Speciation of dissolved Fe(II) and Fe(III) in environmental water samples by micro-column packed with N-benzoyl-N-phenylhydroxylamine loaded on microcrystalline naphthalene and determination by electrothermal vaporization inductively coupled plasma-optical emission spectrometry

A novel solid phase extraction technique for the speciation of trace dissolved Fe(II) and Fe(III) in environmental water samples was developed by coupling micro-column packed with N-benzoyl-N-phenylhydroxylamine (BPHA) loaded on microcrystalline naphthalene to electrothermal vaporization inductively coupled plasma-optical emission spectrometry (ETV-ICP-OES). Various influencing factors on the separation and preconcentration of Fe(II) and Fe(III), such as the acidity of the aqueous solution, sample flow rate and volume, have been investigated systematically, and the optimized operation conditions were established. At pH 3.0 Fe(III) could be selectively retained by micro-column (20 mm × 1.4 mm, i.d.) packed with BPHA immobilized on microcrystalline naphthalene, and Fe(II) passed through the micro-column. Both Fe(II) and Fe(III) could be adsorbed by the micro-column at pH 6.5. Thus, the total Fe could be determined without the need for preoxidation of Fe(II) to Fe(III). The retained Fe(III) or the Fe(II) and Fe(III) was subsequently eluted by 0.1 ml of 1 mol l⁻¹ HCl. The adsorption capacity of the solid phase adsorption material was found to be 45.0 mg g⁻¹ for Fe(III) at pH 3.0 and 65.3 mg g⁻¹ for Fe(II) at pH 6.5, respectively. The detection limit (3σ) of 0.053 μg l⁻¹ was obtained with a practical enrichment factor of 156 at a sample volume of 17 ml. The relative standard deviations of 4.2% and 4.6% (C_Fe(III) = C_Fe(II) = 10 μg l⁻¹, n = 7) for Fe(III) and total iron were found, respectively. The method was successfully applied to the determination of trace Fe(II) and Fe(III) in environmental water samples (East Lake water, local tap water and mineral water). In order to validate the method, the developed method was applied to the determination of total iron in certified materials of NIES NO.10-b rice flour and GBW07605 tea leaves, and the results obtained were in good agreement with the certified values.     

Selective extraction, separation and speciation of iron in different samples using 4-acetyl-5-methyl-1-phenyl-1H-pyrazole-3-carboxylic acid

A method for speciation, preconcentration and separation of Fe(II) and Fe(III) in different matrices was developed using solvent extraction and flame atomic absorption spectrometry. 4-Acetyl-5-methyl-1-phenyl-1H-pyrazole-3-carboxylic acid (AMPC) was used as a new complexing reagent for Fe(III). The Fe(III)-AMPC complex was extracted into methyl isobutyl ketone (MIBK) phase in the pH range 1.0-2.5, and Fe(II) ion remained in aqueous phase at all pH. The chemical composition of the Fe(III)-AMPC complex was determined by the Job's method. The optimum conditions for quantitative recovery of Fe(III) were determined as pH 1.5, shaking time of 2 min, 1.64 × 10⁻⁴ mol L⁻¹ AMPC reagent and 10 mL of MIBK. Furthermore, the influences of diverse metal ions were investigated. The level of Fe(II) was calculated by difference of total iron and Fe(III) concentrations. The detection limit based on the 3σ criterion was found to be 0.24 μg L⁻¹ for Fe(III). The recoveries were higher than 95% and relative standard deviation was less than 2.1% (N = 8). The validation of the procedure was performed by the analysis of two certified standard reference materials. The presented method was applied to the determination of Fe(II) and Fe(III) in tap water, lake water, river water, sea water, fruit juice, cola, and molasses samples with satisfactory results.     

