Preconcentration and determination of trace metals by flow injection micelle-mediated extraction using flame atomic absorption spectrometry

Micelle-mediated extraction/preconcentration is incorporated on-line into a flow injection system used to determine low levels of Cd(II), Co(II), Cu(II), Mn(II), Ni(II), Pb(II) and Zn(II) present in various samples. The analyte is complexed with HBDAP (N,N′-bis(2-hydroxy-5-bromo-benzyl)1,2-diaminopropane). Under optimal conditions, a solution of 30% (m/v) NaCl and a sample solution containing 2.5 mL of 1% (m/v) sodium dodecyl sulfate (SDS), 0.5 mL of 1.8 × 10⁻³ M HBDAP and 2.5 mL of pH 8.5 borate buffer solution in 25 mL were pumped through the cotton filled mini-column; onto which the surfactant-rich phase containing the complex is collected. A solution of 0.5 M HNO₃ in 50% acetone is used as the eluent. The limits of detection are (ng mL⁻¹) Cd = 0.39, Cu = 3.2, Co = 7.5, Mn = 3.0, Ni = 3.4, Pb = 17.9 and Zn = 0.89 if the sample is allowed to flow for 30 s, but improved for extended preconcentration periods. Analysis of liquid and solid reference materials showed good agreement with the certified values. Complex formation constants between HBDAP and these metal ions were also determined potentiometrically.     

Calibration by the gradient ratio-standard addition method in flow injection flame atomic absorption spectrometry

A calibration method has been developed which is realised in the flow injection analysis (FIA) by the gradient technique. According to this method two transient peaks, one for a sample and the other for a sample with standard addition, are recorded and compared point by point in the entire defined time range. The analytical result is estimated on the basis of information gained about the local analyte concentrations in the sample zone. The method allows the results to be reliable when both the non-linear calibration dependence and the interference effect occur. As an example, calcium in synthetic samples containing silicon, phosphate, aluminium, vanadium and titanium, and also in iron ore sample, were determined by flame atomic absorption spectrometry (FAAS). It has been proved, that the method can be effective in overcoming even extremely strong interferences, providing analytical results with average accuracy equal to ca. 5% and with precision 2–3 times inferior to that obtained by conventional FI calibration.     

Application of pyridylazo and thiazolylazo reagents in flow injection preconcentration systems for determination of metals

Pyridylazo and thiazolylazo reagents are synthetic dyes widely used in analytical chemistry. These reagents are also very attractive for use in preconcentration systems. This paper covers the application of pyridylazo and thiazolylazo reagents in flow injection systems for the determination of metals. The article discusses flow injection preconcentration systems with solid-phase extraction, precipitation and cloud point extraction. The use of pyridylazo and thiazolylazo reagents in flow injection detection systems is also presented. The relative advantages and drawbacks of these systems are discussed. The application of pyridylazo and thiazolylazo reagents in new systems is presented in the concluding part of this review article.     

Coupling of flow injection wetting-film extraction without segmentation and phase separation to flame atomic absorption spectrometry for the determination of trace copper in water samples

A flow injection wetting-film extraction system without segmentor and phase separator has been coupled to flame atomic absorption spectrometry for the determination of trace copper. Isobutyl methyl ketone (MIBK) was selected as coating solvent and 8-hydroxyquinoline (oxine) as the chelating reagent. By switching of a 8-channel valve and alternative initiation of two peristaltic pumps, MIBK, sample solution containing copper chelate of oxine, and air-segment sandwiched eluting solution (1.0 mol l⁻¹ nitric acid) were sequentially aspirated into an extraction coil made of PTFE tubing of 360 cm length and 0.5 mm i.d. The formation of organic film in the wall of the extraction coil, extraction of the copper chelate into the organic film and back-extraction of the analyte into the eluting solution occurred consecutively when these zones aspirated into the extraction coil were propelled down the extraction coil by a carrier solution at a flow rate of 2 ml min⁻¹. After leaving the extraction coil, the concentrated zone was transported to the nebulizer at its free uptake rate for atomization. Under the optimized conditions, an enrichment factor of 43 and a detection limit of 0.2 μg l⁻¹ copper were achieved at a sample throughput rate of 30 h⁻¹. Eleven determinations of a standard copper solution of 60 μg l⁻¹ gave a relative standard deviation of 1.5%. Foreign ions possibly present in tap water and natural water did not interfere with the copper determination. The developed method has been successfully used to the determination of copper content of tap water and river water.     

