Preconcentration of trace lead by adsorption onto a tantalum wire for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer

A preconcentration method of lead in waters by adsorption on a tantalum wire was developed for electrothermal atomization atomic absorption spectrometry with a tungsten tube atomizer. After the preconcentration, the tantalum wire was directly inserted into the tungsten tube atomizer. In the preconcentration (adsorption) process for lead, the optimal immersing time was 90 s and the best pH was 4. Under the optimal conditions, the detection limit for lead by the tantalum wire preconcentration method was 6.0 pg mL^− 1 (3S/N) and the relative standard deviation was 6.1%. The influences of large amounts of concomitants on the preconcentration of lead were evaluated. Even though 10³ to 10⁴-fold excess of matrix elements existed in aqueous solution, the lead absorption signal was not significantly affected by the matrix elements. The method with preconcentration on a tantalum wire was applied to the determination of lead in river waters and proved to be sensitive, simple, and convenient. Because this preconcentration method can be utilized in the in-situ treatment of trace lead in environmental water samples, it was unnecessary to carry the water samples to the analytical work place. The present technique was shown to be useful for the determination of lead in environmental water samples at 0.1−1 μg L^− 1.     

Determination of manganese in herbal medicine samples by slurry-sampling electrothermal atomic absorption spectrometry with a metal tube atomizer

An ultrasonic slurry-sampling electrothermal atomic absorption spectrometry with a molybdenum tube atomizer has been developed for the determination of manganese in herbal medicine samples. Ten percent glycerol solution was used as the slurry medium. The optimum pyrolysis temperature was 400 degrees C. The detection limit was 69 fg (3xS/N). Matrix element interference was checked and it was found that glycerol as a chemical modifier eliminated the interference. The amounts of manganese in herbal medicines determined by the proposed method are in good accordance with those measured in dissolved acid-digested samples. The method enables rapid calibration, and simple and rapid analysis of manganese in herbal medicine samples at low cost.     

Atom formation processes for cadmium in the presence of sulphur in electrothermal atomization atomic absorption spectrometry with a molybdenum tube atomizer

The atom formation process that occurs during elimination by sulphur of interferences on cadmium in electrothermal atomization was studied by using a thermodynamic-kinetic equation and measuring x-ray diffraction patterns. Activation energies for cadmium in the presence of Al, Ca, Cr, Cu, Fe, K, Na or Pb were obtained in argon-hydrogen in the presence and absence of sulphur. The atom formation process for cadmium in the presence of sulphur was CdS(g) → Cd(g) in the presence of each interferent.     

Matrix modification by Cu(NO3)2 for the determination of gold by electrothermal atomic absorption spectrometry with a molybdenum tube atomizer

Matrix modification by copper nitrate in electrothermal atomic absorption Spectrometry (ETAAS) of gold with a molybdenum tube atomizer has been investigated. The addition of copper nitrate served to eliminate the interferences from 10⁴–10⁵-fold concentrations of foreign elements at the 890 °C pyrolysis temperature. The absolute characteristic mass (giving 0.0044 absorbance) of gold in the presence of copper nitrate with the Mo atomizer was 0.26 pg and the detection limit was 38 pg/ml. These values were several times better than those obtained with graphite atomizers. The recovery of spiked gold in biological materials was in the range 96–106%. A sensitive and accurate ETAAS method was developed for complex matrix samples.     

Direct determination of cadmium in biological material using electrothermal atomization atomic absorption spectrometry with a metal tube atomizer and a matrix modifier

A direct determination of cadmium by electrothermal atomization atomic absorption spectrometry with a molybdenum tube atomizer has been investigated. Direct calibration method with cadmium standard solutions and ultrasonic agitation method of a solution including sample powder were used. Sulfur served as a matrix modifier for removal of interferences. Though this direct analytical method for cadmium determination in biological materials had a relatively large standard deviation, the accuracy was similar or superior to those of a sample digestion method and the direct analysis without sulfur. The advantages of this method are its simplicity, low cost, high speed of analysis, and rapid calibration.     