Novel catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine with 1,3-phenylenediamine and its applications to the determination of copper and iron at trace levels by flow injection technique

A new catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine (DPD) with 1,3-phenylenediamine (mPD) in the presence of hydrogen peroxide has been developed for trace metals analysis. The rate of the oxidation/coupling reaction can be enhanced significantly by iron, copper and cobalt. These metal ions can catalyze the oxidation reaction of DPD to form an oxidized product; the oxidized DPD was then coupled with mPD to give a blue-colored product which was measured spectrophotometrically at 650 nm. On the basis of such a reaction scheme, two simple flow injection analysis methods for the determination of copper and iron have been developed. Detailed studies on chemical and FIA variables affecting the sensitivity of the detection were carried out. Interferences from several ionic species were examined for the determination of copper: the interference effect by Fe(III) and Fe(II) up to 1.5 mg L⁻¹ was successfully suppressed by pretreating sample with ammonium acetate buffer solution (pH 8.4). Good linearity of a standard calibration graph was obtained over the ranges of 0-8 and 0-2 μg L⁻¹ of copper and iron, respectively, and the detection limits were 0.05 and 0.02 μg L⁻¹ for copper and iron, respectively. The precision of the methods in terms of relative standard deviation were 1.4 and 1.5% of R.S.D. which were obtained from 10 injections of 2.0 and 1.0 μg L⁻¹ of standard copper and iron, respectively. The proposed methods were successfully applied to the determination of copper and iron in tap and river water samples. The accuracy of the proposed methods was assessed by the analysis of certified reference material of river water.     

Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection

Sulfonylcalix[4]arenetetrasulfonate (SO₂CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO₂CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolith™ Performance RP-18e column and were eluted using a methanol (50 wt.%)-water eluent (pH 5.6) containing tetra-n-butylammonium bromide (7.0 mmol kg⁻¹), acetate buffer (5.0 mmol kg⁻¹), and disodium ethylendiamine-N,N,N′,N′-tetraacetate (0.10 mmol kg⁻¹). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [Al(III), Ba(II), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(II), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3σ blank basis were 8.8 nmol dm⁻³ (0.24 ng cm⁻³) for Al(III), 7.6 nmol dm⁻³ (0.42 ng cm⁻³) for Fe(III), and 17 nmol dm⁻³ (0.80 ng cm⁻³) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

Spectrophotometric catalytic determination of Fe(III) in estuarine waters using a flow-batch system

A flow-batch system was developed for the determination of Fe(III) in estuarine waters with high variability in salinity. The method is based on the catalytic effect of iron(III) on the oxidation rate of N,N-dimethyl-p-phenylenediammonium dichloride (DmPD) by hydrogen peroxide and the formed product is spectrophotometrically monitored at 554 nm. A controlled addition of sodium chloride to every assayed sample is accomplished for in-line individual salinity matching.The proposed system processes about 30 samples h⁻¹ and yields reproducible results. Relative standard deviations were estimated as <1.5% after 10 injections of typical samples (10.0-50.0 μg l⁻¹ Fe; ca. 0.5 mol l⁻¹ Cl). Synthetic samples (15.0 μg l⁻¹ Fe; 0.25-1.0 mol l⁻¹ NaCl) were efficiently processed, and no significant differences in results were found at a probability level of 99.7%. The method works for the full range of salinities. Only 120 μg DmPD are consumed per determination. The analytical curve is linear up to about 60 μg l⁻¹ Fe (r>0.999; n=5) and the detection limit is 5 μg l⁻¹ Fe. Results are in agreement with graphite furnace atomic absorption spectrometry.     

Solid-phase extraction of iron(III) with an ion-imprinted functionalized silica gel sorbent prepared by a surface imprinting technique

A new Fe(III)-imprinted amino-functionalized silica gel sorbent was prepared by a surface imprinting technique for selective solid-phase extraction (SPE) of Fe(III) prior to its determination by inductively coupled plasma atomic emission spectrometry (ICP-AES). Compared with non-imprinted polymer particles, the ion-imprinted polymers (IIPs) had higher selectivity and adsorption capacity for Fe(III). The maximum static adsorption capacity of the ion-imprinted and non-imprinted sorbent for Fe(III) was 25.21 and 5.10 mg g⁻¹, respectively. The largest selectivity coefficient of the Fe(III)-imprinted sorbent for Fe(III) in the presence of Cr(III) was over 450. The relatively selective factor (α_r) values of Fe(III)/Cr(III) were 49.9 and 42.4, which were greater than 1. The distribution ratio (D) values of Fe(III)-imprinted polymers for Fe(III) were greatly larger than that for Cr(III). The detection limit (3σ) was 0.34 μg L⁻¹. The relative standard deviation of the method was 1.50% for eight replicate determinations. The method was validated by analyzing two certified reference materials (GBW 08301 and GBW 08303), the results obtained is in good agreement with standard values. The developed method was also successfully applied to the determination of trace iron in plants and water samples with satisfactory results.     