Separation and preconcentration by flow injection coupled to tungsten coil electrothermal atomic absorption spectrometry

A flow injection system coupled to a tungsten coil electrothermal atomizer has been developed for on-line separation and preconcentration, using lead as a model element. The system utilizes three-way solenoid valves for sampling, buffering, washing and reconditioning solution management, and the resin column is inserted in the tip of the autosampler arm of a Varian GTA-96. The solenoid valves and tungsten coil power supply were controlled by a computer program written in Visual Basic, interfaced with the built-in Varian software. The system performance was tested by loading the resin column with the sample flowing at 3 ml min⁻¹ for 60 s. Elution was performed automatically by sampling 20 μl of the eluent from a sample cup of the autosampler, and this aliquot was delivered into a 150 W tungsten coil. With Chelex-100 resin, the separation of concomitants was tested with lead in the presence of as much as 1000 mg l⁻¹ of Ca, Mg, Na or K. The model system presented an enrichment factor of 64 at a sampling rate of 30 samples per hour.     

在线还原富集火焰原子吸收光谱法测定环境水样中Cr(Ⅲ)和Cr(Ⅵ)的形态

采用单阀双阳离子交换树脂微柱并联，设计了双路采样逆向洗脱在线分离富集系统，该系统与原子吸收测量技术相结合，实现了在线分离富集-火焰原子吸收光谱法同时测定水中Cr(Ⅲ)和Cr(Ⅵ)，富集1min时，分析速度为60样/h，测定Cr(Ⅲ)和Cr(Ⅵ)的特征浓度分别为6．08μg/L和11．58μg/L(相当于1％吸收)，线性范围分别为0～1．0μg/mL和0～2．0μg/mL，对质量浓度为100μg/L的Cr(Ⅲ)和Cr(Ⅵ)测定的相对标准偏差分别为2．9％和3．0％、检出限分别为8．70和10．8μg/L。该法对实际水样加标回收率在94．5％～104．3％之间。     

Extension of the dynamic range of flame atomic absorption spectrometry using flow injection analysis with variable-volume dilution chambers

A simple and inexpensive procedure is proposed for the extension of the dynamic range of flame atomic absorption spectrometry measurements using on-line dilution. The proposed methodology is based on the use of a manifold with two coupled dilution chambers and a zone injection system. The samples are prediluted in a closed system which includes a variable-volume mixing chamber (10–120 ml) and two injection valves. The samples are injected through one of these valves, and the other is employed to take 100 μl of prediluted samples which are then passed through a new dilution chamber (volume 1–10 ml) and aspirated by the nebulizer of the instrument. A third injection valve mounted in the last part of the manifold is used for the direct injection of diluted standard solutions. Various dilution factors are obtained, ranging from 2 to 130 000 times, thus extending the analytical range of copper determination to more than 100 000 mg l⁻¹.     

Solid phase extraction preconcentration of cobalt and nickel with 5,7-dichloroquinone-8-ol embedded styrene-ethylene glycol dimethacrylate polymer particles and determination by flame atomic absorption spectrometry (FAAS)

This article explores the synthesis of styrene-divinyl benzene (DVB)/ethylene glycol dimethacrylate (EGDMA) polymers embedded with quinoline-8-ol (Q) or its dihalo derivatives by thermal means in the presence and absence of 4-vinyl pyridine (VP). The above-synthesized polymers were found to enrich cobalt and nickel present in admixtures. Of these, 5,7-dichloroquinoline-8-ol (DCQ) embedded styrene-EGDMA polymer particles enrich cobalt and nickel quantitatively from dilute aqueous solutions within 5 min of preconcentration time. Styrene-EGDMA, DCQ embedded styrene-EGDMA particles obtained by bulk polymerization and cobalt/nickel bonded polymers were characterized by FTIR, thermogravimetric analysis (TGA), elemental analysis and surface area studies. The use of these polymer particles obtained by bulk polymerization for the solid phase extractive preconcentration of cobalt and nickel was investigated in detail and explores the possibility of employing this procedure for the analysis of cobalt and nickel in soil and sediment samples using a simple, low cost and readily available flame atomic absorption spectrometric instrument was explored.     

