Sequential molecular vapor elution analysis for the separation and determination of LiCl and NaCl in river waters

The determination of alkali metal chloride in river waters by sequential molecular vapor elution analysis (SMVEA) using a molecular absorption detector (MA) is reported. An improved molybdenum column was developed for SMVEA. An optimum flow rate of carrier gas (pure argon or nitrogen) for separation of metal vapors was 12.0 ml min⁻¹. Lithium chloride and sodium chloride peaks completely separated from potassium, rubidium, and cesium chlorides but CaCl₂, FeCl₂, MgCl₂, and MnCl₂ peaks did not appear at a column temperature of 1000 °C and vaporization temperature of 1000 °C. The appearing order of these metal chlorides was LiCl, NaCl, KCl, RbCl, and CsCl. It was not understood by considering the boiling points of these metal chlorides. The delay of appearing time is due to an interaction between the molecular vapors and inside surface of the column. Under the experimental conditions, the number of theoretical plates was 247 for LiCl and 268 for NaCl in the improved column. Under the optimal experimental conditions, river waters were analyzed for lithium and sodium chlorides. The analytical results agreed well with the recoveries were in the range of 94–105%. By SMVEA, it was found that lithium and sodium chlorides in waters were determined without interference of matrix elements, no chemical treatment for river water samples.     

Determination of cadmium and lead in river water by sequential metal vapor elution analysis using a step-heated column

Determination of cadmium and lead in river water by sequential metal vapor elution analysis (SMVEA, column temperature; >1210 K) with argon carrier gas and an atomic absorption detector (AA) is reported. The column was a molybdenum tube inserted a tungsten coil. The flow rate of carrier gas was 1.8 ml min^–1. Cadmium and lead were separated from Ca, Fe, K, Na, and Zn metal vapours by SMVEA with the step-heated column (1210–1520 K) at an atomization temperature of 1830 K. Under the optimal experimental conditions, the recoveries of spiked-cadmium and lead in river waters were in the range of 91 to 106%. It is to determine cadmium and lead in river water without the interferences by matrix elements observed by electrothermal AAS, after only the addition of hydrochloric acid to the sample.     

流动注射在线萃取-火焰原子吸收法测定食用盐中的锌

基于锌与 1 (2 吡啶偶氮 ) 2 萘酚 (简称PAN)形成的配合物可被氯仿萃取 ,从高盐基体样品中分离富集锌 ,利用自行设计的分相器 ,实验确定了最佳的流动注射在线萃取 火焰原子吸收光度法测定锌的流路系统和化学反应条件。在选定的工作条件下 ,其RSD和检出限分别为 4 3 % (c=0 6 μg/mL ,n =1 1 )和0 0 3 μg/mL ,测定速度为 2 5样 /h。用于实际样品的测定 ,加标回收率为 97%～1 0 6 %。     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Analysis of organomercury compounds in sediments by capillary GC with atomic fluorescence detection

Analysis of methyl- and ethylmercury (MM and EM) halides in biological and environmental samples is generally performed by gas chromatography with electron capture detection. Tedious sample work-up protocols and poor chromatographic response (using packed columns) have, however, shown the need for the development of new methods in this field. This paper reports a sensitive method, free from these deficiencies, for the determination of methyl- and ethylmercury. The organomercury compounds (MM and EM) are first released from the sample matrix, by the combined action of acidic potassium bromide and cupric ions, and then extracted into dichloromethane. The initial extracts are subjected to thiosulfate clean-up and the organomercury species are isolated as their chloride derivatives by addition of cupric chloride, and subsequent extraction into a small volume of organic solvent. Capillary GC coupled with atomic fluorescence detection provided excellent separation efficiencies for methyl- and ethylmercury and proved to be a very selective and sensitive technique. The absolute detection limit for both MM and EM was found to be 0.2 pg.     

