Tungsten Coil Electrothermal Atomic Absorption Research Articles

Application of portable tungsten coil electrothermal atomic absorption spectrometer for the determination of trace cobalt after ultrasound-assisted rapidly synergistic cloud point extraction

In this work, ultrasound-assisted rapidly synergistic cloud point extraction (UARS-CPE) was firstly established and combined with a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) for preconcentration and determination of trace cobalt. As a new instrument, the application of the portable W-coil spectrometer was expanded through the coupling with UARS-CPE, which was accomplished at room temperature rapidly by the effect of ultrasound and revulsant/synergic reagent. The instrumental conditions and influencing factors relevant to UARS-CPE efficiency, such as concentrations of surfactant and chelating agent, volume of revulsant/synergic reagent, pH, and ultrasound extraction time were studied systematically. The coupling improved the analytical performance of the portable spectrometer considerably. Under the optimal conditions, the limit of detection (LOD) for cobalt was 0.30μg/L, with sensitivity enhancement factor (EF) of 52. In order to validate its application in field analysis, some environmental water samples were field-analyzed with satisfactory results. The established method could be expanded to pre-concentrate and detect many other trace metal ions.

Combination of knotted reactor with portable tungsten coil electrothermal atomic absorption spectrometer for on-line determination of trace cadmium

In this work, flow injection (FI) on-line precipitation–dissolution in a knotted reactor (KR) was established and combined with a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) firstly for preconcentration and determination of ultra-trace cadmium. As a new instrument, the application of the portable W-coil spectrometer was expanded to carry out on-line preconcentration and detection through the coupling with a KR system. A self-assembled FI system was employed to hyphenate the KR system with W-coil ET-AAS. The instrumental conditions and influencing factors relevant to KR efficiency, such as concentration of ammonia, pH, conditions of sampling and elution were studied systematically. The coupling improved the analytical performance of the portable spectrometer considerably. Under the optimal conditions, the limit of detection (LOD) for cadmium was 0.006μg/L, with sensitivity enhancement factor (EF) of 41. The established method could be expanded and used for on-line preconcentration and detection of some other trace metal ions.

Determination of trace bismuth by using a portable spectrometer after ultrasound-assisted dispersive liquid–liquid microextraction

In this work, ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) was first coupled with a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) for trace bismuth detection. A conventional disperser solvent in DLLME was substituted by the ultrasound effect, which could afford more effective emulsification and make the extraction method greener. This technique was effectively coupled with a portable W-coil ET-AAS instrument to improve the analytical performance and expand the application of this spectrometer. Under the optimal conditions, the limit of detection (LOD) for bismuth was 0.2 μg L−1, with a sensitivity enhancement factor (EF) of 72. After routine optimization experiments accomplished in the lab, the developed coupling was applied to the field analysis of environmental samples with satisfactory analytical results.

Determination of Cr(VI) by portable tungsten coil electrothermal atomic absorption spectrometer after surfactant-assisted dispersive liquid-liquid microextraction

As a new developed instrument, a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) was first coupled with surfactant assisted dispersive liquid–liquid microextraction (SA-DLLME) to improve its analytical performance and expand its applications in this work. SA-DLLME was very simple, rapid and the extraction efficiency was considerably improved by the effect of surfactant, which was suitable to be coupled with the portable instrument in field analysis. After SA-DLLME, concentrated chromium in organic phase was directly determined on W-coil atomiser. The influence factors relevant to SA-DLLME and instrumental conditions were studied systematically. Under the optimal conditions, the limit of detection (LOD) for Cr(VI) was 0.016 µg L−1, with sensitivity enhancement factor (EF) of 107. The relative standard deviation (RSD) for seven replicate measurements of 0.5 µg L−1 of Cr(VI) was 4.6%. The recoveries for the spiked samples were in the acceptable range of 96.8–104%. The rapid, simple and high effective method greatly improved the sensitivity of this portable spectrometer for the determination of Cr(VI) and was applied to the analysis of ultra-trace Cr(VI) in real and certified water samples with satisfactory results.

Investigation of a portable tungsten coil electrothermal atomic absorption spectrometer for analysis of nickel after rapidly synergistic cloud point extraction

Rapidly synergistic cloud point extraction (RS-CPE) was coupled with tungsten coil electrothermal atomic absorption spectroscopy (W-coil ET-AAS) for the first time in this work. The extraction procedure using RS-CPE was very simple and accomplished in 1 min. The novel preconcentration technique was coupled with W-coil ET-AAS for nickel detection. The relevant factors and instrumental conditions that influence the RS-CPE were studied systematically. Under the optimal conditions, the limit of detection (LOD) was 0.2 μg L−1, with a sensitivity enhancement factor (EF) of 45. The relative standard deviation (RSD) for seven replicate measurements of 20 μg L−1 of nickel was 4.8%. The developed coupling was applied to the analysis of real and certified water samples with satisfactory results. In order to validate its application in field analysis, a number of environmental samples were studied.