A novel fiber-packed column for on-line preconcentration and speciation analysis of chromium in drinking water with flame atomic absorption spectrometry

A novel on-line preconcentration and determination system based on a fiber-packed column was developed for speciation analysis of Cr in drinking water samples prior to its determination by flame atomic absorption spectrometry (FAAS). All variables involved in the development of the preconcentration method including, pH, eluent type, sample and eluent flow rates, interfering effects, etc., were studied in order to achieve the best analytical performance. A preconcentration factor of 32 was obtained for Cr(VI) and Cr(III). The levels of Cr(III) species were calculated by difference of total Cr and Cr(VI) levels. Total Cr was determined after oxidation of Cr(III) to Cr(VI) with hydrogen peroxide. The calibration graph was linear with a correlation coefficient of 0.999 at levels near the detection limit and up to at least 50 μg L⁻¹. The relative standard deviation (R.S.D.) was 4.3% (C = 5 μg L⁻¹ Cr(VI), n = 10, sample volume = 25 mL). The limit of detection (LOD) for both Cr(III) and Cr(VI) species was 0.3 μg L⁻¹. Verification of the accuracy was carried out by the analysis of a standard reference material (NIST SRM 1643e “Trace elements in natural water”). The method was successfully applied to the determination of Cr(III) and Cr(VI) species in drinking water samples.     

Peat as a natural solid-phase for copper preconcentration and determination in a multicommuted flow system coupled to flame atomic absorption spectrometry

The physical and chemical characteristics of peat were assessed through measurement of pH, percentage of organic matter, cationic exchange capacity (CEC), elemental analysis, infrared spectroscopy and quantitative analysis of metals by ICP OES. Despite the material showed to be very acid in view of the percentage of organic matter, its CEC was significant, showing potential for retention of metal ions. This characteristic was exploited by coupling a peat mini-column to a flow system based on the multicommutation approach for the in-line copper concentration prior to flame atomic absorption spectrometric determination. Cu(II) ions were adsorbed at pH 4.5 and eluted with 0.50 mol L⁻¹ HNO₃. The influence of chemical and hydrodynamic parameters, such as sample pH, buffer concentration, eluent type and concentration, sample flow-rate and preconcentration time were investigated. Under the optimized conditions, a linear response was observed between 16 and 100 μg L⁻¹, with a detection limit estimated as 3 μg L⁻¹ at the 99.7% confidence level and an enrichment factor of 16. The relative standard deviation was estimated as 3.3% (n = 20). The mini-column was used for at least 100 sampling cycles without significant variation in the analytical response. Recoveries from copper spiked to lake water or groundwater as well as concentrates used in hemodialysis were in the 97.3-111% range. The results obtained for copper determination in these samples agreed with those achieved by graphite furnace atomic absorption spectrometry (GFAAS) at the 95% confidence level.     

Lead preconcentration with flow injection for flame atomic absorption spectrometry

The flow-injecton preconcentration of lead with immobilised reagents under a variety of conditions is discussed. Timed sample loading and matrix removal without passing the matrix to the nebuliser were achieved simply with one valve. Reagent consumption and calibration time were reduced by the addition of further valves. A system design incorporating control of the timing of operations by a commercial autosample is described. The effects of pH and interferent ions were examined. Water samples were analysed against aqueous standards and as standard additions solutions. For an analysis time of about 3 min a preconcentration factor of about 40 was obtained for both peak height and area measurements. Detection limits of down to 1.4 ml^?1 were obtained.     

An ion-exchange method for speciation of antimony by flow injection electrothermal atomic absorption spectrometry

In this work, a simple preconcentration system, achieved by replacing the sample tip of the autosampler arm by a micro-column packed with Amberlite IRA-910 or silica gel chelating resin functionalised with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel), is developed for the determination of Sb(V) and total antimony, respectively. Different factors including pH of sample solution, ionic strength, concentration and volume of eluent, sample flow rate, sample loading time and matrix effects for preconcentration were investigated. The method has been applied to the determination of antimony species in different samples.     