Column system using diaion HP-2MG for determination of some metal ions by flame atomic absorption spectrometry

A column solid-phase extraction method for the preconcentration and determination of cadmium(II), copper(II), cobalt(II), iron(III), lead(II), nickel(II) and zinc(II) dithizone chelates by atomic absorption spectrometry has been described. Diaion HP-2MG was used as adsorbent for column studies. The influences of the various analytical parameters including pH of the aqueous solutions, amounts of ligand and resin were investigated for the retentions of the analyte ions. The recovery values are ranged from 95 to 102%. The influences of alkaline and earth alkaline ions were also discussed. The preconcentration factor was 375, when the sample volume and final volume are 750 and 2 ml, respectively. The detection limits of the analyte ions (k=3, N=21) were varying 0.08 μg/l for cadmium to 0.25 μg/l for lead. The relative standard deviations of the determinations at the concentration range of 1.8×10⁻⁴ to 4.5×10⁻⁵ mmol for the investigated elements were found to be lower than 9%. The proposed solid-phase extraction procedure were applied to the flame atomic absorption spectrometric determinations of analyte ions in natural waters (sea, tap, river), microwave digested samples (milk, red wine and rice) and two different reference standard materials (SRM1515 apple leaves and NRCC-SLRS-4 riverine water).     

Development of method for the speciation of inorganic iron in wine samples

In this paper, we proposed a procedure for the determination of iron(II) and total iron in wine samples employing molecular absorption spectrophotometry. The ligand used is 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and the chromogenic reaction in absence or presence of ascorbic acid (reducing agent) allows the determination of iron(II) or total iron, respectively. The optimization step was performed using a multivariate technique (Box Behnken design) involving the factors pH, acid ascorbic concentration and reaction time.The method allows the determination of iron(II) and iron(III) in wine samples, with limits of detection and quantification 0.22 and 0.72 μg L⁻¹, respectively. The precision expressed as relative standard deviation (R.S.D.) was 1.43 and 0.56% (both, n = 11) for content of iron(II) in wine samples of 1.68 and 4.65 mg L⁻¹, and 1.66 and 0.87% (both, n = 11) for content of total iron in wine samples of 1.72 and 5.48 mg L⁻¹.This method was applied for determination of iron(II) and total iron in six different wine samples. In these, the iron(II) content varied from 0.76 to 4.65 mg L⁻¹ and from 1.01 to 5.48 mg L⁻¹ for total iron. The results obtained in the determination of total iron by Br-PADAP method were compared with those that were performed after complete acid digestion in open system and determination of total iron employing FAAS. The method of regression linear was used for comparison of these results and demonstrated that there is no significant difference between the results obtained with these two procedures.     

Polymerization of acrylate monomers with MAO activated iron(II) and cobalt(II) complexes bearing tri- and tetradentate nitrogen ligands

Octahedral iron(II) and cobalt(II) based complexes, [N,N′-di(quinoline-2-methylene)-1,2-phenylenediimine]MCl₂, and [N,N′-di(quinoline-2-methylene)diiminocyclohexane]MCl₂ (M = Co and Fe), bearing tetradentate diimino nitrogen ligands were prepared and used in tert-butylacrylate (t-BA) polymerization after activation with methylaluminoxane (MAO). In general, polyacrylates with high molar mass and narrow molar mass distribution (MMD ≈ 2) were obtained. In order to understand the influence of the ligand on the polymerization process, polymerization behaviour of the hexacoordinated complexes was compared to pentacoordinated iron(II) and cobalt(II) complexes, 2,6-bis[1-(cyclohexylimido)ethyl]pyridine MCl₂ (M = Co and Fe), bearing tridentate diimine nitrogen ligands as well as to free iron(II) chloride. The ability of the MAO activated hexacoordinated complexes to polymerize methylacrylate (MA) and methyl methacrylate (MMA) was also considered, but reduced activities as well as lower molar mass polymers were obtained than in the experiments with t-BA.     

