Investigation of on-line coupling electrothermal atomic absorption spectrometry with flow injection sorption preconcentration using a knotted reactor for totally automatic determination of lead in water samples

A flow injection on-line sorption preconcentration electrothermal atomic absorption spectrometric system for fully automatic determination of lead in water was investigated. The discrete non-flow-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome for the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocarbamate complex was adsorbed on the inner walls of a knotted reactor made of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the eluate delivery tube, then the adsorbed analyte chelate was quantitatively eluted into a delivery tube with 50 μl of ethanol. An air flow was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transversely heated graphite tube atomizer, which was preheated to 80°C. With the use of the new FI manifold, the consumption of eluent was greatly reduced and dispersion was minimized. The adsorption efficiency was 58%, and the enhancement factor was 142 in the concentration range 0.01–0.05 μg l⁻¹ Pb at a sample loading rate of 6.8 ml min⁻¹ with 60 s preconcentration time. For the range 0.1–2.0 μg l⁻¹ of Pb a loading rate of 3.0 ml min⁻¹ and 30 s preconcentration time were chosen, resulting in an adsorption efficiency of 42% and an enhancement factor of 21, respectively. A detection limit (3σ) of 2.2 ng l⁻¹ of lead was obtained using a sample loading rate of 6.8 ml min⁻¹ and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 μg l⁻¹ Pb level with a loading rate of 6.8 ml min⁻¹ and 60 s preconcentration, and 2.9% at the 0.5 μg l⁻¹ Pb level with a 3.0 ml min⁻¹ loading rate and 30 s preconcentration. Efficient washing of the matrix from the reactor was critical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certified values.     

On-line precipitation–dissolution in knotted reactor for thermospray flame furnace AAS for determination of ultratrace cadmium

A simple, environmentally friendly, cost-effective and sensitive method was developed for the determination of trace cadmium in rice and water by using flow injection (FI) on-line precipitation–dissolution in a knotted reactor (KR) as a preconcentration scheme for thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The preconcentration was achieved by online merging the sample solution and the precipitating reagent in a KR and subsequently eluting the resultant precipitate of cadmium hydroxide with 1 mol/L HNO₃. The eluant was then introduced into TS-FF-AAS for the determination. A self-assembled FI system was employed to hyphenate the KR system with TS-FF-AAS. Under optimal chemical and instrumental conditions, a limit of detection of 0.04 μg/L and a sensitivity enrichment factor of 34 for cadmium was obtained with a total initial sample volume of 4 mL. The proposed method was applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with their certified values. Real rice samples and real water samples were also determined by the proposed method, with analytical results confirmed by inductively coupled plasma mass spectroscopy (ICP-MS).     

Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent

A fully automated procedure for the determination of ng l⁻¹ amounts of lead has been developed using flow injection (FI) online column preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. The interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn (50 μl) packed with Pb-02, and after washing the column with dilute nitric acid, air is introduced to remove all solution from the column and connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100°C, with 36 μl of ETDA solution (0.035 mol l⁻¹, pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and with a sample loading flow rate of 3 ml min⁻¹ and a 60 s preconcentration time, the enhancement factor was 77 and the throughput was 17 samples per hour. The relative standard deviation (n = 10) at the 300 ng l⁻¹ level was 2.7%, and the detection limit (3σ) was 0.4 ng l⁻¹. No interference from heavy metals was observed, but ions of Ba²⁺, Sr²⁺ and K⁺ were found to interfere when the concentration ratios of interferent to lead exceeded values of 2000, 20 000 and 200 000, respectively. Quantitative recovery of lead was achieved from sodium, magnesium, aluminum, lanthanum and heavy metal salt solutions. The high selectivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of high-purity reagents, semiconductors and other high-purity materials. Results are presented for the determination of lead in some high-purity reagents.     

Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP-FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0 ml min⁻¹ and a total preconcentration time of 180 s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26 μg l⁻¹ for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2 μg l⁻¹ Cr(VI), Co(II) and Ni(II), and 1 μg l⁻¹ Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.     

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.     