Application of portable spectrometer for ultra trace metal analysis after ionic liquid based microextraction

In this work, a commercially available portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) was applied and investigated. The portable AAS instrument was developed based on a W-coil atomizer and a charge coupled device detector, and has the characteristics of compactness and portability. In this research, ionic liquid based liquid phase microextraction (IL-LPME) was coupled with a portable AAS instrument to expand its application and improve its analytical performance. Ultra trace lead and copper were investigated as the target elements in the established coupling. The factors influencing both IL-LPME and the portable spectrometer were optimized. Under the optimal conditions, the limits of detection for lead and copper were 0.25 μg L−1 and 0.10 μg L−1, with sensitivity enhancement factors of 38 and 26, respectively. The relative standard deviation (RSD) for seven replicate measurements of 20 μg L−1 of lead was 4.9%, and 10 μg L−1 of copper was 3.4%. The recoveries for the spiked samples were in the acceptable range of 92.7–105%.

A new coupling of ionic liquid based-single drop microextraction with tungsten coil electrothermal atomic absorption spectrometry

In this work, an improved method of ionic liquid based-single drop microextraction (IL-SDME) preconcentration was firstly coupled with tungsten coil electrothermal atomic absorption spectrometry (W-coil ET-AAS) detection. The new coupling was developed and applied for the determination of ultra-trace cadmium. Experimental parameters influencing the performance of IL-SDME as well as instrumental conditions were studied systematically, including IL-drop volume, chelating agent concentration, pH, stirring rate and time, heating program of W-coil ET-AAS, flow rate of carrier gas. Under the optimal conditions, the limit of detection (LOD) for cadmium was 0.015μgL−1 (sampling amount on W-coil was 10μL). The sensitivity enhancement factor was 42, while the improvement factor of LOD was 33. The established method was applied to determine cadmium in standard reference materials of rice and real water samples successfully. The developed IL-SDME-W-coil ET-AAS coupling represents a simple, green and highly sensitive method for cadmium determination.

Hollow fiber supported liquid membrane extraction for ultrasensitive determination of trace lead by portable tungsten coil electrothermal atomic absorption spectrometry

Hollow fiber supported liquid membrane extraction (HF-SLME) was used to separate and enrich trace lead from a large volume of 250 mL water sample to a final tiny volume of 30 μL of 1-octanol, 5 μL of which was inject into a tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) for determination of lead. Some important parameters that influenced the extraction and determination were investigated in detail, such as the concentration of ammonium pyrrolidine dithiocarbamate (APDC), pH of sample solution, stirring rate, extraction time, pyrolysis current, atomization current, carrier gas flow rate, as well as interferences. Under the optimized conditions, a practical enrichment factor of 499 and a limit of detection (3 σ) of 0.2 ng mL − 1 were obtained. The calibration curve was linear in the range of 0.5–10 ng mL − 1 . The relative standard deviation (RSD) was 5.6% for five measurements of a 4 ng mL − 1 lead standard solution. The accuracy of this method was examined by the analysis of certified reference water samples (GBW(E)080398 and GSBZ(E) 50009-88) for lead. Finally, the proposed method was applied to the determination of lead in local tap water, pond water and river water, with recoveries in the range of 96–109% for spiked samples.

Determination of cadmium in rice and water by tungsten coil electrothermal vaporization-atomic fluorescence spectrometry and tungsten coil electrothermal atomic absorption spectrometry after cloud point extraction

In this work, the microsampling nature of tungsten coil electrothermal vaporization Ar/H 2 flame atomic fluorescence spectrometry (W-coil ETV-AFS) as well as tungsten coil electrothermal atomic absorption spectrometry (W-coil ET-AAS) was used with cloud point extraction (CPE) for the ultrasensitive determination of cadmium in rice and water samples. When the temperature of the extraction system is higher than the cloud point temperature of the selected surfactant Triton X-114, the complex of cadmium with dithizone can be quantitatively extracted into the surfactant-rich phase and subsequently separated from the bulk aqueous phase by centrifugation. The main factors affecting the CPE, such as concentration of Triton X-114 and dithizone, pH, equilibration temperature and incubation time, were optimized for the best extract efficiency. Under the optimal conditions, the limits of detection for cadmium by W-coil ETV-AFS and W-coil ET-AAS were 0.01 and 0.03 μg L −1, with sensitivity enhancement factors of 152 and 93, respectively. The proposed methods were applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with certified values.

