Use of Nb(2)O(5)-SiO(2) in an automated on-line preconcentration system for determination of copper and cadmium by FAAS

A procedure for the determination of trace level of copper(II) and cadmium(II) by FAAS using an on-line preconcentration system has been proposed. In this system, copper and cadmium ions were adsorbed onto a minicolumn packed with silica gel modified with niobium(V) oxide (Nb₂O₅-SiO₂), followed by nitric acid elution in reverse mode and determination on-line by flame atomic absorption spectrometry (AAS) without interference of the matrix. Chemical and flow variables as well as concomitant ions were studied in the developed procedure. The enrichment factor for copper(II) and cadmium(II) was 34.2 and 33.0, respectively, using a preconcentration time of 2 min. The limit of detection for copper(II) and cadmium(II) was 0.4, and 0.1 μg l⁻¹, respectively. The precision of the method, evaluated as the relative standard deviation in solutions containing 15 μg l⁻¹ of copper and 10 μg l⁻¹ of cadmium, by analyzing a series of seven replicates, was 1.8 and 1.6%, respectively. The accuracy was assessed through recovery experiments of certified material and water samples.     

Synthesis and application of a functionalized resin in on-line system for copper preconcentration and determination in foods by flame atomic absorption spectrometry

An on-line system for preconcentration and determination of copper at μg l⁻¹ level by flame atomic absorption spectrometry (FAAS) is proposed. Amberlite XAD-2 functionalized with 3,4-dihydroxybenzoic acid packed in a minicolumn was used as sorbent. Copper(II) ions were sorbed in the minicolumn, from which it could be eluted by hydrochloric acid solution directly to the nebulizer-burner system of the FAAS. Eluent solution was carried by water at a flow rate of 5.00 ml min⁻¹. Signals were measured as peak height by using an instrument software. Achieved sampling rate was 27 samples per hour. Analytical parameters were evaluated and the results demonstrated that copper can be determined, with acetate buffer to adjust the sample pH at 6.0, preconcentration time of 120 s and a sample flow rate of 6.50 ml min⁻¹. The desorption was carried out with 30 μl of a 1.0 mol l⁻¹ hydrochloric acid solution. An enrichment factor of 33 in 13.00 ml of sample (120 s preconcentration time) was achieved by using the time-based technique. The detection limit (DL) (3 s) was 0.27 μg l⁻¹ and the precision (assessed as the relative standard deviation) reached values of 5.7-1.1% in copper solutions of 5.00 to 50.00 μg l⁻¹ concentration, respectively. The accuracy of procedure was confirmed by copper determination in certified reference materials. Recoveries of spike additions (1.0 or 2.0 μg g⁻¹) to food samples were quantitative (90.0-110.0%). These results proved also that the procedure is not affected by matrix interference and can be applied satisfactorily for copper determination in rice flour and starch samples.     

Synthesis and application of a functionalized resin for flow injection/F AAS copper determination in waters

This paper reports the development of a new strategy for low-level determination of copper in water samples by using a flow-injection system coupled to solid-phase extraction (SPE) using flame atomic absorption spectrometry (F AAS) as detector. In order to preconcentrate copper from samples, a minicolumn packed with a styrene-divinylbenzene resin functionalized with (S)-2-[hydroxy-bis-(4-vinyl-phenyl)-methyl]-pyrrolidine-1-carboxylic acid ethyl ester was used and the synthesis procedure is described. System operation is based on the on-line retention of Cu(II) ions at pH 9.0 ± 0.2 in a such minicolumn with posterior analyte elution with 2 mol l⁻¹ HCl directly to the F AAS nebulizer. The influence of several chemical (sample pH, buffer concentration, HCl eluent concentration and effect of the ionic strength) and flow (sample and eluent flow rates and preconcentration time) variables that could affect the performance of this system were investigated as well as the possible interferents. At optimized conditions, for 2 min of preconcentration time (13.2 ml of sample volume), the system achieved a detection limit of 1.1 μg l⁻¹, a R.S.D. 1% at 20 μg g l⁻¹ and an analytical throughput of 25 h⁻¹, whereas for 4 min of preconcentration time (26.4 ml of sample volume), a detection limit of 0.93 μg l⁻¹, a R.S.D. 5.3% at 5 μg l⁻¹ and a sampling frequency of 13 h⁻¹ were reported.     