An on-line flow-injection microwave-assisted mineralization and a precipitation/dissolution system for the determination of molybdenum in blood serum and whole blood by electrothermal atomic absorption spectrometry

An on-line flow injection (FI) precipitation–dissolution system with microwave-assisted sample digestion has been developed for the electrothermal atomic absorption spectrometry (ETAAS) determination of trace or ultratrace amounts of molybdenum in human blood serum and whole blood samples. After the exposure of the sample to microwave radiation, the on-line precipitation of molybdenum was achieved by the merging-zone of a 0.5-ml plug of sample with a plug of potassium ferrocyanide, which were carried downstream with a solution of 0.5 mol l⁻¹ of HNO₃. The interfering effects of iron and copper were minimized by the introduction of a flow of a 5% (w/v) sodium potassium tartrate (for iron) and 2% (w/v) of thiourea (for copper and zinc) in a 5% (v/v) ammonia and 2% (v/v) ammonium chloride solution previous to the precipitation reaction. The reddish-brown precipitate of molybdenyl ferrocyanide was collected on the walls of a knotted reactor. The precipitate was dissolved with the introduction of 1 ml of a 3.0 mol l⁻¹ NaOH solution and the best performance in terms of detection limit and precision was achieved when a sub-sample of 140 μl was collected in a capillary of a sampling arm assembly, to introduce 20 μl volumes into the atomizer by means of positive displacement with air through a time-based injector. A detection limit (3σ) of 0.1 μg Mo l⁻¹ using an aqueous standard solution was obtained. The method is quantitative and is applied over the range 0.2–20.0 μg Mo l⁻¹. The precision of the method evaluated by ten replicate analyses of aqueous standard solutions containing 0.5 and 1.0 μg Mo l⁻¹ was 2.8 and 3.1% (relative standard deviation, RSD) (for n=5), respectively. Whereas, the precision evaluated by five replicate analysis of a serum and a whole blood sample were 3.3 and 3.8% RSD. An enrichment factor of ca. 3.5 was achieved with the introduction of 0.5 ml aqueous standard solutions at a sample flow rate of 1.0 ml min⁻¹. Recoveries of spiked molybdenum in blood serum and whole blood were in the ranges 96–102 and 94–98%, respectively. The results obtained for two human whole blood certified reference materials were in good agreement with the indicative values.     

On-line preconcentration and determination of cobalt by DPTH-gel chelating microcolumn and flow injection inductively coupled plasma atomic emission spectrometry

This paper reports the development of a new methodology for the determination of cobalt in biological samples by using a flow injection system with loaded DPTH-gel as solid phase to preconcentrate analytes. The procedure is based on the on-line preconcentration of cobalt on a microcolumn of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel). The trapped cobalt is then eluted with 1% tartaric acid and 1% citric acid (7.1 mL) and determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). The analytical figures of merit for the determination of cobalt are as follows: detection limit (3S), 8.5 ng mL^–1; precision (RSD), 5.8% for 100 ng mL^–1 of cobalt; enrichment factor, 13 (using 7.3 mL of sample); sampling frequency, 40 h^–1 using a 60-s preconcentration time. For a 120-s preconcentration time (14.6 mL of sample volume) a detection limit of 5.7 ng mL^–1, an RSD under 5% at 50 ng mL^–1, an enrichment factor of 25, and a sampling frequency of 24 h^–1 were reported. The precision and accuracy of the method were checked by analysis of biological certified reference materials.     

Preconcentration of inorganic antimony(III) in environmental samples by PSTH-Dowex microcolumn and determination by FI-ETAAS

A flow injection on-line sorption preconcentration system has been synchronously coupled to an electrothermal atomic absorption spectrometry (ETAAS) system for the selective determination of trace amounts of Sb(III) in water, soil and plant. The determination was achieved by selective complexation and sorption of Sb(III) with [1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydarzide (PSTH) immobilized on an anion-exchange resin (Dowex 1× 8-200)] at a wide range of pH, quantitative elution with 50 μl of 2 M HNO₃ and subsequent ETAAS detection. ETAAS determination of the analyte was performed in parallel with the preconcentration of the next sample. Using a preconcentration time of 60 s and a sample loading flow rate of 2.8 ml min⁻¹, an enhancement factor of 12 was obtained in comparison with direct injection of 50 μl aqueous solution, resulting in a sampling frequency of 31 samples h⁻¹. The detection limit (3 s) was 2 μg l⁻¹ and the precision was 3.1% (R.S.D.) for 11 replicate determinations at 10 μg l⁻¹. The accuracy of the proposed method was demonstrated by analyzing one certified sample and different spiked samples.     