Automatic flow system for the sequential determination of copper in serum and urine by flame atomic absorption spectrometry

In this work, a fully automated flow system exploiting the advantages of the association of multi-pumping, multicommutation, binary sampling and merging zones, to accomplish the sequential determination of copper in serum and urine by flame atomic absorption spectrometry, is described. The developed flow system allowed multiple tasks, such as serum samples preparation (samples and standard solutions viscosity adjustment), serum copper (SCu) measurement, urine copper (UCu) pre-concentration and its subsequent elution and measurement, to be carried out sequentially. The implemented flow manifold presented a modular configuration consisting on two quasi-independent modules, each one accountable for a specific sample manipulation and whose combined operation under computer control enabled the determination of copper in a wide concentrations range.Once optimised and with a sample consumption of about 0.250 mL of serum and 7 mL of urine, the developed flow system allowed linear calibration plots up to 5 mg L⁻¹ with a detection limit of 0.035 mg L⁻¹ for SCu and linear calibration plots up to 300 μg L⁻¹ with a detection limit of 0.67 μg L⁻¹ for UCu. The sampling rate varied according to the module employed and was about 360 determinations h⁻¹ (SCu module), 12 determinations h⁻¹ (UCu module) or 24 determinations h⁻¹ (12 urine and 12 serum samples; UCu and SCu modules simultaneously). Repeatability studies (R.S.D.%, n = 10) showed good precision for UCu at concentrations of 25 μg L⁻¹ (2.54%), 50 μg L⁻¹ (0.90%) and 100 μg L⁻¹ (1.62%) as well as for SCu at concentrations of 0.25 mg L⁻¹ (8.11%), 1 mg L⁻¹ (3.11%) and 5 mg L⁻¹ (0.90%). A comparative evaluation showed a good agreement between the results obtained in the analysis of UCu and SCu (n = 18) by both the developed methodology and the reference procedures. Accuracy was further evaluated by means of the analysis of reference samples (Seronorm™ Trace Elements Urine and Seronorm™ Trace Elements Serum) and the obtained results complied with the certified values.     

Slurry sampling techniques for the determination of lead in Bangladeshi fish samples by electrothermal atomic absorption spectrometry with a metal tube atomizer

Ultrasonic slurry sampling electrothermal atomic absorption spectrometry with a metal tube atomizer has been applied to the determination of lead in Bangladeshi fish samples. The slurry sampling conditions, such as slurry stabilizing agent, slurry concentration, pyrolysis temperature for the slurried fish samples, particle size and ultrasonic agitation time, were optimized for electrothermal atomic absorption spectrometry with the Mo tube atomizer. Thiourea was used as the chemical modifier for the interference of matrix elements. The detection limit was 53 fg (3S/N). The determined amount of lead in Bangladeshi fish samples was consistent with those measured in the dissolved acid-digested samples. The advantages of the proposed methods are easy calibration, simplicity, low cost and rapid analysis.     

超声辅助萃取-钨丝电热原子吸收光谱法测定痕量镉

镉对人体和动植物而言是一种非必需的元素,当其含量超过一定浓度就会产生毒性.由于镉在生物体内的半衰期长达1年之久,一旦进入生物体就不易排出.因此,测定食物样品中的镉对保证人类和动物的健康有重要的意义[1].     

Comparative study of magnesium nitrate,palladium nitrate and reduced palladium for the direct determination of mercury in sea water by electrothermal atomization atomic absorption spectrometry

A comparative study of different chemical modifiers in graphite furnace atomic absorption spectrometry for the direct determination of mercury in sea water samples, in synthetic sea water sample of high (72.8%) and low 34.2%) salinity and in aqueous solutions, was carried out. The use of reduced palladium produces better results. The mixture of palladium nitrate and ascorbic acid, gives the best limit of detection (1.9 gl^–1). The use of reduced palladium and magnesium nitrate produced excellent recoveries (close to 100%) in the whole salinity range for all mercury concentration tested. The use of palladium nitrate alone or combined with magnesium nitrate gave good recoveries with respect to a real sea water sample for low salinities. The interference from the major components of sea water were completely removed by using reduced palladium and magnesium nitrate modifiers. Thus, a single calibration curve with synthetic sea water may be applied to the analysis of sea water samples of widely differing salinities.     