A comparative study of chemical modifiers in the determination of total arsenic in marine food by tungsten coil electrothermal atomic absorption spectrometry

Three platinum group elements (Pd, Ir and Rh) both in solution and in pre-reduced form, and also combined with Mg(NO 3) 2 or ascorbic acid, were assessed as possible chemical modifiers on the atomization of As in digest solutions of seafood matrices (clam and fish tissue) by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS) and compared without a modifier. Of 28 modifier alternatives in study including single form and binary mixtures, and based on maximum pyrolysis temperature without significant As loss and best As absorbance sensitivity during atomization, three modifiers: Rh (0.5 μg), Ir (1.0 μg) and Rh (0.5 μg) + ascorbic acid (0.5 μg), at optimum amounts were pre-selected and compared. The definitive modifier (rhodium (0.5 μg)) was selected by variance analysis. The mean within-day repeatability was 3% in consecutive measurements (25–300 μg l −1) (three cycles, each of n = 6) and showed good short-term stability of the absorbance measurements. The mean reproducibility was 4% ( n = 18 in a 3-day period) and the detection limit (3 σ blank/slope) was 42 pg ( n = 16). Quantitation was by standard additions to compensate for matrix effects not corrected by the modifier. Three sample digestion procedures were compared in fish and clam tissue samples: microwave acid digestion alone (A) or combined with the addition of 2% (m/v) K 2S 2O 8 solution followed either by UV photo-oxidation (B) or re-digestion in a thermal block (C). The accuracy was established by determination of As in certified reference material of dogfish muscle (DORM-2). Procedures B and C showed good recoveries (102% ( n = 4) and 103% ( n = 7), respectively), whereas procedure A was not quantitative (85%). The methodology is simple, fast, reliable, of low cost and was applied to the determination of total As in lyophilized samples of clam and fish collected in the Chilean coast.

Analytical Characteristics of a Continuum-Source Tungsten Coil Atomic Absorption Spectrometer

A continuum-source tungsten coil electrothermal atomic absorption spectrometer has been assembled, evaluated, and employed in four different applications. The instrument consists of a xenon arc lamp light source, a tungsten coil atomizer, a Czerny-Turner high resolution monochromator, and a linear photodiode array detector. This instrument provides simultaneous multi-element analyses across a 4 nm spectral window with a resolution of 0.024 nm. Such a device might be useful in many different types of analyses. To demonstrate this broad appeal, four very different applications have been evaluated. First of all, the temperature of the gas phase was measured during the atomization cycle of the tungsten coil, using tin as a thermometric element. Secondly, a summation approach for two absorption lines for aluminum falling within the same spectral window (305.5-309.5 nm) was evaluated. This approach improves the sensitivity without requiring any additional preconcentration steps. The third application describes a background subtraction technique, as it is applied to the analysis of an oil emulsion sample. Finally, interference effects caused by Na on the atomization of Pb were studied. The simultaneous measurements of Pb and Na suggests that negative interference arises at least partially from competition between Pb and Na atoms for H2 in the gas phase.

Chemical modifiers in arsenic determination in biological materials by tungsten coil electrothermal atomic absorption spectrometry.

Palladium, iridium, and rhodium are evaluated as possible chemical modifiers in the determination of As in digest solutions of biological materials (human hair and clam) by tungsten coil electrothermal atomic absorption spectrophotometry (TCA-AAS). The modifier in solution was applied onto the coil and thermally pre-reduced; the pre-reduction conditions, the amount of modifier, and the thermal program were optimized. Palladium was not satisfactory, whereas Ir and Rh were effective modifiers and rendered better relative sensitivity for As by a factor of 1.4 and 1.9, respectively compared to the case without modifier. Upon optimization of thermal conditions for As in pre-reduced Ir (2.0 microg) and Rh (2.0 microg) modifiers and in the digest solutions of the study matrices, Rh (2.0 microg) was more effective modifier and was selected as such. The mean within-day repeatability was 2.8% in consecutive measurements (25-100 microg L(-1)) (3 cycles, each of n=6) and confirmed good short-term stability of the absorbance measurements. The mean reproducibility was 4.4% (n=20 in a 3-day period) and the detection limit (3 sigmablank/slope) was 29 pg (n=15). The useful coil lifetime in Rh modifier was extended to 300-400 firings. Validation was by determination of As in the certified reference material (CRM) of "Oyster tissue" solution with a percentage relative error (Erel%) of 2% and percentage relative standard deviation (RSD%) of 3% (n=4), and by analytical recovery of As spiked in CRM of human hair [94 +/- 8% (n=4)]. The methodology is simple, fast (sample readout frequency 21 h(-1)), reliable, of low cost, and was applied to the determination of As in hair samples of exposed and unexposed workers.