Determination of calcium, magnesium and zinc in unused lubricating oils by atomic absorption spectroscopy

Varying concentrations of lanthanum and strontium were added to solutions of ashed unused lubricating oils for the determination of calcium, magnesium and zinc content using flame atomic absorption spectrophotometry. At least 3000 μg g⁻¹ of lanthanum or strontium was required to completely overcome the interference of the phosphate ion, PO³⁻₄, and give peak values for calcium. The presence of lanthanum or strontium did not cause an appreciable increase in the amount of magnesium and zinc obtained from the analyses. The method is fast and reproducible, and the coefficients of variation calculated for the elements using one of the samples were 1.6% for calcium, 3.5% for magnesium and 0.2% for zinc. Results obtained by this method were better than those obtained by other methods for the same samples.     

On-line elimination of spectral interference of iron matrix in the flame atomic absorption determination of zinc by anion-exchange separation

A flow injection analysis (FIA) system has been developed for the flame atomic absorption spectroscopic (FAAS) determination of zinc in iron matrix. The spectral line interference of iron at 213.859 nm was eliminated by on-line separation using a micro-column of strong anion-exchange resin (Dowex 1-X8). The zinc chloro complexes were retained from 2 M HCl solution while most of the iron chloro complexes were passed to waste. For a 2% iron solution, matrix removal efficiency was 98.2% which means that positive spectral line interference of iron at the Zn line was reduced from 0.42 to 0.008 μg ml⁻¹ Zn. The optimized flow injection system can handle up to 48 samples with good precision (less than 3.5% relative standard deviation (R.S.D.)) in the working range of 0.075-2.2 μg ml⁻¹ Zn. Comparative analysis of a certified reference material and synthetic sample solutions containing traces of Zn in 2% Fe by the proposed method and by graphite furnace atomic absorption spectroscopy (GFAAS) showed no evidence of analytical bias at the 95% confidence level.     

火焰原子吸收光谱法分析沉积物中重金属元素的形态

采用原子吸收光谱法研究了金沙江攀枝花段水系沉积物中重金属的形态及分布特征。研究发现,各重金属的形态以残渣态为主,离子交换态含量很少。同时说明原子吸收光谱法完全可以用来研究重金属形态特征,在环境研究中具有重要意义。     

Study of interferences by transition metal ions in hydride generation atomic absorption spectrometry of antimony

The mechanism of the interference of metal ions in the hydride generation atomic absorption spectrometry (AAS) of antimony was studied. Experiments on the decomposition rate of sodium tetrahydroborate in acidic media were done in the presence of interfering metals, with and without the addition of masking agents. The results were compared with experiments on the sensitivity of AAS in the presence of the same interfering metals with and without the addition of the same masking agents. AAS experiments are described in which the product of the reaction between sodium tetrahydroborate and one of the interfering metals was present during hydride formation. This reaction product was certainly one of the causes of interference, but the contribution of the catalytic decomposition of sodium tetrahydroborate to interference is not clear.     

Speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry

A simple procedure was developed for the speciation of inorganic arsenic by electrochemical hydride generation atomic absorption spectrometry (EcHG–AAS), without pre-reduction of As(V). Glassy carbon was selected as cathode material in the flow cell. An optimum catholyte concentration for simultaneous generation of arsine from As(III) and As(V) was 0.06 mol l⁻¹ H₂SO₄. Under the optimized conditions, adequate sensitivity and difference in ratio of slopes of the calibration curves for As(III) and As(V) can be achieved at the electrolytic currents of 0.6 and 1 A. The speciation of inorganic arsenic can be performed by controlling the electrolytic currents, and the concentration of As(III) and As(V) in the sample can be calculated according to the equations of absorbance additivity obtained at two selected electrolytic currents. The calibration curves were linear up to 50 ng ml⁻¹ for both As(III) and As(V) at 0.6 and 1 A. The detection limits of the method were 0.2 and 0.5 ng ml⁻¹ for As(III) and As(V) at 0.6 A, respectively. The relative standard deviations were of 2.1% for 20 ng ml⁻¹ As(III) and 2.5% for 20 ng ml⁻¹ As(V). The method was validated by the analysis of human hair certified reference material and successfully applied to speciation of soluble inorganic arsenic in Chinese medicine.     

