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 (3σ) 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 paint samples by graphite furnace atomic absorption spectrometry with optical temperature control

A graphite furnace atomic absorption spectrometry (GFAAS) method with optical temperature control for the determination of trace cadmium in paint samples is described. Optical temperature control was superior in many respects to current temperature control. The sensibility increased by 60%, the linear range widened by 60%, and the life of graphite tube showed a 200–300% increase because atomization temperature was lowered distinctly and atomization time was shortened. Use of lanthanum chloride as a matrix modifier was investigated. The linear range of calibration curve was 0–24 ng mL⁻¹. The detection limit was 9.6 ng L⁻¹. The characteristic mass was 3.0 pg. The method also resulted in excellent reproducibility (≤2.5% R.S.D.) at such low levels, and the recovery of added cadmium in paint samples was from 94.6% to 102%. This method is readily applicable to the determination of cadmium in paint samples.     

Development of a new green non-dispersive ionic liquid microextraction method in a narrow glass column for determination of cadmium prior to couple with graphite furnace atomic absorption spectrometry

Easy and innovative non-dispersive ionic liquid based microextraction (NDILME) has been developed for preconcentration of trace level of cadmium (Cd) in aqueous real surface water samples prior to couple with graphite furnace atomic absorption spectrometry (GFAAS). A 200 cm long narrow glass column containing aqueous solution of standard/sample was used to increase phase transfer ratio by providing more contact area between two medium (aqueous and extractive), which drastically improve the recoveries of labile hydrophobic chelate of Cd ammonium pyrrolidinedithiocarbamate (APDC), into ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C₄mim][PF₆]. Different aspect of the desire method have been investigated and optimized. Under the optimized key experimental variables, limit of detection (LOD) and enhancement factor (EF) were achieved to be 0.5 ng L⁻¹ and 150, respectively. Reliability of the model method was checked by relative standard deviation (%RSD), which was found to be < 5%. Validity and accuracy of the developed method was checked by analysis of certified reference water samples (SLRS-4 Riverine water) using standard addition method.     

Dispersive liquid-liquid microextraction combined with graphite furnace atomic absorption spectrometry: ultra trace determination of cadmium in water samples

Dispersive liquid-liquid microextraction (DLLME) technique was successfully used as a sample preparation method for graphite furnace atomic absorption spectrometry (GF AAS). In this extraction method, 500 μL methanol (disperser solvent) containing 34 μL carbon tetrachloride (extraction solvent) and 0.00010 g ammonium pyrrolidine dithiocarbamate (chelating agent) was rapidly injected by syringe into the water sample containing cadmium ions (interest analyte). Thereby, a cloudy solution formed. The cloudy state resulted from the formation of fine droplets of carbon tetrachloride, which have been dispersed, in bulk aqueous sample. At this stage, cadmium reacts with ammonium pyrrolidine dithiocarbamate, and therefore, hydrophobic complex forms which is extracted into the fine droplets of carbon tetrachloride. After centrifugation (2 min at 5000 rpm), these droplets were sedimented at the bottom of the conical test tube (25 ± 1 μL). Then a 20 μL of sedimented phase containing enriched analyte was determined by GF AAS.Some effective parameters on extraction and complex formation, such as extraction and disperser solvent type and their volume, extraction time, salt effect, pH and concentration of the chelating agent have been optimized. Under the optimum conditions, the enrichment factor 125 was obtained from only 5.00 mL of water sample. The calibration graph was linear in the rage of 2-20 ng L⁻¹ with detection limit of 0.6 ng L⁻¹. The relative standard deviation (R.S.D.s) for ten replicate measurements of 20 ng L⁻¹ of cadmium was 3.5%. The relative recoveries of cadmium in tap, sea and rivers water samples at spiking level of 5 and 10 ng L⁻¹ are 108, 95, 87 and 98%, respectively. The characteristics of the proposed method have been compared with cloud point extraction (CPE), on-line liquid-liquid extraction, single drop microextraction (SDME), on-line solid phase extraction (SPE) and co-precipitation based on bibliographic data. Therefore, DLLME combined with GF AAS is a very simple, rapid and sensitive method, which requires low volume of sample (5.00 mL).     