On-line solid phase extraction system using 1,10-phenanthroline immobilized on surfactant coated alumina for the flame atomic absorption spectrometric determination of copper and cadmium

An on-line solid phase extraction (SPE) preconcentration system coupled to flame atomic absorption spectrometer (FAAS) was developed for determination of copper and cadmium at μg L⁻¹ level. The method is based on the on-line retention of copper and cadmium on a microcolumn of alumina modified with sodium dodecyl sulfate (SDS) and 1,10-phenanthroline and subsequent elution with ethanol and determination by FAAS. The effect of chemical and flow variables that could affect the performance of the system was investigated. The relative standard deviation (n = 6) at 20 μg L⁻¹ level for copper and cadmium were 1.4 and 2.2% and the corresponding limits of detection (based on 3σ) were 0.04 and 0.14 μg L⁻¹, respectively. The method was successfully applied to determination of copper and cadmium in human hair and water samples.     

Application of silica gel organofunctionalized with 3(1-imidazolyl)propyl in an on-line preconcentration system for the determination of copper by FAAS

This study presents a new procedure for the determination of trace levels of copper(II) in an aqueous matrix, through flow injection (FI) on-line preconcentration with a minicolumn packed with silica gel modified with 3(1-imidazolyl)propyl groups. After the preconcentration stage, the analyte was eluted with a HNO₃ solution and determined by flame atomic absorption spectrometry (FAAS). The measurements of the analytical signals were carried out as peak area and peak height with the objective of evaluating the most appropriate absorption measurement for the proposed method. Four procedures to calculate the experimental enrichment factor (EF) were also studied. For a preconcentration time of 90 s the enrichment factors found in this study varied between 19.5-25.8 and 36.2-42.2 for peak area and peak height, respectively. The precision of the proposed method was calculated for a solution containing 20 μg l⁻¹ of Cu(II), when 11.2 ml of solution was preconcentrated (n=7), and their respective relative standard deviation (R.S.D.) values were 1.2 and 1.4% for peak area and peak height, respectively. The detection limits obtained were 0.4 and 0.2 μg l⁻¹ of Cu(II) for peak area and peak height, respectively, with a preconcentration time of 90 s. The on-line preconcentration system accuracy was evaluated through a recovery test on the aqueous samples and analysis of a certified material.     

Synthesis of amberlite XAD-2-PC resin for preconcentration and determination of trace elements in food samples by flame atomic absorption spectrometry

A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through –N=C– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as packing for the minicolumn in an on-line system preconcentration system for cadmium, cobalt, copper and nickel determination. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer–burner system of the flame atomic absorption spectrometer (FAAS). Elution of all metals from minicolumn can be made with 0.50 mol L^− 1 HCl or HNO₃. The enrichment factors obtained were 16 (Cd), 24 (Co), 15 (Cu) and 19 (Ni), for 60 s preconcentration time, and 39 (Cd), 69 (Co), 36 (Cu) and 41 (Ni), if used 180 s preconcentration time. Under the optimum conditions, the proposed procedure allowed the determination of cadmium, cobalt, copper and nickel with detection limits of 0.31, 0.32, 0.39 and 1.64 μg L^− 1, respectively, when used preconcentration periods of 180 s. The accuracy of the developed procedure was sufficient and evaluated by the analysis of the certified reference materials NIST 1515 apple leaves and NIST 1570a spinach leaves. The method was applied to the analysis of food samples (spinach, black tea and rice flour).     

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.     

Gallium trace on-line preconcentration/separation and determination using a polyurethane foam mini-column and flame atomic absorption spectrometry. Application in aluminum alloys, natural waters and urine

A sensitive and selective flow injection time-based method for on-line preconcentration/separation and determination of gallium by flame atomic absorption spectrometry at trace levels was developed. The on-line formed gallium chloride complex is sorbed onto a polyether-type polyurethane foam mini-column, followed by on-line quantitative elution with isobutyl methyl ketone and direct introduction into the flame pneumatic nebulizer of the atomic absorption spectrometer. All chemical and flow variables of the system as well as the possible interferences were studied. The manner of strong HCl solutions propulsion was investigated and established using a combination of two displacement bottles. For 90 s preconcentration time, a sample frequency of 28 h⁻¹, an enhancement factor of 40, a detection limit of 6 μg l⁻¹ and a precision expressed as relative standard deviation (s_r) of 3.3% (at 1.00 mg l⁻¹) were achieved. The calibration curve is linear over the concentration range 0.02-3.00 mg l⁻¹. The accuracy of the developed method was sufficient and evaluated by the analysis of a silicon-aluminum alloy standard reference material. Finally, it was successfully applied to gallium determination in commercial aluminum alloys, natural waters and urine.     