Determination of aluminum by electrothermal atomic absorption spectroscopy in lubricating oils emulsified in a sequential injection analysis system

The sequential injection (SIA) technique was applied for the on-line preparation of an “oil in water” microemulsion and for the determination of aluminum in new and used lubricating oils by electrothermal atomic absorption spectrometry (ET AAS) with Zeeman-effect background correction. Respectively, 1.0, 0.5 and 1.0 ml of surfactants mixture, sample and co-surfactant (sec-butanol) solutions were sequentially aspirated to a holding coil. The sonication and repetitive change of the flowing direction improved the stability of the different emulsion types (oil in water, water in oil and microemulsion). The emulsified zone was pumped to fill the sampling arm of the spectrometer with a sub-sample of 200 μl. Then, 10 μl of this sample solution were introduced by means of air displacement in the graphite tube atomizer. This sequence was timed to synchronize with the previous introduction of 15 μg of Mg(NO₃)₂ (in a 10 μl) by the spectrometer autosampler. The entire SIA system was controlled by a computer, independent of the spectrometer. The furnace program was carried out by employing a heating cycle in four steps: drying (two steps at 110 and 130 °C), pyrolisis (at 1500 °C), atomization (at 2400 °C) and cleaning (at 2400 °C). The calibration graph was linear from 7.7 to 120 μg Al l⁻¹. The characteristic mass (mo) was 33.2 pg/0.0044 s and the detection limit was 2.3 μg Al l⁻¹. The relative standard (RSD) of the method, evaluated by replicate analyses of different lubricating oil samples varied in all cases between 1.5 and 1.7%, and the recovery values found in the analysis of spiked samples ranged from 97.2 to 100.4%. The agreement between the observed and reference values obtained from two NIST Standard Certified Materials was good. The method was simple and satisfactory for determining aluminum in new and used lubricating oils.     

Analysis of kaolin by sedimentation field-flow fractionation and electrothermal atomic absorption spectrometry detection

Summary Electrothermal (graphite furnace) atomic absorption spectrometry (ETAAS), as off-line detector for sedimentation field-flow fractionation (SedFFF) is exploited in clay analysis. Quantitation limits of coupled SedFFF-ETAAS for the determination of a submicron kaolin sample, considered a representative model of natural water suspended particulate, are theoretically established and experimentally validated with reference to Al and Si determination by ETAAS. Complete sample recovery for a 4 μg injected kaolin sample was obtained by keeping adsorption in the SedFFF apparatus to a minimum under control. The best experimental conditions, ensuring sample integrity, were low ionic strength (Na₂CO₃, 10⁻⁵ M), pH 8 and a Teflon covered accumulation wall. Several different runs, revealing the various experimental parameters affecting quantitative recovery, are reported and the different physico-chemical processes affecting such recovery are discussed. The advantages and drawbacks of SedFFF-ETAAS coupling compared with inductively coupled plasma-mass spectrometry (ICP-MS) technique are also discussed.     

石墨炉原子吸收法测定肼类推进剂中九种金属杂质

建立了石墨炉原子吸收法测定肼类推进剂中锌、铁、铬、锰、铅、镍、铝、铜、钛等金属含量的检测方法 ,无需样品预处理过程 ,灵敏度高且快速、准确。各元素测定方法的精密度小于 1 0 % ,回收率在 82 %～ 1 1 6%之间。     

Element-selective atomic emission detection for capillary GC of metal-containing compounds

Element-selective GC detection by microwave-induced plasma atomic emission spectroscopy has been used to examine a wide variety of compounds containing metals, non-metals, and metalloids. “Recipes”, or new selective detection schemes for use with the software of the computer-controlled system, have been developed for the selective detection of boron, aluminum, gallium, titanium, vanadium, chromium, manganese, rhenium, palladium, and platinum. Figures of merit including limits of detection, linear dynamic range, and spectral selectivity over carbon have been established for most of these elements. Gas chromatography – atomic emission detection (GC-AED) has been applied to the selective detection of vanadium, nickel, and iron in metalloporphyrins present in crude oil, manganese-selective detection of methylcyclopentadienylmanganese tricarbonyl (MMT) in gasoline, and titanium-selective detection of reaction mixtures containing titanium catalysts or titanium boride molecular precursors.     