Cloud point extraction for the determination of lead and cadmium in urine by graphite furnace atomic absorption spectrometry with multivariate optimization using Box–Behnken design

Cloud point extraction (CPE) is proposed as a pre-concentration procedure for the determination of Pb and Cd in undigested urine by graphite furnace atomic absorption spectrometry (GF AAS). Aliquots of 0.5 mL urine were acidified with HCl and the chelating agent ammonium O,O-diethyl dithiophosphate (DDTP) was added along with the non-ionic surfactant Triton X-114 at the optimized concentrations. Phase separation was achieved by heating the mixture to 50 °C for 15 min. The surfactant-rich phase was analyzed by GF AAS, employing the optimized pyrolysis temperatures of 900 °C for Pb and 800 °C for Cd, using a graphite tube with a platform treated with 500 μg Ru as permanent modifier. The reagent concentrations for CPE (HCl, DDTP and Triton X-114) were optimized using a Box–Behnken design. The response surfaces and the optimum values were very similar for aqueous solutions and for the urine samples, demonstrating that aqueous standards submitted to CPE could be used for calibration. Detection limits of 40 and 2 ng L^− 1 for Pb and Cd, respectively, were obtained along with an enhancement factor of 16 for both analytes. Three control urine samples were analyzed using this approach, and good agreement was obtained at a 95% statistical confidence level between the certified and determined values. Five real samples have also been analyzed before and after spiking with Pb and Cd, resulting in recoveries ranging from 97 to 118%.     

Hollow fiber supported liquid membrane microextraction of Cu2+ followed by flame atomic absorption spectroscopy determination

Hollow fiber supported liquid membrane microextraction, a relatively new sample preparation technique, has attracted much interest in the field of environmental analysis. In the current study, a novel method based on hollow-fiber liquid-phase microextraction and flame atomic absorption spectrometry (FAAS) for the measurement of copper ion in aqueous samples is described. Hollow-fiber liquid-phase microextraction conditions such as the type of extraction solvent, pH, the stirring rate, and the amounts of chelating agents, sample volume, and the extraction time were investigated. Under the optimized conditions, the linear range was found to be 0.01–15 μg ml^?1 for copper ion, and the limit of detection to be 0.004 μg ml^?1. Tap water and surface water samples collected from Mashhad, Iran and Dorongar river; Khorasan, Iran, respectively, were successfully analyzed using the proposed method. The recoveries from the spiked water samples were 72.4% and 105%, respectively; and the relative standard deviation (RSD) at the 2 μg ml^?1 level was 6%.     

Effectiveness of linearization of calibration curves in Zeeman graphite furnace atomic absorption spectrometry

A theoretical analysis is made of the effect of analytical line broadening and of non-absorbable radiation in the light source on the shape of concentration curves in Zeeman graphite furnace atomic absorption spectrometry. These results have been used in a systematic study of the effect of spectrometer slit width and hollow-cathode lamp (HCL) current on linearization of calibration graphs for 11 elements: Ag, Au, Bi, Cd, Co, Cu, Fe, Mn, Ni, Pb, and Sb. The effectiveness of linearization throughout the analytical range covered was estimated experimentally on series of 25–30 solutions. Three solutions in each series were used as standards for constructing the calibration graph, the others serving to evaluate the linearization effectiveness. Increasing the slit width and decreasing the HCL current compared to the standard measurement conditions have permitted us to reach a sufficiently high effectiveness of linearization for all the elements studied, with the exception of Ni. The maximum deviation of experimental points from the linear graph under optimum conditions does not exceed 6%. The effect of the Δ parameter used in the computational algorithm on linearization effectiveness is investigated.     