Rapid on-line sample dissolution assisted by focused microwave radiation for silicate analysis employing flame atomic absorption spectrometry: iron determination

An on-line automated flow injection system with microwave-assisted sample digestion was used to perform silicate rock dissolution in acid medium for iron determination. For this purpose, a continuous flow system was built up by using an automatic flow injection analysis (FIA) system coupled to a flame atomic absorption spectrometer (FAAS), including a focused microwave oven unit. Inside the microwave cavity was inserted a polytetrafluoroethylene (PTFE) reactor coil (300 cm length and 0.8 mm i.d.) where the dissolution takes place. Chemical and flow variables as well as iron determination parameters were studied. In the flow system, a slurry of the rock sample (50 mg in 200 ml of acid mixture HF+HCl+HNO₃) is pumped through the reaction coil and the microwaves are turned on. After elapsed the time required to complete the sample dissolution, the mixture is pumped again in order to fill the sampling loop (500 μl). Then, by changing the valve position, a water carrier stream pushes the sample solution through the flame atomic absorption spectrometer nebulizer. To achieve an accurate determination of the rock certified materials, the slurry sample was irradiated during 210 s at 90 W power. Working in that condition, a detection limit of 0.80 μg ml⁻¹ (which corresponds to an Fe₂O₃ content of 0.46%) and an analytical throughput of 10 h⁻¹ were achieved. The relative standard deviation (R.S.D.) of the method varied between 1 and 11% when applied to the rock certified materials.     

流动注射在线萃取色谱分离原子吸收光谱法测定痕量铂

研究了流动注射在线分离富集原子吸收光谱法测定痕量铂的方法。以自制的GDX501-TBP萃取树脂为微型分离柱，在优化后的分离富集条件下，进样时间为60s，洗脱时间为45s。在线分离测定时间为3min，方法检出限为0．25μg/L，线性范围10—600μg/L，加标回收率为97．8％-103．6％，相对标准偏差3．49％-4．25％。方法已用于矿物管理样中铂的测定。     

Dithizone immobilized silica gel on-line preconcentration of trace copper with detection by flame atomic absorption spectrometry

A novel adsorbent-silica gel bound dithizone (H₂Dz-SG) was prepared and used as solid-phase extraction of copper from complex matrix. The H₂Dz-SG is investigated by means of FT-IR spectra and the SEM images, demonstrating the bonding of dithizone. The H₂Dz-SG quantitatively adsorb copper ions, and the retained copper is afterwards collected by elution of 10% (v/v) nitric acid. An on-line flow injection solid-phase extraction procedure was developed for trace copper separation and preconcentration with detection by flame atomic spectrometry. By loading 5.4 mL of sample solution, a liner range of 0.5-120 μg L⁻¹, an enrichment factor of 42.6, a detection limit of 0.2 μg L⁻¹ and a precision of 1.7% RSD at the 40 μg L⁻¹ level (n = 11) were obtained, along with a sampling frequency of 47 h⁻¹. The dynamic sorption capacity of H₂Dz-SG to Cu²⁺ was 0.76 mg g⁻¹. The accuracy of the proposed procedure was evaluated by determination of copper in reference water sample. The potential applications of the procedure for extraction of trace copper were successfully accomplished in water samples (tap, rain, snow, sea and river). The spiking recoveries within 91-107% are achieved.     

Determination of iron and copper in food samples by flow injection cloud point extraction flame atomic absorption spectrometry

In this study, flow injection-cloud point extraction (FI-CPE) of iron and copper in food samples by flame atomic absorption spectrometric determination was described. Triton X-114 non-ionic surfactant and Eriochrome Cyanine R (ECR) have been used as an extraction medium and a chelating agent, respectively. The amounts of Triton X-114, ECR and the pH value necessary for extraction were carefully optimized. In addition, several parameters of the FI-CPE system, including sample loading rate, column dimension, type of packing material, eluent flow rate were investigated and analytical characteristics of the method were evaluated. Under optimum conditions, detection limits of 0.33 ng/mL and 0.57 ng/mL and quantification limits of 1.1 ng/mL and 1.9 ng/mL for iron and copper along with enrichment factors of 141 and 99 were obtained, respectively. The calibration was linear over the range 1.5-25 ng/mL and 1.0-35 ng/mL for iron and copper, respectively. The proposed CPE technique has been successfully applied for the determination of iron and copper ions in certified reference materials (NCS DC 73349—bush, branches and leaves; and TM-23.2—fortified water), water samples (mineral and sea water) and food samples (vegetables, bread and hazelnut) with high efficiency.     