Speciation analysis of mercury in water samples by cold vapor atomic absorption spectrometry after preconcentration with dithizone immobilized on microcrystalline naphthalene

Trace amounts of inorganic mercury (Hg²⁺) and methylmercury cations (MeHg²⁺) were adsorbed quantitatively from acidic aqueous solution onto a column packed with immobilized dithizone on microcrystalline naphthalene. The trapped mercury was eluted with 10 ml of 7 mol L^–1 hydrochloric acid solution. The Hg²⁺ was then directly reduced with tin (II) chloride, and volatilized mercury was determined by cold vapor atomic absorption spectrometry (CVAAS). Total mercury (Hgt) was determined after decomposition of MeHg⁺ into Hg²⁺. Hg²⁺ and MeHg⁺ cations were completely recovered from the water with a preconcentration factor of 200. The relative standard deviation obtained for eight replicate determinations at a concentration of 0.3 g L^–1 was 1.8%. The procedure was applied to analysis of water samples, and the accuracy was assessed via recovery experiment.     

Hyphenation of flow injection/sequential injection with chemical hydride/vapor generation atomic fluorescence spectrometry

The dominant role played by flow injection/sequential injection (FI/SI, including lab-on-valve, LOV) in automatic on-line sample pretreatments coupling to various detection techniques is amply demonstrated by the large number of publications it has given rise to. Among these, its hyphenation with hydride/vapor generation atomic fluorescence spectrometry (HG/VG-AFS) has become one of the most attractive sub-branches during the last years, attributed not only to the high sensitivity of this technique, but also to the superb separation capability of hydride/vapor forming elements from complex sample matrices. In addition, it also provides potentials for the speciation of the elements of interest.It is worth mentioning that quite a few novel developments of sample pretreatment have emerged recently, which attracted extensive attentions from the related fields of research. The aim of this mini-review is thus to illustrate the state-of-the-art progress of implementing flow injection/sequential injection and miniaturized lab-on-valve systems for on-line hydride/vapor generation separation and preconcentration of vapor forming elements followed with detection by atomic fluorescence spectrometry, within the period from 2004 up to now. Future perspectives in this field are also discussed.     

Speciation analysis of inorganic arsenic by a multisyringe flow injection system with hydride generation-atomic fluorescence spectrometric detection

In this study, a new technique by hydride generation-atomic fluorescence spectrometry (HG-AFS) for determination and speciation of inorganic arsenic using multisyringe flow injection analysis (MSFIA) is reported. The hydride (arsine) was generated by injecting precise known volumes of sample, a reducing sodium tetrahydroborate solution (0.2%), hydrochloric acid (6 M) and a pre-reducing solution (potassium iodide 10% and ascorbic acid 0.2%) to the system using a multisyringe burette coupled with one multi-port selection valve. This solution is used to pre-reduce As(V) to As(III), when the task is to speciate As(III) and As(V). As(V) is determined by the difference between total inorganic arsenic and As(III). The reagents are dispensed into a gas-liquid separation cell. An argon flow delivers the arsine into the flame of an atomic fluorescence spectrometer. A hydrogen flow has been used to support the flame. Nitrogen has been employed as a drier gas (Fig. 1).Several variables such as sample and reagents volumes, flow rates and reagent concentrations were investigated in detail. A linear calibration graph was obtained for arsenic determination between 0.1 and 3 μg l⁻¹. The detection limit of the proposed technique (3σ_b/S) was 0.05 μg l⁻¹. The relative standard deviation (R.S.D.) of As at 1 μg l⁻¹ was 4.4 % (n = 15). A sample throughput of 10 samples per hour was achieved. This technique was validated by means of reference solid and water materials with good agreement with the certified values. Satisfactory results for speciation of As(III) and As(V) by means of the developed technique were obtained.     