Determination of dysprosium and europium in sheep faeces by graphite furnace and tungsten coil electrothermal atomic absorption spectrometry

Tungsten coil atomizer atomic absorption spectrometry (TCAAS) was used to determine Dy and Eu in acid-digested faeces of sheep. These elements were used as markers in animal nutrition studies. Samples were dried, ground and decomposed using a nitric–perchloric acid mixture. The accuracy of the developed method was evaluated by graphite furnace atomic absorption spectrometry (GFAAS). The results obtained for Eu were validated at a 95% confidence level using a paired t-test. The results for Dy were not validated owing to memory effects caused by carbide formation into the graphite tube. This effect did not occur for Eu. The detection limits for Dy and Eu were 6.9 and 2.1 μg l −1 by TCAAS, and 2.2 and 5.2 μg l −1 by GFAAS, respectively. Relative standard deviations (R.S.D.; n=5) were 0.7–3.8 and 0.8–5.6% for Dy and Eu by TCAAS and 0.8–5.4 and 0.3–3.8% for Dy and Eu by GFAAS, respectively. The lifetime of the tungsten coil was around 200 heating cycles, which is three-fold higher than graphite tube lifetime. The proposed method can be used to determine the passage rate of feed through animal digestive tract.

Determination of cadmium and lead in mussels by tungsten coil electrothermal atomic absorption spectrometry

In this work it was evaluated the determination of Cd and Pb in mussels by tungsten coil electrothermal atomic absorption spectrometry (TCA-AAS). A critical and comprehensive study of the effects caused by Pd, Mg, ascorbic acid, and binary mixtures of these compounds on the atomization of Cd and Pb in acid digested solutions of mussels was performed. Palladium and mixtures containing it were useful to increase sensitivity and thermal stability of Cd and Pb. Additionally, the coil lifetime was increased and the background signals were decreased in these modifiers. All these favorable effects were analytically exploited to determine Cd and Pb in samples of mussels. The proposed methodology was validated using two certified reference materials (oyster tissue and mussel). No statistical difference was observed between determined and certified values at a 95% confidence level. Cadmium and Pb in Chilean bivalve mussels were determined by TCA and by graphite furnace-AAS. Again, the results showed statistical agreement.

On-line coupling of electrochemical preconcentration in tungsten coil electrothermal atomic absorption spectrometry for determination of lead in natural waters

A flow injection system was coupled to a tungsten coil electrothermal atomizer (150 W) for on-line separation and preconcentration of lead based on its electrochemical reduction on the atomizer surface. The electrochemical cell is built up inside the furnace by using a Pt flow-through anode and the atomizer itself as the flow-through cathode. The manifold and the tungsten coil power supply were controlled by a computer running a program written in Visual Basic, which was utilized in synchronism with the original software of the atomic absorption spectrometer. The flow-through anode (50 mm long, 0.7 mm i.d.) was inserted in tip of the autosampler arm by replacing the last section of the PTFE sample delivering tube. The tungsten coil atomizer and the counter electrode were easily connected to a d.c. power supply. An enrichment factor of 25 was obtained for lead after a 120-s electrodeposition for a sample flowing at 1.0 ml min−1. The method detection limit was 0.2 μg l−1 Pb and the R.S.D.<5% (n=10 for 5 μg l−1 Pb). Up to 2% m/v NaCl or KCl and 5% m/v CaCl2 or MgCl2 did not interfere on the separation and atomization of 5 μg l−1 Pb.

Study of chemical modifiers for the determination of chromium in biological materials by tungsten coil electrothermal atomic absorption spectrometry

The determination of Cr in digest solutions of mussels and non-fat milk powder by tungsten coil elec- trothermal atomic absorption spectrophotometry (TC- ETAAS) is affected by interferences. This study reports a critical evaluation of chemical modifiers that could be em- ployed to correct these interferences. The chemical modi- fiers tested were: Mg (as Mg(NO3)2), Pd (as Pd(NO3)2), NH4NO3, ascorbic acid, and mixtures of these compounds . The less effective modifier was NH4NO3. The best effects, considering thermal stabilization and sensitivity, were ob- tained in mixtures of ascorbic acid plus Mg. Chromium was determined by TC-ETAAS in certified reference ma- terials of mussels and non-fat milk powder, and results were comparable with those obtained by graphite furnace atomic absorption spectrophotometry (GFAAS).