Amberlite XAD-2 functionalized with 2-aminothiophenol as a new sorbent for on-line preconcentration of cadmium and copper

A new functionalized resin has been applied in an on-line preconcentration system for copper and cadmium determination. Amberlite XAD-2 was functionalized by coupling it to 2-aminothiophenol (AT-XAD) by means of an NN spacer. This resin was packed in a minicolumn and used as sorbent in the on-line system. Metal ions were sorbed in the minicolumn, from which it could be eluted directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). Elution of Cd(II) and Cu(II) from minicolumn can be made with 0.50 mol l⁻¹ HCl or HNO₃. The enrichment factors obtained were 28 (Cd) and 14 (Cu), for 60 s preconcentration time, and 74 (Cd) and 35 (Cu), if used 180 s preconcentration time. The proposed procedure allowed the determination of cadmium and copper with detection limits of 0.14 and 0.54 μg l⁻¹, respectively, when used preconcentration periods of 180 s. The effects of foreign ions on the adsorption of these metal ions are reported. The validation of the procedure was carried out by analysis of certified reference material. This procedure was applied to cadmium and copper determination in natural, drink and tap water samples.     

Flow system with in-line separation/preconcentration coupled to graphite furnace atomic absorption spectrometry with W-Rh permanent modifier for copper determination in seawater

A flow system was coupled to a graphite furnace with a platform coated with tungsten-rhodium permanent chemical modifier for in-line separation and preconcentration of copper by employing a minicolumn loaded with 1-(2-tiazolylazo)-2-naphthol (TAN) immobilized on C₁₈-bonded silica fixed in the tip of the autosampler arm. Elution was made by sampling 35 μl of 0.50 mol l⁻¹ HCl with further delivering into a coated platform. Remarkable improvements in both selectivity and sensitivity were observed. Copper(II) was effectively separated from solutions containing up to 20 g l⁻¹ Na⁺; 10 g l⁻¹ K⁺, Ca²⁺ and Mg²⁺; 1.0 g l⁻¹ Fe³⁺ and Zn²⁺. For a sample flowing at 3.0 ml min⁻¹ and a loading of 60 s, the detection limit was estimated as 5 ng l⁻¹ Cu(II) at the 99.7% confidence level, and an enrichment factor of 33 was calculated. Coefficient of variation was estimated as 4% for a 0.30 μg l⁻¹ copper solution (n=20). The W-Rh permanent chemical modifier was used to improve system stability, analytical performance and atomizer lifetime. More than 1500 firings were carried out with the same atomizer without significant variations in sensitivity and precision. On account of the reagent immobilization, its consumption was lower than 0.2 μg per determination. In addition, TAN purification was unnecessary.     

An on-line cloud point extraction system for flame atomic absorption spectrometric determination of trace manganese in food samples

The development of an on-line preconcentration system with cloud point extraction for the determination of manganese is described. The system was used to determine manganese levels in food samples using flame atomic absorption spectrometry (FAAS). All steps of the cloud point extraction procedure were performed on-line, from the mixing of reagents to detection. The manganese ions are complexed in a mixture of the reagent 2-[2′-(6-methyl-benzothiazolylazo)]-4-bromophenol (Me-BTABr) and Triton X-114. The components are retained on a minicolumn and then desorbed with eluent acid to subsequent detection of manganese by FAAS. Under the optimized conditions, the method presented a detection limit of 0.7 μg L^− 1 and an enrichment factor of 17 to a volume of 3000 μL. The sampling frequency was 30 h^− 1. The accuracy of the method was tested by evaluating the amount of Mn in certified reference materials (apple leaves NIST 1515 and spinach leaves NIST 1570a). The proposed procedure was applied to food samples (shrimp powder, flaxseed flour, wheat flour, soy flour and oat), and the results agreed with those obtained by the determination of Mn in foods by atomic absorption spectrometry with electrothermal atomization (ETAAS).     

Evaluation of polychlorotrifluoroethylene as sorbent material for on-line solid phase extraction systems: determination of copper and lead by flame atomic absorption spectrometry in water samples

Polychlorotrifluoroethylene (PCTFE) in the form of beads was applied, as packing material for flow injection on-line column preconcentration and separation systems coupled with flame atomic absorption spectrometry (FAAS). Its performance characteristics were evaluated for trace copper determination in environmental samples. The on-line formed complex of metal with diethyldithiophosphate (DDPA) was sorbed on the PCTFE surface. Isobutyl methyl ketone (IBMK) at a flow rate of 2.8 mL min⁻¹ was used to elute the analyte complex directly into the nebulizer-burner system of spectrophotometer. The proposed sorbent material reveal, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates up to 15 mL min⁻¹ without loss of retention efficiency. For copper determination, with 90 s preconcentration time the sample frequency was 30 h⁻¹, the enhancement factor was 250, which could be further improved by increasing the loading (preconcentration) time. The detection limit (3s) was c_L = 0.07 μg L⁻¹, and the precision (R.S.D.) was 1.8%, at the 2.0 μg L⁻¹ Cu(II) level. For lead determination, the detection limit was c_L = 2.7 μg L⁻¹, and the precision (R.S.D.) 2.2%, at the 40.0 μg L⁻¹ Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials and by recovery measurements on spiked natural water samples.     