1-(2-Formamidoethyl)-3-phenylurea functionalized activated carbon for selective solid-phase extraction and preconcentration of metal ions

A novel method that utilizes 1-(2-formamidoethyl)-3-phenylurea-modified activated carbon (AC-1-(2-formamidoethyl)-3-phenylurea) as a solid-phase extractant has been developed for simultaneous preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) prior to the measurement by inductively coupled plasma atomic emission spectrometry (ICP-AES). Experimental conditions for effective adsorption of trace levels of Cr(III), Cu(II), Fe(III) and Pb(II) were optimized using batch and column procedures in detail. The optimum pH value for the separation of metal ions simultaneously on the new sorbent was 4. And the adsorbed metal ions could be completely eluted by using 2.0 mL 2.0 mol L⁻¹ HCl solution. Common coexisting ions did not interfere with the separation and determination of target metal ions. The maximum static adsorption capacity of the sorbent at optimum conditions was found to be 39.8, 39.9, 77.8 and 17.3 mg g⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The detection limits of the method were found to be 0.15, 0.41, 0.27 and 0.36 ng mL⁻¹ for Cr(III), Cu(II), Fe(III) and Pb(II), respectively. The relative standard deviation (RSD) of the method was lower than 4.0% (n = 8). The method was successfully applied for the preconcentration of trace Cr(III), Cu(II), Fe(III) and Pb(II) in natural and certified samples with satisfactory results.     

The use of anion-exchange disks in an optrode coupled to a multi-syringe flow-injection system for the determination and speciation analysis of iron in natural water samples

A combination of multi-syringe flow-injection analysis (MSFIA) technique with an optical fibre reflectance sensor for the determination of iron in water samples has been developed in this work. Anion-exchange solid phase extraction (SPE) disks have been used as solid phase. Ammonium thiocyanate has been chosen as chromogenic reagent for Fe(III). The complex Fe[SCN]₆³⁻ is retained onto the SPE disk and spectrophotometrically detected at 480 nm. The complex is eluted with 0.25 mol l⁻¹ hydrochloric acid in 75% ethanol. Total iron can be determined by oxidising Fe(II) to Fe(III) with hydrogen peroxide.A mass calibration was run within the range of 0.4-37.5 ng. The detection limit (3s_b/S) was 0.4 ng. The repeatability (RSD), calculated from 9 replicates using 0.5 ml injections of a 25 μg l⁻¹ concentration, was 3.6%. The repeatability between five anion-exchange disks was 5.4%. An injection throughput of 7 injections per hour for a sampling volume of 1 ml has been achieved.The applicability of the proposed methodology in natural water samples has been proved.The properties of anion-exchange and chelating SPE disks have been studied and compared.     

Biosorption of copper(II), lead(II), iron(III) and cobalt(II) on Bacillus sphaericus-loaded Diaion SP-850 resin

The biosorption of copper(II), lead(II), iron(III) and cobalt(II) on Bacillus sphaericus-loaded Diaion SP-850 resin for preconcentration-separation of them have been investigated. The sorbed analytes on biosorbent were eluted by using 1 mol L⁻¹ HCl and analytes were determined by flame atomic absorption spectrometry. The influences of analytical parameters including amounts of pH, B. sphaericus, sample volume etc. on the quantitative recoveries of analytes were investigated. The effects of alkaline, earth alkaline ions and some metal ions on the retentions of the analytes on the biosorbent were also examined. Separation and preconcentration of Cu, Pb, Fe and Co ions from real samples was achieved quantitatively. The detection limits by 3 sigma for analyte ions were in the range of 0.20-0.75 μg L⁻¹ for aqueous samples and in the range of 2.5-9.4 ng g⁻¹ for solid samples. The validation of the procedure was performed by the analysis of the certified standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 2711 Montana soil and GBW 07605 Tea). The presented method was applied to the determination of analyte ions in green tea, black tea, cultivated mushroom, boiled wheat, rice and soil samples with successfully results.     