石墨炉原子吸收法测定石脑油中微量砷

试样用四氢呋喃（THF）有机溶剂稀释,以硝酸镍为基体改进剂,研究采用石墨炉原子吸收法直接进样测定石脑油中的砷量。研究表明,砷量在0～50μg／L范围内线性关系良好,回收率93％～104％。     

浊点萃取-石墨炉原子吸收光谱法测定水样中痕量铝

提出了浊点萃取石墨炉原子吸收光谱法测定痕量铝的新方法。探讨了溶液pH、试剂浓度等实验条件对浊点萃取及测定灵敏度的影响。在最佳条件下,富集40 mL样品溶液,用石墨炉原子吸收光谱法测定,铝的检出限为0.045μg/L,铝的富集倍率为78.5倍。方法适用于自来水、河水及海水中痕量铝的测定。     

Determination of cadmium in coal using solid sampling graphite furnace high-resolution continuum source atomic absorption spectrometry

This work describes the development of a method to determine cadmium in coal, in which iridium is used as a permanent chemical modifier and calibration is performed against aqueous standards by high-resolution continuum source atomic absorption spectrometry (HR-CS AAS). This new instrumental concept makes the whole spectral environment in the vicinity of the analytical line accessible, providing a lot more data than just the change in absorbance over time available from conventional instruments. The application of Ir (400 g) as a permanent chemical modifier, thermally deposited on the pyrolytic graphite platform surface, allowed pyrolysis temperatures of 700 °C to be used, which was sufficiently high to significantly reduce the continuous background that occurred before the analyte signal at pyrolysis temperatures <700 °C. Structured background absorption also occurred after the analyte signal when atomization temperatures of >1600 °C were used, which arose from the electron-excitation spectrum (with rotational fine structure) of a diatomic molecule. Under optimized conditions (pyrolysis at 700 °C and atomization at 1500 °C), interference-free determination of cadmium in seven certified coal reference materials and two real samples was achieved by direct solid sampling and calibrating against aqueous standards, resulting in good agreement with the certified values (where available) at the 95% confidence level. A characteristic mass of 0.4 pg and a detection limit of 2 ng g^–1, calculated for a sample mass of 1.0 mg coal, was obtained. A precision (expressed as the relative standard deviation, RSD) of <10% was typically obtained when coal samples in the mass range 0.6–1.2 mg were analyzed.Dedicated to the memory of Wilhelm Fresenius     

石墨炉原子吸收光谱法测定茶叶中的铅

采用石墨炉原子吸收光谱法测定茶叶中铅,以NH4H2PO4作为基体改进剂,提高了测定的灰化温度,消除了基体干扰.方法简便,快速,准确度高.通过对标准物质的多次测定,结果均在其保证值范围内,相对标准偏差为2.8%.对样品进行加标回收试验,回收率为96%～105%,方法检出限为0.12μg/L.     

石墨炉原子吸收法测定3-苯基丙烯酸酯类化合物中微量钯

利用高灵敏的石墨炉原子吸收法,在V(HCl):V(HNO3):V(H2O)＝5:1:94混合酸介质中测定苯基丙烯酸酯类化合物中的钯量.已纯化样品钯量的平均值是6.76 μg/g,标准相对偏差是4.8%,平均回收率为99.3%;未纯化样品钯量的平均值是121.2 μg/g,平均相对偏差是5.4%.还讨论酸介质对测定钯吸光度的影响,通过比较找到了合适的酸介质组成.     

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.     

Hollow fiber supported liquid membrane extraction coupled with thermospray flame furnace atomic absorption spectrometry for the speciation of Sb(III) and Sb(V) in environmental and biological samples