Determination of vanadium and titanium in steel by inductively coupled plasma atomic emission spectrometry with modified use of a tungsten boat furnace atomizer for atomic absorption spectrometry

For electrothermal sample introduction, a commercially available tungsten boat atomizer for atomic absorption spectrometry (AAS) was transferred to a vaporizer for inductively coupled plasma atomic emission spectrometry (ICP-AES). The modification retained as much of the original design of the atomizer as possible, so that the apparatus could be switched easily between conventional tungsten boat furnace (TBF)-AAS and TBF-ICP-AES. By using this system, a procedure for the determination of vanadium and titanium in steel was investigated. The detection limits (S/N=3) of vanadium and titanium were 3.9 and 1.5 ng ml^?1, respectively. The relative standard deviations for five replicate determinations were ca. 3% for both elements. The calibration graphs were linear up to 100 μg ml^?1 vanadium(V) and 10 μg ml^?1 titanium(IV). Results of analyses of some low-alloy steel samples are given.     

Determination of cadmium in urine specimens by graphite furnace atomic absorption spectrometry using a fast atomization program

A simple, fast, and reliable method was developed for the determination of cadmium in urine specimens by graphite furnace atomic absorption spectrometry (GFAAS). The method involved dilution (1:1) of the specimens with a 4.0% HNO₃, direct injection of a 10 μl aliquot of the corresponding solution into a hot transversely-heated graphite atomizer (110 °C), and application of a fast atomization program (42 s) in which the conventional dry-pyrolysis sequence was substituted by a high-temperature (300 °C) drying step. The effect of the injection temperature (A), injection rate (B), pyrolysis’ ramp (C) and hold (D) times over the analyte’s integrated absorbance, peak-shape and repeatability of the measurements was evaluated by means of a 2^4-1 fractional factorial design. All those individual variables, as well as their first-order interactions (AB-, AC- and AD-type interactions) were found to exert a statistically significant effect (P<0.05). The lack of a chemical modifier other than the nitric acid itself benefited the overall methodology by allowing low-temperature atomization (1200 °C), enhanced atomic and background signals separation, and reduced blank values. A detection limit (3s, n=20) of 0.06 μg l⁻¹ Cd, corresponding to 0.12 μg l⁻¹ Cd in the urine specimen, and a characteristic mass of 1.78 pg/0.0044 s were obtained under the optimized conditions. The standard calibration technique (SCT) was used for quantitation. The successful determination of cadmium in Seronorm™ Trace Elements Urine Batch No. 115 (Nycomed Pharma AS) and in four urine specimens from volunteer donors (recoveries: 91.3-103.4%) attested to the robustness of the proposed method.     

Preconcentration of copper with multi-walled carbon nanotubes pretreated by potassium permanganate cartridge for solid phase extraction prior to flame atomic absorption spectrometry

A procedure for the preconcentration of copper was described in this paper using multi-walled carbon nanotubes (MWCNTs) oxidized by potassium permanganate as the adsorbent for the enrichment of trace copper in water samples. Important parameters, such as the sample pH, the concentration and volume of eluent, sample flow rate and volume, and interference of coexisting ions, were investigated. The obtained results indicated that proposed method possessed an excellent analytical performance. The linear range, the detection limit, and precison (RSD) were 1-100 ng/mL (R2 = 0.9993), 0.32 ng/mL and 2.88%, respectively. The results showed that copper could be adsorbed quantitatively on the pretreated MWCNTs with potassium permanganate, and proposed method was very useful in the monitoring of copper in the environment.     

Efficiency of Pt and Ir modifiers for the simultaneous determination of As, Se and In in a sodium sulphate matrix by electrothermal atomic absorption spectrometry

The effect of pre-reduced Pt and Ir modifiers towards simultaneous determination of As, Se and In in a sodium sulphate matrix was investigated. In spite of application of very isothermal THGA atomizer, negative influence of the matrix is pronounced. The efficiency of iridium modifier is somewhat higher than that of platinum modifier. However compared to palladium modifier both are significantly less effective in sulphate media. Taking into account our previous data, effectiveness of platinum group metal (PGM) modifiers in the determination of As, Se and In in the presence of sodium sulphate increases in the order Ru<Rh≈Pt<Ir<Pd. This order is opposite to the data on enthalpy of formation of PGM sulphides. This supports our hypothesis that effectiveness of PGM modifiers in the presence of sulphate matrix is determined mainly by stability of the corresponding sulphides. Efforts to enhance the effectiveness of Pt modifier mixing it with small (10-20%) amounts of Pd, Rh or Ir were not successful. Although mixture containing equal amounts of Pd, Pt, Rh and Ru is relatively effective, pure pre-reduced Pd is the best modifier for the simultaneous determination of As, Se and In in a sulphate media.     

