spectroscopy (HPLC/pre-reduction/HG-AFS)

HG-AFS is highly sensitive and low cost detection system and its use for antimony chemical speciation coupled to HPLC is gaining popularity. However speciation analysis in soils is strongly hampered because the most efficient extractant reported in the literature (oxalic acid) strongly inhibits the generation of SbH₃ by Sb(V), the major species in this kind of matrix, severely affecting its detection limits. The purpose of this research is to reduce the detection limit of Sb(V), by using a post column on-line reduction system with l-cysteine reagent (HPLC/pre-reduction/HG-AFS). The system was optimized by experimental design, optimum conditions found were 2% (w/v) and 10 °C temperature coil. Detection limits of Sb(V) and Sb(III) in oxalic acid (0.25 mol L⁻¹) were improved from 0.3 and 0.1 μg L⁻¹ to 0.07 and 0.07 μg L⁻¹, respectively. The methodology developed was applied to Chilean soils, where Sb(V) was the predominant species.     

Flow-injection extraction spectrophotometric determination of bismuth as tetraiodobismuthate(III) with the tetramethylenebis(triphenylphosphonium) cation

Bismuth can be determined spectrophotometrically at 495 nm after its extraction as tetramethylenebis(triphenylphosphonium) tetraiodobismuthate(III) into dichloromethane. The carrier stream is 2 M sulphuric acid and the reagent stream contains 2% (w/v) potassium iodine and 0.4% (w/v) tetramethylenebis(triphenylphosphonium) bromide. The injection rate is 20 h^-1. The calibration graph is linear up to 20 μ ml^-1 bismuth and the detection limit is 0.24 μ ml^-1 bismuth, based on injection volumes of 250μl. The system has been applied to determination of bismuth in pharmaceutical samples.     

Determination of ultra trace arsenic species in water samples by hydride generation atomic absorption spectrometry after cloud point extraction

Cloud point extraction (CPE) methodology has successfully been employed for the preconcentration of ultra-trace arsenic species in aqueous samples prior to hydride generation atomic absorption spectrometry (HGAAS). As(III) has formed an ion-pairing complex with Pyronine B in presence of sodium dodecyl sulfate (SDS) at pH 10.0 and extracted into the non-ionic surfactant, polyethylene glycol tert-octylphenyl ether (Triton X-114). After phase separation, the surfactant-rich phase was diluted with 2 mL of 1 M HCl and 0.5 mL of 3.0% (w/v) Antifoam A. Under the optimized conditions, a preconcentration factor of 60 and a detection limit of 0.008 μg L⁻¹ with a correlation coefficient of 0.9918 was obtained with a calibration curve in the range of 0.03–4.00 μg L⁻¹. The proposed preconcentration procedure was successfully applied to the determination of As(III) ions in certified standard water samples (TMDA-53.3 and NIST 1643e, a low level fortified standard for trace elements) and some real samples including natural drinking water and tap water samples.