On-line preconcentration and determination of nickel in natural water samples by flow injection-inductively coupled plasma optical emission spectrometry (FI-ICP-OES)

An on-line nickel preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated to flow injection (FI) was studied. Trace amounts of nickel were preconcentrated by sorption on a conical minicolumn packed with activated carbon (AC) at pH 5.0. The nickel was removed from the minicolumn with 20% nitric acid. An enrichment factor of 80-fold for a sample volume of 50 ml was obtained. The detection limit (DL) value for the preconcentration method proposed was 82 ng l⁻¹. The precision for ten replicate determinations at the 0.5 μg l⁻¹ Ni level was 3.0% relative standard deviation (R.S.D.), calculated from the peak heights obtained. The calibration graph preconcentration method for nickel was linear with a correlation coefficient of 0.9997 at levels near the detection limits (DL) up to at least 100 μg l⁻¹. The method was successfully applied to the determination of nickel in natural water samples.     

Development of a flow system for the determination of low concentrations of silver using Moringa oleifera seeds as biosorbent and flame atomic absorption spectrometry

In this study a method for the determination of low concentrations of silver in waters using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry (FAAS) was developed. Moringa oleifera seeds were used as a biosorbent material. Chemical and flow variables of the on-line preconcentration system such as sample pH and flow rate, preconcentration time, eluent concentration and sorbent mass were studied. The optimum preconcentration conditions were obtained using sample pH in the range of 6.0-8.0, preconcentration time of 4 min at a flow rate of 3.5 mL min^− 1, 0.5 mol L^− 1 HNO₃ eluent at a flow rate of 4.5 mL min^− 1 and 35 mg of sorbent mass. With the optimized conditions, the preconcentration factor, precision, detection limit and sample throughput were estimated as 35 (for preconcentration of 14 mL sample), 3.8% (5.0 μg L^− 1, n = 7), 0.22 μg L^− 1 and 12 samples per hour, respectively. The developed method was successfully applied to mineral water and tap water, and accuracy was assessed through analysis of a certified reference material for water (APS-1071 NIST) and recovery tests, with recovery ranging from 94 to 101%.     

On-line liquid-liquid extraction system using a new phase separator for flame atomic absorption spectrometric determination of ultra-trace cadmium in natural waters

A robust flow injection (FI) on-line liquid-liquid extraction (LLE) preconcentration/separation system associated with a newly designed gravitational phase separator, coupled to flame atomic absorption spectrometry (FAAS) was developed. The performance of the system was illustrated for cadmium determination at the μg l⁻¹ level. The non-charged cadmium complex with ammonium pyrrolidine dithiocarbamate (APDC) was extracted on-line into isobutyl methyl ketone (IBMK). The organic phase was effectively separated from a large volume of aqueous phase and is led into a 100 μl loop of an injection valve before its introduction into the nebulizer. The system was optimized and offered good performance characteristics with unlimited life time of phase separator, greater flow rate ratios and improved flexibility, as compared with other solvent extraction preconcentration systems. With a sampling frequency of 33 h⁻¹, the enhancement factor was 155, the detection limit was 0.02 μg l⁻¹, the relative standard deviation was 3.2% at 2.0 μg l⁻¹ Cd concentration level and the calibration curve was linear over the concentration range 0.06-6.0 μg l⁻¹. The accuracy of the proposed method was evaluated by analyzing a certified reference material of water and by recovery measurements on spiked samples. Finally, it was successfully applied to the analysis of tapwater, river and seawater samples.     