Flow injection solid phase extraction electrothermal atomic absorption spectrometry for the determination of Cr(VI) by selective separation and preconcentration on a lab-made hybrid mesoporous solid microcolumn

A lab-made hybrid mesoporous solid was employed in a flow injection solid phase extraction electrothermal atomic absorption spectrometric (FI–SPE–ETAAS) system for the selective retention of Cr(VI). The solid was prepared by co-condensation of sodium tetraethylortosilicate and 3-aminopropyltriethoxysilane by sol–gel methodology and one-pot synthesis and characterized by Fourier transform infrared spectroscopy, X ray diffraction spectroscopy, and scanning electronic microscopy. Adsorption capacities at different pH values of both, Cr(VI) and Cr(III), were also measured in order to obtain the optimum retention for Cr(VI) with no interference of Cr(III). The maximum capacity of adsorption (4.35 mmol g^− 1) was observed for pH values between 2–3, whilst Cr(III) was found to remain in solution (adsorption capacity = 0.007 mmol g^− 1). Then, a microcolumn (bed volume: 7.9 µL) was filled with the solid and inserted in the FI–ETAAS system for analytical purposes. Since the analyte was strongly retained by the filling in the anionic form, 0.1 mol L^− 1 hydroxylammonium chloride in 1 mol L^− 1 hydrochloric acid was selected as eluent due to its redox characteristics. In this way, the sorbed Cr(VI) was easily released in the cationic form. The enrichment factor (EF) was found as a compromise between sensitivity and sample throughput and a value of 27 was obtained under optimized conditions: pH 2, sample loading 2 mL min^− 1 (60 s), elution flow rate 0.5 ml min^− 1 (eluent volume: 75 μL).     

Development of a cloud point extraction and preconcentration method for silver prior to flame atomic absorption spectrometry

The possibility was investigated of using 2-mercaptobenzothiazole (MBT) for Ag(I) concentration by micellar extraction at cloud point (CP) temperature and subsequent determination by flame atomic absorption spectrometry (FAAS). The method is based on the complexation of Ag(I) with 2-mercaptobenzothiazole (MBT) in the presence of non-ionic micelles of Triton X-114. The effect of experimental conditions such as pH, concentration of chelating agent and surfactant, equilibration temperature and time on cloud point extraction was studied. Under the optimum conditions, the preconcentration of 10 mL of water sample in the presence of 0.1% Triton X-114 and 2 × 10⁻⁴ mol L⁻¹ 2-mercaptobenzothiazole permitted the detection of 2.2 ng mL⁻¹ silver. The calibration graph was linear in the range of 10–200 ng mL⁻¹, and the recovery of more than 99% was achieved. The proposed method was used in FAAS determination of Ag(I) in water samples.     

Silica gel-polyethylene glycol as a new adsorbent for solid phase extraction of cobalt and nickel and determination by flame atomic absorption spectrometry

In this paper a novel solid phase extraction method to determine Co(II) and Ni(II) using silica gel-polyethylene glycol (Silica-PEG) as a new adsorbent is described. The method is based on the adsorption of cobalt and nickel ions in alkaline media on polyethylene glycol-silica gel in a mini-column, elution with nitric acid and determination by flame atomic absorption spectrometry. The adsorption conditions such as NaOH concentration, sample volume and amount of adsorbent were optimized in order to achieve highest sensitivity. The calibration graph was linear in the range of 0.5-200.0 ng mL⁻¹ for Co(II) and 2.0-100.0 ng mL⁻¹ for Ni(II) in the initial solution. The limit of detection based on 3S_b was 0.37 ng mL⁻¹ for Co(II) and 0.71 ng mL⁻¹ for Ni(II). The relative standard deviations (R.S.D.) for ten replicate measurements of 40 ng mL⁻¹ of Co(II), and Ni(II) were 3.24 and 3.13%, respectively. The method was applied to determine Co(II) and Ni(II) in black tea, rice flour, sesame seeds, tap water and river water samples.     