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。     

Determination of trace metal ions via on-line separation and preconcentration by means of chelating Sepharose beads in a sequential injection lab-on-valve (SI-LOV) system coupled to electrothermal atomic absorption spectrometric detection

The analytical performance of an on-line sequential injection lab-on-valve (SI-LOV) system using chelating Sepharose beads as sorbent material for the determination of ultra-trace levels of Cd(II), Pb(II) and Ni(II) by electrothermal atomic absorption spectrometry (ETAAS) is described and discussed. The samples are adjusted to pH 5.0 on-line in the system for optimum operation. The target ions are adsorbed by chelation on the surface of the beads, contained in a 20 μl microcolumn within the LOV, and following elution by 50 μl 2 M nitric acid, the eluate is, as sandwiched by air segments, introduced into the ETAAS. Based on the consumption of 1.8 ml sample solution, retention efficiencies of 95, 75 and 90%, enrichment factors of 34, 27 and 32, and determination limits of 0.001, 0.07 and 0.02 μg l⁻¹ were obtained for Cd(II), Pb(II) and Ni(II), respectively. The beads can be used repeatedly for at least 20 times without decrease of performance, yet can be replaced at will if the circumstances should so dictate. The optimized procedural parameters showed that 12 samples per hour could be prepared and successfully analyzed. The results obtained for three standard reference materials agreed very well with the certified values.     

Use of 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel for automated preconcentration and selective determination of antimony(III) by flow-injection electrothermal atomic absorption spectrometry

Selective sorption of Sb(III) on a microcolumn packed with 1,5-bis(di-2-pyridyl)methylene thiocarbohydrazide immobilized on silica gel (DPTH-gel) has been used for determination of Sb(III). A flow-injection system comprising a microcolumn connected to the tip of the autosampler was used for preconcentration. The sorbed antimony was eluted with nitric acid directly into the graphite furnace and determined by AAS. The detection limit for antimony under the optimum conditions was 0.3 ng mL^–1. This procedure was used for determination of antimony in natural water, soil, vegetation, and a certified sample of a city waste incineration ash (BCR 176).     

流动注射壳聚糖在线微柱预富集电热原子吸收光谱法测定痕量Cr(VI)

以天然高分子材料壳聚糖作在线预富集柱填料,流动注射与电热原子光谱联用测定痕量Cr(VI)。采样体积5.80mL,采样频率22样/h,富集倍数51倍,线性范围0.02μg/L～0.12μg/L,该方法的检出限(3s,n=11)0.69ng/L,相对标准偏差5.1%(CCr(VI)=0.10μg/L,n=11)。将该方法用于环境水样、茶叶样品和头发样品中Cr(VI)的测定,结果满意。     

Titanium as a chemical modifier for the determination of cobalt in marine sediments

The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO₃)₂ was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO₃)₂ as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m₀=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g⁻¹ using no modifier and 0.3 μg g⁻¹ with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g⁻¹ Co was analyzed and the found value of 10.9±2.4 μg g⁻¹, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value.     

流动注射在线置换吸附预富集-火焰原子吸收联用技术测定痕量铅

研究了流动注射在线置换吸附预富集-火焰原子吸收(FAAS)联用技术测定复杂样品中痕量铅的方法。首先使ZnⅡ与二乙基二硫代氨基甲酸钠(DDTC)在线配合形成Zn-DDTC并预先吸附在香烟过滤嘴填充柱上,然后使含PbⅡ的标准溶液或样品溶液流经填充柱与Zn-DDTC发生置换反应而被填充柱富集。被吸附的分析物用乙醇定量洗脱至FAAS进行在线检测。此在线置换吸附预富集过程有效地消除了与DDTC的配合物稳定性较Zn-DDTC弱的共存金属离子的干扰。在样品流速为5.0mL/min和置换吸附预富集90s的条件下,得到铅的吸收信号的增感因子为33,检出限为2.0μg/L。浓度为100μg/L的铅标准溶液11次平行测定的精密度(RSD)为1.2%。本方法已应用于生物样品的分析。     