Alumina modified by dimethyl sulfoxide as a new selective solid phase extractor for separation and preconcentration of inorganic mercury(II)

Dimethyl sulfoxide (DMSO) was simply immobilized to neutral alumina via quite strong hydrogen bonding between sulfoxide oxygen and surface alumina hydroxo groups. The produced alumina-modified dimethyl sulfoxide (AMDMSO) solid phase (SP)-extractor experienced high thermal and medium stability. Moreover, the small and compact size of DMSO moiety permit high surface coverage evaluated to be 2.1 ± 0.1 mmol g⁻¹ of alumina. Hg(II) uptake was 1.90 mmol g⁻¹(distribution coefficient log K_d = 5.658) at pH 1.0 or 2.0, 1.68 mmol g⁻¹ (log K_d = 4.067) at pH 3.0 or 4.0 while the metal ions Ca(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) showed low values 0.513-0.118 mmol g⁻¹ (log K_d < 3.0) in the pH range 4.0-7.0. A mechanism was suggested to explain the unique uptake of Hg(II) ions by binding as neutral and chloroanionic species predominate at pH values ≤ 3.0 of a medium rich in chloride ions. A direct and fast batch separation mode was achieved successfully to retain selectively Hg(II) in presence of other eight coexisting metal ions. Thus, Hg(II) was completely retained; Ca(II), Co(II), Ni(II) and Cd(II) were not retained, while Pb(II), Cu(II), Zn(II) and Fe(III) exhibited very low percentage retention evaluated to be 0.42, 0.49, 1.4 and 5.43%, respectively. The utility of the new modified alumina sorbent for concentrating of ultratrace amounts of Hg(II) was performed by percolating 2 l of doubly distilled water, drinking tap water, and Nile river water spiked with 10 ng/l over 100 mg of the sorbent packed in a minicolumn used as a thin layer enrichment bed prior to the determination by CV-AAS. The high recovery values obtained (98.5 ± 0.5, 98.5 ± 0.5 and 103.0 ± 1.0) based on excellent enrichment factor 1000, along with a good precision (R.S.D.% 0.51-0.97%, N = 3) demonstrate the accuracy and validity of the new modified alumina sorbent for preconcentrating ultratrace amounts of Hg(II) with no matrix interference.     

Luminescent hexanuclear Cu(I)-cluster for the selective determination of copper

For the first time, the formation of a luminescent hexanuclear cluster has been used for the selective determination of copper. In aqueous solutions, the non-luminescent ligand N-ethyl-N′-methylsulfonylthiourea (EMT) forms an intensely red luminescent hexanuclear Cu(I)-cluster with an emission maximum at 663 nm only with Cu(II) ions. The intensity of the luminescence is proportional to the Cu(II) concentration and allows for selective Cu determinations in the μg l⁻¹-range. Ubiquitous metal ions such as Fe(III), Al(III), Ca(II), Mg(II), and alkaline metal ions, as well as other heavy metal ions, e.g. Co(II), Ni(II), Zn(II), Cd(II), Hg(II), and Pb(II) are tolerated in concentrations up to 50 mg l⁻¹. The detection limit for Cu(II) in aqueous solution, calculated according to Funk et al. [Qualitätssicherung in der Analytischen Chemie, Verlag Chemie, Weinheim, 1992], is 113 μg l⁻¹. The cluster formation has been used for the quantitative analysis of copper in tap water and in industrial water, as well as for the localization of copper adsorbed by activated-sludge flocs.     

Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L⁻¹ for Sb(III) and 9.2 ng L⁻¹ for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL⁻¹, n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.     