Evaluation of a novel PTFE material for use as a means for separation and preconcentration of trace levels of metal ions in sequential injection (SI) and sequential injection lab-on-valve (SI-LOV) systems: Determination of cadmium(II) with detection by electrothermal atomic absorption spectrometry (ETAAS)

The operational characteristics of a novel poly(tetrafluoroethylene) (PTFE) bead material, granular Algoflon^®, used for separation and preconcentration of metal ions via adsorption of on-line generated non-charged metal complexes, were evaluated in a sequential injection (SI) system furnished with an external packed column and in a sequential injection lab-on-valve (SI-LOV) system. Employed for the determination of cadmium(II), complexed with diethyldithiophosphate (DDPA), and detection by electrothermal atomic absorption spectrometry (ETAAS), its performance was compared to that of a previously used material, Aldrich PTFE, which had demonstrated that PTFE was the most promising for solid-state pretreatments. By comparing the two materials, the Algoflon^® beads exhibited much higher sensitivity (1.6107 μg l⁻¹ versus 0.2956 μg l⁻¹ per integrated absorbance (s)), and better retention efficiency (82% versus 74%) and enrichment factor (20.8 versus 17.2), although a slightly smaller linear dynamic range (0.05-0.25 μg l⁻¹ versus 0.05-1.00 μg l⁻¹). Moreover, no flow resistance was encountered under the experimental conditions used. The results obtained on three standard reference materials were in good agreement with the certified values.     

Running buffers for determination of chromium(VI)/(III), cobalt(II) and zinc(II) in complex matrices by capillary electrophoresis with contactless conductivity detection

Complex matrices and rather high acidity in environmental samples are often the impelling challenges for the used running buffers of capillary electrophoresis. Twelve binary acid-base buffers were evaluated for separation of Cr(VI)/Cr(III), Co²⁺ and Zn²⁺ in a sample containing various salts by capillary electrophoresis with contactless conductivity detector. The malic acid (MA) systems including MA-His (histidine), MA-Arg (arginine) and MA-Tris (tris(hydroxymethyl)aminomethane) were selected as the candidates with powerful separation efficiency and good response sensitivity. In the MA-Tris buffer, optimization were further carried out in terms of the pH value and the concentration of MA, and the optimal conditions were obtained as 6 mM MA-Tris and 2 mM 18-crown-6 at pH 3.5. Furthermore, a real application was demonstrated by analyzing the plating rinse water (pH 0.8), in which the Ca²⁺, Na⁺, Cr(VI)/Cr(III), Co²⁺ and Zn²⁺ were all detected by adjusting at pH 3.5 with 5% (v/v) diluent ammonia. Both the cations, e.g., K⁺, Ca²⁺, Na⁺, Mg²⁺, and the common high concentration anions in the sample, e.g., Cl⁻, SO₄²⁻ and NO₃⁻ did not cause any disturbance to the concerned analytes.     

Direct analysis of environmental and biological samples for total mercury with comparison of sequential atomic absorption and fluorescence measurements from a single combustion event

A Direct Mercury Analyzer (DMA) based on sample combustion, concentration of mercury by amalgamation with gold, and cold vapor atomic absorption spectrometry (CVAAS) was coupled to a mercury-specific cold vapor atomic fluorescence spectrometer (CVAFS). The purpose was to evaluate combustion-AFS, a technique which is not commercially available, for low-level analysis of mercury in environmental and biological samples. The experimental setup allowed for comparison of dual measurements of mercury (AAS followed by AFS) for a single combustion event. The AFS instrument control program was modified to properly time capture of mercury from the DMA, avoiding deleterious combustion products from reaching its gold traps. Calibration was carried out using both aqueous solutions and solid reference materials. The absolute detection limits for mercury were 0.002 ng for AFS and 0.016 ng for AAS. Recoveries for reference materials ranged from 89% to 111%, and the precision was generally found to be <10% relative standard deviation (RSD). The two methods produced similar results for samples of hair, finger nails, coal, soil, leaves and food stuffs. However, for samples with mercury near the AAS detection limit (e.g., filter paper spotted with whole blood and segments of tree rings) the signal was still quantifiable with AFS, demonstrating the lower detection limit and greater sensitivity of AFS. This study shows that combustion-AFS is feasible for the direct analysis of low levels of mercury in solid samples that would otherwise require time-consuming and contamination-prone digestion.