A new method of hollow fiber supported liquid membrane extraction (HF-SLME) coupled with thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for the speciation of Sb(III) and Sb(V) in environmental and biological samples has been developed. The method is based on the complex of Sb(III) with sodium diethyldithiocarbamate (DDTC). The formed hydrophobic complex is subsequently extracted into the lumen of hollow fiber, whereas Sb(V) is remained in aqueous solutions. The extraction organic phase was injected into TS-FF-AAS for the determination of Sb(III). Total Sb concentration was determined after reduction of Sb(V) to Sb(III) in the presence of l-cysteine and the extraction procedure mentioned above. Sb(V) was calculated by subtracting of Sb(III) from the total Sb. DDTC was used as complexing reagent. 1-Octanol was immobilized in the pores of the polypropylene hollow fiber as liquid membrane and also used as the acceptor solution. Some parameters that influenced extraction and determination were evaluated in detail, such as concentration of sodium diethyldithiocarbamate (DDTC), type of organic solvent, pH of samples, stirring rates, extraction time, as well as interferences. Under optimized conditions, a detection limit of 0.8 ng mL⁻¹ and an enrichment factor of 160 were achieved. The relative standard deviation (RSD) was 6.2% for Sb(III) (50 ng mL⁻¹, n = 5). The proposed method was successfully applied to the speciation of Sb(III) and Sb(V) in environmental and biological samples with satisfactory results.     

Different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry: Cadmium determination in whole blood as a case study

In the present work the performance of different platform and tube geometries and atomization temperatures in graphite furnace atomic absorption spectrometry was investigated, using the determination of Cd in whole blood as an example. Grooved, integrated and fork platforms as well as atomization temperatures between 1200 °C and 2200 °C were investigated in a longitudinally heated graphite atomizer and compared with the performance of a transversely heated furnace. In the longitudinally heated furnace the increase of the atomization temperature in the studied range resulted in an increase of matrix effects for all platform geometries. The integrated platform exhibited slightly lower sensitivity and increased multiplicative interferences in comparison to the other two platform designs. Interference-free Cd determination was possible with all types of platforms and 1200 °C as the atomization temperature as well as with grooved and fork platforms at 1700 °C. On the other hand, lower atomization temperatures resulted in poorer limits of detection, due to the longer integration time needed. No matrix effect was observed at any atomization temperature using the transversely heated atomizer; in addition, limits of detection were better than those observed with the longitudinally heated atomizer. Best values were around 0.02 μg L^− 1 with the latter atomizer compared to values around 0.02 μg L^− 1 with the former one.     

Increasing the working calibration range by means of artificial neural networks for the determination of cadmium by graphite furnace atomic absorption spectrometry

Feed-forward artificial neural networks (ANNs), trained with the generalized delta rule, were evaluated for modeling the non-linear behavior of calibration curves and increasing the working range for the determination of cadmium by graphite furnace atomic absorption spectrometry (GFAAS). Selection of this analyte was made on the basis of its short linear range (up to 4.0 μg l⁻¹). Two-layer neural networks, comprising one node in the input layer (linear transfer function); a variable number of neurons in the hidden layer (sigmoid transfer functions), and a single neuron (linear transfer function) in the output layer were assessed for such a purpose. The (1:2:1) neural network was selected on the basis of its capacity to adequately model the working calibration curve in the range of study (0-22.0 μg l⁻¹ Cd). The latter resulted in a nearly six fold increase in the working range. Cadmium was determined in the certified reference material “Trace Elements in Drinking Water” (High Purity Standards, Lot No. 490915) at four concentration levels (2.0, 4.0, 8.0 and 12.0 μg l⁻¹ Cd), which were experimentally within and above the linear dynamic range (LDR). No significant differences (P<0.05) were found between the expected concentrations and the results obtained by means of the neural network. The proposed method was compared with the conventional “dilution” approach, and with fitting the working calibration curve by means of a second-order polynomial. Modeling by means of an ANN represents an alternative calibration technique, for its use helps in reducing sample manipulation (due to the extension of the working calibration range), and may provide higher accuracy of the determinations in the non-linear portion of the curve (as a result of the better fitness of the model).     