Silica-modified magnetic nanoparticles functionalized with cetylpyridinium bromide for the preconcentration of metals after complexation with 8-hydroxyquinoline

Magnetically driven separation technology has received considerable attention in recent decade for its great potential application. In this study, we investigate the application of silica-modified magnetite nanoparticles (NPs) coated with a cationic surfactant as adsorbent for microextraction and determination of trace amounts of Cu(II), Ni(II), Co(II), Cd(II), Pb(II) and Mn(II) from environmental water samples. The synthesized silica-coated NPs in combination with cetylpyridinium bromide have the ability to adsolubilize the metal ions after complexation with 8-hydroxyquinoline. The NPs bearing the target metals are easily separated from the aqueous solution by applying an external magnetic field and the complexed metals were desorbed using acidic methanol. The desorbed analytes are introduced into the graphite furnace of an atomic absorption spectrometer. The effect of pH, complexing agent, amount of cetylpyridinium bromide, microextraction time, desorption conditions, ionic strength on extraction efficiency of the metal ions are investigated and optimized. Under the optimized conditions, the detection limits for Cu(II), Ni(II), Co(II), Cd(II), Pb(II) and Mn(II) are 4.7, 9.1, 9.5, 2.3, 7.4 and 15.3 ng L⁻¹, respectively and the relative standard deviations (n = 6) are less than 3.6%. The accuracy of the method was evaluated by recovery measurements on the spiked samples and good recoveries (93-113%) with low RSDs were achieved.     

Determination of trace metals in urine with an on-line ultrasound-assisted digestion system combined with a flow-injection preconcentration manifold coupled to flame atomic absorption spectrometry

A flow analysis method with on-line sample digestion/minicolumn preconcentration/flame atomic absorption spectrometry is described for the determination of trace metals in urine. First, urine sample was on-line ultrasound-assisted digested exploiting the stopped-flow mode, and then the metals were preconcentrated passing the pre-treated sample through a minicolumn containing a chelating resin. A home-made minicolumn of commercially available imminodiacetic functional group resin, Chelite Che was used to preconcentrate trace metals (Cu, Fe, Mn and Ni) from urine. The proposed procedure allowed the determination of the metals with detection limits of 0.5, 1.1, 0.8 and 0.8 μg L⁻¹, for Cu, Fe, Mn and Ni, respectively. The precision based on replicate analysis was less than ±10.0%, and the enrichment factor obtained was between 21.3 (Mn) and 44.1 (Ni), for sample volumes between 2.5 and 5.0 mL, and an eluent volume of 110 μL. This procedure was applied for determination of metals in urine of workers exposed to welding fumes and urine of unexposed persons (urine control).     

Lead ultra-trace on-line preconcentration and determination using selective solid phase extraction and electrothermal atomic absorption spectrometry: applications in seawaters and biological samples

In this work, a new chelating resin [1,5-bis (2-pyridyl)-3-sulphophenyl methylene] thiocarbonohydrazide immobilised on aminopropyl-controlled pore glass (550 A; PSTH-cpg) was synthesised and packed in a microcolumn which replaced the sample tip of the autosampler arm. The system was applied to the preconcentration of lead. When microliters of 10% HNO3, which acts as elution agent, pass through the microcolumn, the preconcentrated Pb(II) is eluted and directly deposited in a tungsten-rhodium coated graphite tube. With the use of the separation and preconcentration step and the permanent modifiers, the analytical characteristics of the technique were improved. The proposed method has a linear calibration range from 0.012 to 10 ng ml(-1) of lead. At a sample frequency of 36 h(-1) with a 90 s preconcentration time, the enrichment factor was 20.5, the detection and determination limits were 0.012 and 0.14 ng ml(-1), respectively and the precision, expressed as relative standard deviation, was 3.2% (at 1 ng ml(-1)). Results from the determination of Pb in biological certified reference materials were in agreement with the certified values. Seawaters and other biological samples were analysed too.     