Solid phase extraction-spectrophotometric determination of fluoride in water samples using magnetic iron oxide nanoparticles

A new, sensitive, fast and simple method using magnetic iron oxide nanoparticles (MIONs), as an adsorbent has been developed for extraction, preconcentration and determination of traces of fluoride ions. The determination method is based on the discoloration of Fe(III)-SCN complex with extracted fluoride ions which was subsequently monitored spectrophotometrically at λ_max = 458 nm. Various parameters affecting the adsorption of fluoride by the MIONs have been investigated, such as pH of the solution, type, volume and concentration of desorbing reagent, amount of adsorbent and interference effects. A linear response for the determination of fluoride was achieved in the concentration range of 0.040-1.250 μg mL⁻¹. The limit of detection (LOD) and limit of quantification (LOQ) for fluoride based on 3 times and 10 times the standard deviation of the blank (3S_b, 10S_b) were 0.015 and 0.042 μg mL⁻¹ (n = 20) for fluoride ion, respectively. A preconcentration factor of 50 was achieved in this method. The proposed procedure has been applied for determination of fluoride concentration in various water samples. The results obtained from this method were successfully compared with those provided by standard SPADNS method.     

A simple and green analytical method for determination of iron based on micro flow analysis

A simple, inexpensive and reagent-less colorimetric micro flow analysis (μFA) system was implemented in a polymethyl methacrylate (PMMA) micro fluidic manifold. A T-shaped micro channel on a PMMA chip was fabricated by laser ablation and topped with molded polydimethylsiloxane (PDMS). The fabricated μFA system was integrated with the optical components as detector and applied to the determination of iron in water samples. It is based on the measurement of Fe(III)-nitroso-R salt complex at 720 nm formed by the reaction between Fe(III) and nitroso-R salt in an acetate buffer solution pH 5. The proposed μFA consumed very small amount of reagent and sample, it released waste of less than 2.0 mL h⁻¹. The relative standard deviation (R.S.D.) was less than 2% (n = 11) with the recovery of 98.7 ± 0.12 (n = 5). The linear range for the determination of iron in water samples was over the range of 0.05-4.0 μg mL⁻¹ with a correlation coefficient (r²) of 0.9994. The limit of detection (3σ) and limit of quantitation (10σ) were 0.021 μg mL⁻¹ and 0.081 μg mL⁻¹, respectively with a sample throughput of 40 h⁻¹.     

New method for simultaneous determination of Fe(II) and Fe(III) in water using flow injection technique

The method exploits the possibilities of flow injection gradient titration in a system of reversed flow with spectrophotometric detection. In the developed approach a small amount of titrant (EDTA) is injected into a stream of sample containing a mixture of indicators (sulfosalicylic acid and 1,10-phenanthroline). In acid environment sulfosalicylic acid forms a complex with Fe(III), whereas 1,10-phenanthroline forms a complex with Fe(II). Measurements are performed at wavelength λ = 530 nm when radiation is absorbed by both complexes. After injection EDTA replaces sulfosalicylic acid and forms with Fe(III) more stable colourless complex. As a result, a characteristic “cut off” peak is registered with a width corresponding to the Fe(III) concentration and with a height corresponding to the Fe(II) concentration. Calibration was performed by titration of four two-component standard solutions of the Fe(II)/Fe(III) concentrations established in accordance with 2² factorial plan. The method was tested with the use of synthetic samples and then it was applied to the analysis of water samples taken from artesian wells. Under optimized experimental conditions Fe(II) and Fe(III) were determined with precision less than 0.8 and 2.5% (RSD) and accuracy less than 3.2 and 5.1% (relative error) within the concentration ranges of 0.1-3.0 and 0.9-3.5 mg L⁻¹ of both analytes, respectively.     

A novel detection approach based on chromophore-decolorizing with free radical and application to photometric determination of copper with acid chrome dark blue

A novel detection approach named chromophore-decolorizing with free radicals is developed for determination of trace heavy metal. The hydroxyl radicals (HO) generated from Fe(III) and hydrogen peroxide will oxidize the free chromophore into almost colorless products. The copper-acid chrome dark blue (ACDB) complexation was investigated at pH 5.07. In the presence of Fe(III) and hydrogen peroxide, the excess ACDB was decolorized in the Cu-ACDB reaction solution, and the final solution contained only one color compound, the Cu-ACDB complex. After oxidation of free hydroxyl radicals, the complexation becomes sensitive and selective and it has been used for the quantitation of trace amounts of Cu(II) dissolved in natural water. Beer's law is obeyed in the range from 0 to 0.500 μg mL⁻¹ Cu(II) and the limit of detection is only 6 μg L⁻¹ Cu(II). Besides, the Cu-ACDB complex formed was characterized.