二苯硫脲-醋酸丁酯萃取-石墨炉原子吸收法测定地球化学样品中痕量银

对石墨炉原子吸收光谱法测定地球化学样品中痕量银进行了研究。样品经盐酸、硝酸、硫酸、高氯酸溶解,在盐酸(1.2mol/L)介质中用醋酸丁酯萃取银与二苯硫脲螯合物,用石墨炉原子吸收光谱法测定地球化学样品中痕量银,方法检出限为0.011ng/mL,相对标准偏差(RSD,n=11)为6.0%~12.2%,加标回收率为96.00%~105.00%。能满足地球化学样品中银含量为0.02~5μg/g范围内银测定的准确度和精密度的要求。     

Evaluation of ammonia as diluent for serum sample preparation and determination of selenium by graphite furnace atomic absorption spectrometry

A method for the determination of total selenium in serum samples by graphite furnace atomic absorption spectrometry was evaluated. The method involved direct introduction of 1:5 diluted serum samples (1% v/v NH₄OH+0.05% w/v Triton X-100^®) into transversely heated graphite tubes, and the use of 10 μg Pd+3 μg Mg(NO₃)₂ as chemical modifier. Optimization of the modifier mass and the atomization temperature was conducted by simultaneously varying such parameters and evaluating both the integrated absorbance and the peak height/peak area ratio. The latter allowed the selection of compromise conditions rendering good sensitivity and adequate analyte peak profiles. A characteristic mass of 49 pg and a detection limit (3s) of 6 μg 1⁻¹ Se, corresponding to 30 μg l⁻¹ Se in the serum sample, were obtained. The analyte addition technique was used for calibration. The accuracy was assessed by the determination of total selenium in Seronorm™ Trace Elements Serum Batch 116 (Nycomed Pharma AS). The method was applied for the determination of total selenium in ten serum samples taken from individuals with no known physical affection. The selenium concentration ranged between 79 and 147 μg l⁻¹, with a mean value of 114±22 μg l⁻¹.     

Solid-phase extraction of bismuth, lead and nickel from seawater using silica gel modified with 3-aminopropyltriethoxysilane filled in a syringe prior to their determination by graphite furnace atomic absorption spectrometry

In this study, the use of syringe filled with sorbent for the separation and enrichment of bismuth, lead and nickel prior to their analysis by graphite furnace atomic absorption spectrometry was described to substitute for batch and column techniques. The method proposed in this paper was compared with column technique with respect to easiness, fastness, simplicity, recovery and risk of contamination. The syringe was filled with 0.5 g of sorbent and in order to retain the analyte elements, 5 ml of sample solution (pH≥5) was drawn into the syringe to 15 s and discharged again in 15 s. Then, 2.0 M of HCl, as the eluent, was drawn into the syringe and ejected back to desorb the analyte elements. At optimum conditions, the recoveries of Bi, Pb and Ni were 95-99% with relative standard deviations (RSDs) of around ±2%. Detection limit (δ) was 0.5 μg l⁻¹ for Bi, Pb and Ni, respectively. The elements could be concentrated by drawing and discharging several portions of sample successively but eluting only one time. Bi, Pb and Ni added to a seawater sample were quantitatively recovered (>95%) with low RSD values of around ±2-3%. The risk of contamination is less than that with the column technique. In addition, it is much faster, simpler, easier, more practical and handy compared with column technique.     

Dispersive liquid-liquid microextraction preconcentration of palladium in water samples and determination by graphite furnace atomic absorption spectrometry

A new method for the determination of palladium was developed by dispersive liquid-liquid microextraction preconcentration and graphite furnace atomic absorption spectrometry detection. In the proposed approach, diethyldithiocarbamate (DDTC) was used as a chelating agent, and carbon tetrachloride and ethanol were selected as extraction and dispersive solvent. Some factors influencing the extraction efficiency of palladium and its subsequent determination, including extraction and dispersive solvent type and volume, pH of sample solution, concentration of the chelating agent and extraction time, were studied and optimized. Under the optimum conditions, the enrichment factor of this method for palladium reached at 156. The detection limit for palladium was 2.4 ng L⁻¹ (3σ), and the relative standard deviation (R.S.D.) was 4.3% (n = 7, c = 1.0 ng mL⁻¹). The method was successfully applied to the determination of trace amount of palladium in water samples.