Atomization of Al in a tungsten coil electrothermal atomic absorption spectrophotometer

Electrothermal atomic absorption spectrophotometry of Al in a tungsten coil atomizer was evaluated and applied for its determination in hemodialysis fluid. The system was mounted on a Varian Spectra AA-40 spectrophotometer with continuum background correction and all measurements, in peak height absorbance, were done at 309.3 nm. The purge gas was a mixture of 90% Ar plus 10% H2. Observation height, gas flow, drying, pyrolysis and atomization steps were optimized. The heating program was carried out by employing a heating cycle in four steps: dry, pyrolysis, atomization and clean. The determination of Al in hemodialysis solutions was performed by using a matrix-matching procedure. Al in hemodialysis solutions was determined by TCA and by electrothermal atomization with a graphite tube atomizer. There is no differences between results obtained by both methods at a confidence level of 95%. The characteristic mass of Al by using the TCA was 39 pg and the detection limit was 2.0 μg l−1.

Determination of cadmium in hair and blood by tungsten coil electrothermal atomic absorption spectrometry with chemical modifiers

Three chemical modifiers ((NH4)2HPO4, NH4H2PO4, and Pd as Pd(NO3)2) were evaluated for the determination of Cd in acid-digested solutions of hair and blood using electrothermal atomic absorption spectrometry in a tungsten coil atomizer (TCA). All modifiers caused some thermal stabilization of Cd when compared to the behavior observed in nitric acid medium. The best effects were observed in 15 μg ml−1 Pd medium; the characteristic mass of Cd was 0.3 pg and the method detection limits were 0.009 μg g−1 in hair and 0.2 μg l−1 in blood. In addition to a slight thermal stabilization effect, Pd also increased the sensitivity for Cd by ca. 40% and the tungsten coil lifetime by 20% (i.e. from 300 to 360 heating cycles), reduced background signals, and eliminated condensed phase interferences caused by concomitants. The accuracy (3.2% as mean relative error in the Pd modifier) was checked for the determination of Cd in acid-digested solutions of certified reference materials of human hair and blood and by recoveries of Cd in spiked hair and blood samples by both TCA and a graphite furnace procedure. All results obtained in chemical modifiers are in agreement at a 95% confidence level.

Determination of Cobalt in Animal Feces by Tungsten Coil Atomic Absorption Spectrophotometry

An alternative analytical procedure for cobalt determination by tungsten coil electrothermal atomic absorption spectrophotometry (TCAAS) was developed to determine the liquid ruminal passage rate (turnover) of Co-EDTA in sheep feces. A matrix-matching procedure and a selective extraction of Co in 1.0 mol l-1 HCl were evaluated in order to correct and minimize the interference effects caused by sample matrices. As application, six sheep received at the same time one dose of the marker (Co-EDTA); thier fecal samples were collected in intervals of 6 h during 90 h. The Co amounts determined in the dry sheep feces by TCAAS were compared with those obtained by a flow injection catalytic spectrophotometric method. The characteristic mass and the detection limit, both based on peak height absorbance, were 23.1 and 19.1 pg, respectively, for 10 ml of sample volume in the samples of sheep feces. The rsd was 0.5% for 10 consecutive injections of 20.0 mg Co l-1. The accuracy was assessed by employing the paired t-test at 95% confidence level; there was no significant difference for Co content determined by TCAAS and by flow injection spectrophotometry.

Determination of ytterbium in animal faeces by tungsten coil electrothermal atomic absorption spectrometry

A method for ytterbium determination in animal faeces by tungsten coil electrothermal atomic absorption spectrometry (TCAAS) was developed. Faeces were dry-ashed in a muffle furnace, the ashes were treated with hydrochloric acid, and 10 μl of sample solution were delivered into 150-W tungsten coil atomizer. A matrix-matching procedure employing a 66-s heating program proved to be efficient for obtaining accurate results. Characteristic mass and detection limit were 7.1 pg and 0.35 μg g −1 Yb, respectively. The tungsten coil atomizer lifetime exceeded 300 firings with digested solutions and R.S.D. of measurements was 1.9% after ten consecutive injections of 10.0 μg l −1 Yb. Accuracy of the proposed method was assessed by employing a graphite furnace atomic absorption spectrometric procedure. Application of the paired t-test did not reveal any significant difference for ytterbium contents determined by both methods at 95% confidence level. It was demonstrated that the proposed procedure can successfully be used for evaluation of kinetic passage rate of feed through digestive tract of animals.