Ammonium pyrrolidinedithiocarbamate-modified activated carbon micro-column extraction for the determination of As(III) in water by graphite furnace atomic absorption spectrometry

A simple and selective method using ammonium pyrrolidinedithiocarbamate modified activated carbon (APDC-AC) as solid phase extractant has been developed for speciation of As(III) in water samples. At pH 1.8–3.0, As(III) could be adsorbed quantitatively by APDC-AC, and then eluted completely with 2.0 mL of 0.1 mol L⁻¹ HNO₃, while As(V) could almost not be retained at pH 1–7. Effects of acidity, sample flow rate, concentration of elution solution and interfering ions on the recovery of As(III) have been systematically investigated. Under the optimal conditions, the adsorption capacity of APDC-AC for As(III) is 7.3 mg g⁻¹. The detection limit (3σ) of As(III) is 0.05 ng mL⁻¹ for graphite furnace atomic absorption spectrometry (GFAAS) with enrichment factor of 50, and the relative standard deviation (RSD) is 4.1% (n = 9, C = 5 ng mL⁻¹). The method has been applied to the determination of trace As(III) in water, and the recoveries of As(III) are 100 ± 10%. Correspondence: Yiwei Wu, Department of Chemistry and Environmental Engineering, Hubei Normal University, Huangshi 435002, P.R. China     

Poly(etheretherketone)-turnings a novel sorbent material for lead determination by flow injection flame atomic absorption spectrometry and factorial design optimization

A novel hydrophobic sorbent material for on-line column preconcentration and separation systems coupled with atomic spectrometry was developed. Poly(etheretherketone) (PEEK) in the form of turnings was used as packing material and evaluated for trace lead determination in environmental samples. Sample and ammonium diethyl-dithiophosphate (DDPA) reagent were mixed on-line and the Pb(II)-DDPA complex was retained effectively on PEEK-turnings. Isobutyl methyl ketone (IBMK) was adopted for efficient analyte complex elution and subsequently transportation into the nebulizer-burner system for atomization. The developed sorbent material has shown, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates without significant loss of retention efficiency. For 120 s sample preconcentration time the sampling frequency was 20 h⁻¹, the enhancement factor was 110, the detection limit (3 s) was c_L = 0.32 μg L⁻¹, and the relative standard deviation (RSD) was s_R = 2.2%, at the 50.0 μg L⁻¹ Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials.     

Solid-phase extraction of Zn(II), Cu(II), Ni(II) and Pb(II) on poly(vinyl chloride) modified with 3-ferrocenyl-3-hydroxydithioacrylic acid, and their subsequent determination by electrothermal atomic absorption spectrometry

A new chelating resin based on poly(vinyl chloride) functionalized with 3-ferrocenyl-3-hydroxydithioacrylic acid has been synthesized and characterized. The resin was used as a packing material in an off-line mini-column solid-phase extraction system for preconcentration of Zn, Ni, Cu and Pb in water samples prior to their determination using electrothermal atomic absorption spectrometry. Analytical parameters such as pH, flow rate and sample breakthrough volume were optimized. The breakthrough volume for 0.2 μg of analyte using 0.1 g of adsorbent was 60–100 mL, permitting enrichment factors of at least 60. The proposed procedure, validated using a riverine water reference material (SLRS-3), was applied to environmental water samples. The potential for use of the chelating resin to separate interfering ions such as Na, K, Mg and Ca is also explored. Correspondence: Jackson K. Kiptoo, Department of Chemistry, Jomo Kenyatta University of Agriculture and Technology, P.O. Box 62000-00200, Nairobi, Kenya     

Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line prereduction of Se(VI) to Se(IV)

An on-line flow injection system has been developed for the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters by hydride generation atomic absorption spectrometry with microwave-aided heating prereduction of Se(VI) to Se(IV). The samples and the prereductant solutions (4 mol l⁻¹ HCl for Se(IV) and 12 mol l⁻¹ HCl for Se(VI)) which circulated in a closed-flow circuit were injected by means of a time-based injector. This mixture was displaced by a carrier solution of 1% v/v of hydrochloric acid through a PTFE coil located inside the focused microwave oven and mixed downstream with a borohydride solution to generate the hydride. The linear ranges were 0–120 and 0–100 μg l⁻¹ of Se(IV) and Se(VI), respectively. The detection limits were 1.0 μg l⁻¹ for Se(IV) and 1.5 μg l⁻¹ for Se(VI). The precision (about 2.0–2.5% RSD) and recoveries (96–98% for Se(IV) and 94–98% for Se(VI)) were good. Total selenium values were also obtained by electrothermal atomic absorption spectrometry which agreed with the content of both selenium species. The sample throughput was about 50 measurements per hour. The main advantage of the method is that the selective determination of Se(IV) and Se(VI) in citric fruit juices and geothermal waters is performed in a closed system with a minimum sample manipulation, exposure to the environment, minimum sample waste and operator attention.