Use of modified rice husks as a natural solid adsorbent of trace metals: characterisation and development of an on-line preconcentration system for cadmium and lead determination by FAAS

The use of rice husks as an alternative adsorbent in an on-line preconcentration system for Cd (II) and Pb (II) determination by flame atomic absorption spectrometry (FAAS) is described. The potential of rice husks as a natural adsorbent was evaluated as a material modified with 0.75 mol l⁻¹ NaOH solution and in the unmodified form. For this task, several techniques such as spectroscopy and thermogravimetry were used for elucidation of possible functional groups responsible for the uptake of Cd (II) and Pb (II). Furthermore, based on adsorption studies and adsorption isotherms applied to the Langmüir model, it was possible to verify that modified rice husks present a higher adsorption capacity for both metals. After establishing this material as a promising natural adsorbent, it was used for on-line preconcentration of Cd (II) and Pb (II) metals. The multivariate optimisation of chemical and flow variables was performed by using a full factorial design (2⁴) including the following factors: preconcentration time, preconcentration flow rate, concentration and volume of eluent. The optimum pH values used for on-line preconcentration were taken from prior univariate experiments. Under optimised conditions for Cd (II) determination (4 min of preconcentration at a 6 ml min⁻¹ preconcentration flow rate, in which comprises 24 ml of preconcentration volume, 200 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent), the system achieved a detection limit of 1.14 μg l⁻¹ and an enrichment factor of 72.4. Similar conditions were used for Pb (II) determination (4 min of preconcentration, 6 ml min⁻¹ preconcentration flow rate, 300 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent) from which a detection limit of 14.1 μg l⁻¹ and enrichment factor of 46.0 were achieved. Also, rice husks have been shown to be a homogeneous and stable adsorbent in which more than 100 preconcentration/elution cycles provide a relative standard deviation (RSD) of less than 6.0% on the analytical signal. The satisfactory accuracy of the method developed was obtained by using spiked water samples (mineral water and lake water) and spiked red wine samples. These values were confirmed by electrothermal atomic absorption spectrometry (ETAAS). The certified reference material [pig kidney (CRM 186)] and the reference material [beech leaves (CRM 100)] were also used.     

On-line organoselenium interference removal for inorganic selenium species by flow injection coprecipitation preconcentration coupled with hydride generation atomic fluorescence spectrometry

The existence of dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in some environmental samples can cause serious interference on Se(IV) determination by hydride generation atomic fluorescence spectrometry (HG-AFS) due to their contribution on HG-response. A flow injection separation and preconcentration system coupled to HG-AFS was therefore developed by on-line coprecipitation in a knotted reactor (KR) for eliminating interference subjected from organoselenium. The sample, spiked with lanthanum nitrate, was merged with an ammonium buffer solution (pH 8.8), which promoted coprecipitation of Se(IV) and quantitative collection by 150 cm PTFE KR. DMSe and DMDSe, however, were unretained and expelled from the KR. An air flow was introduced to remove the residual solution from the KR, then a 1.2 mol l⁻¹ HCl was pumped to dissolve the precipitates and merge with KBH₄ solution for HG-AFS detection. The interference of DMSe and DMDSe on the Se(IV) determination by conventional HG-AFS and its elimination by the developed separation and preconcentration system were evaluated. With optimal experimental conditions and with a sample consumption of 12.0 ml, an enhancement factor of 18 was obtained at a sample frequency of 24 h⁻¹. The limit of detection was 0.014 μg l⁻¹ and the precision (R.S.D.) for 11 replicate measurements of 1.0 μg l⁻¹ Se(IV) was 2.5%. The developed method was successfully applied to the determination of inorganic selenium species in a variety of natural water samples.     

Determination of tellurium at ultra-trace levels in drinking water by on-line solid phase extraction coupled to graphite furnace atomic absorption spectrometer

In this paper, two time-based flow injection (FI) separation pre-concentration systems coupled to graphite furnace atomic absorption spectrometry (GFAAS) for tellurium determination are studied and compared. The first alternative involves the pre-concentration of the analyte onto Dowex 1X8 employed as packaging material of a micro-column inserted in the flow system. The second set-up is based on the co-precipitation of tellurium with La(OH)₃ followed by retention onto XAD resins. Both systems are compared in terms of limit of detection, linear range, RSD%, sample throughput, micro-columns lifetime and aptitude for fully automatic operation.