Determination of trace elements in natural waters by inductively coupled plasma time of flight mass spectrometry after flow injection preconcentration in a knotted reactor

A flow injection on-line sorption system was developed for the separation and preconcentration of traces of Ag, Cd, Co, Ni, Pb, U and Y from natural water samples with subsequent detection by ICP TOF MS. Simultaneous preconcentration of the analytes was achieved by complexation with the chelating reagent 1-phenyl-3-methyl-4-benzoylpyrazol-5-one immobilized on the inner walls of a (200 cm × 0.5 mm) PTFE knotted reactor. The analytes were eluted and transported to an axial ICP TOF MS system with 1% (v/v) HNO₃ containing 0.3 μg l⁻¹ of Rh as an internal standard using ultrasonic nebulization. The detection limits (3σ) varied from 0.3 ng l⁻¹ for Y to 15.2 ng l⁻¹ for Ni and the precision (R.S.D.) was better than 4%. Using a loading time of 90 s and a sample flow rate of 4.5 ml min⁻¹, enhancement factors of 3-14 were obtained for the different analytes in comparison with their direct determination by ICP TOF MS with ultrasonic nebulization without preconcentration. The accuracy of the method was demonstrated by analysis of water based certified reference materials.     

Development of an on-line preconcentration system for zinc determination in biological samples

An on-line preconcentration system for zinc determination in 24-h urine, blood plasma and erythrocyte matrices by flame atomic absorption spectrometry (FAAS) was used. This procedure was based on adsorption of Zn(II) ions onto a minicolumn filled with silica gel, chemically modified with niobium(V) oxide (Nb₂O₅-SiO₂). The determination of the optimum conditions for Zn(II) preconcentration was done using two-level full factorial and Doehlert designs. In the optimization procedure, four variables (sample pH, eluent concentration, sample flow rate and eluent flow rate) were investigated. The results obtained from the full factorial design demonstrated that the sample pH and sample flow rate variables, and their interactions, were statistically significant. A Doehlert matrix was used in order to determine the optimum conditions for the sample pH and sample flow rate. The optimized conditions for sample pH and flow rate sampling were 6.6 and 7.1 ml min⁻¹, respectively, to obtain the maximum Zn(II) preconcentration and determination in the biological samples studied. Parameters of analytical curve, precision, effect of other ions in the proposed system and accuracy were achieved to assess the proposed method. The accuracy was confirmed by analysis of certified reference materials (urine Seronorm™ Trace Elements) and recovery tests in blood plasma and erythrocyte samples. Detection limit (3σ/S) of 0.77 μg l⁻¹, precision (calculated as relative standard deviation) of 1.5% for Zn(II) concentration of 10 μg l⁻¹ (n = 7) and a sampling frequency of 27 samples/h were obtained from the proposed system.     

Flow injection wetting-film extraction system for flame atomic absorption spectrometric determination of cadmium in environmental waters

A newly simple flow injection wetting-film extraction system coupled to flame atomic absorption spectrometry (FAAS) has been developed for trace amount of cadmium determination. The sample was mixed on-line with sodium diethyl dithiocarbamate and the produced non-charged Cd(II)-diethyl dithiocarbamate (DDTC) chelate complex was extracted on the thin film of diisobutyl ketone (DIBK) on the inner wall of the PTFE extraction coil. The wetting-film with the extracted analyte was then eluted by a segment of the cover solvent, and transported directly to the FAAS for evaluation. All the important chemical and flow parameters were optimized. Under the optimized conditions an enhancement factor of 35, a sample frequency of 22 h⁻¹ and a detection limit of c_L = 0.7 μg l⁻¹ Cd(II) were obtained for 60 s preconcentration time. The calibration curve was linear over the concentration range 1.5-45.0 μg l⁻¹ Cd(II) and the relative standard deviation, R.S.D. (n = 10) was 3.9%, at 10.0 μg l⁻¹ concentration level. The developed method was successfully applied to cadmium determination in a variety of environmental water samples as well as waste-water sample.     

The trace determination of some heavy metals in waters by flow-injection spectrophotometry and potentiometry

Three automated flow-injection systems are proposed for the determination of traces of manganese(II), lead and copper(II) in waters. The first system utilizes the catalytic effect of manganese(II) on the oxidation of N,N-diethylaniline by potassium periodate at pH 6.86–7.10 (30°C) and is used for spectrophotometric determination at 475 nm in the range 0.02–1.00 μg1^?1; the system involves reagent injection and stopped flow. The determination of lead in the range 0.7–100 μg1^?1 is based on spectrophotometric detection of the lead 4/(2-pyridylazo)resorcinol complex at 525 nm after on-line preconcentration of the sample (5–50 ml) on a minicolumn filled with Chelex-100 or Dowex 1-X8 resin. A potentiometric flow-injection system with a copper ion-selective electrode is applied for the determination of 0.5–1000 μg 1^?1 copper(II) after on-line preconcentration of 50–500 ml of sample on Chelex-100 resin. The procedures are tested on synthetic and real water samples, including sea water and waste-waters.     

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.