On-line coupling of flow injection displacement sorption preconcentration to high-performance liquid chromatography for speciation analysis of mercury in seafood

A simple and cost-effective method for speciation analysis of trace mercury in seafood was developed by on-line coupling flow injection microcolumn displacement sorption preconcentration to high-performance liquid chromatography (HPLC) with UV detection. The methodology involved the presorption of the Cu-PDC (pyrrolidine dithiocarbamate) chelate onto a microcolumn packed with a cigarette filter sorbent, simultaneous preconcentration of Hg(II), methylmercury (MeHg), ethylmercury (EtHg), and phenylmercury (PhHg) onto the microcolumn through a displacement reaction with the presorbed Cu-PDC, and their subsequent elution from the microcolumn for on-line HPLC separation. Interferences from heavy metal ions with lower stability of their PDC chelates relative to Cu-PDC were minimized without the need of any masking agents. With the consumption of 4.0 ml of sample solution, the enrichment factors were about 80. The detection limits were 10-25 ng g(-1) (as Hg) in fresh tissue. Precision (R.S.D. (%), n = 5) ranged from 2 to 3% at the 500 microg l(-1) (as Hg) level. The developed technique was validated by analyzing a certified reference material (DORM-2, dogfish-muscle), and was shown to be useful for mercury speciation in real seafood samples.     

On-line preconcentration and determination of cobalt by chelating microcolumns and flow injection atomic spectrometry

A simple and sensitive flow injection analysis-atomic absorption spectrometric procedure is described for the determination of cobalt. The method is based upon on-line preconcentration of cobalt on a microcolumn of 2-nitroso-1-naphthol immobilized on surfactant coated alumina. The trapped cobalt is then eluted with ethanol (250 μl) and determined by flame atomic absorption spectrometry. The analytical figures of merit for the determination of cobalt are as follows: detection limit (3 S), 0.02 ng ml⁻¹; precision (RSD), 2.8% for 20 ng ml⁻¹ and 1.7% for 70 ng ml⁻¹ of cobalt; enrichment factor, 125 (using 25 ml of sample). The method has been applied to the determination of cobalt in water samples, vitamin B₁₂ and B-complex ampoules and accuracy was assessed through recovery experiment and independent analysis by furnace AAS.     

Determination of gold in ore by flame atomic absorption spectrometry with flow-injection on-line sorbent extraction preconcentration

Gold in ores was determined by flame atomic absorption spectrometry following on-line preconcentration by sorbent extraction in a flow-injection system. The medium polarity adsorption resin Amberlite XAD-8 packed in a 220-μl micro-column was used to collect gold(III) from hydrochloric acid sample solutions for 40 s at 7.6 ml/min. Ethanol was used to elute the adsorbed analytes into the nebulizer. Optimization studies were made on sample loading rate, elution rate and sample acidity. Some possible interferences on the determination are discussed. A 35-fold enrichment was achieved at a sampling frequency of 60 h^?1 and with an RSD of 1.4%. The detection limit (3σ) and 2 μg l^?1. Results for gold in ore samples showed good agreement with those obtained using activated carbon adsorption preconcentration. The recoveries were 97–108%.     

Flow injection on-line dilution for flame atomic absorption spectrometry by micro-sample introduction and dispersion using syringe pumps

A robust flow injection (FI) on-line dilution system based on micro-sample introduction was developed for flame atomic absorption spectrometry (FAAS). Two computer programmed and stepper-motor driven syringe pumps were used for the precise and reproducible sample metering in micro-liters and carrier delivery. Factors, which might influence the performance of the system, such as sample matrix and carryover, were investigated. No inferior effects were observed with various matrices including 10% glycerol. Sample carryover effects were less than 0.4%, tested by analyzing a blank and a sample alternately. Dilution factors were decided and keyed in manually. The system was calibrated using a set of concentrated standard solutions for a given dilution factor. At a sampling frequency of 60 h⁻¹, precisions were better than 2% R.S.D. (n=40) for dilution factors of 10-2000. The long-term stability of the system was examined by continuously running the system for a whole working day, and a precision of 2.6% R.S.D. (n=345) was obtained at a dilution factor of 1000. The system was verified by analyzing a standard copper alloy with a certified concentration of 57.4% Cu, resulting in a measurement solution with 574 mg l⁻¹ Cu.