Kinetic spectrophotometric determination of Fe(II) in the presence of Fe(III) by H-point standard addition method in mixed micellar medium

The H-point standard addition method was applied to kinetic data for simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III). The method is based on the difference in the rate of complex formation between iron in two different oxidation states and methylthymol blue (MTB) at pH 3.5 in mixed cetyltrimethylammonium bromide (CTAB) and Triton X-100 micellar medium. Fe(II) can be determined in the range 0.25-2.5 microg ml(-1) with satisfactory accuracy and precision in the presence of excess Fe(III) and other metal ions that rapidly form complexes with MTB under working condition. The proposed method was successfully applied to the simultaneous determination of Fe(II) and Fe(III) or selective determination of Fe(II) in the presence of Fe(III) in spiked real environmental and synthetic samples with complex composition.     

Simultaneous kinetic determination of Fe(III) and Fe(II) by H-point standard addition method

The H-point standard addition method (HPSAM) was applied to kinetic data for simultaneous determination of Fe(III) and Fe(II) or selective determination of Fe(III) in the presence of Fe(II). The method is based on the difference in the rate of two processes; reduction of Fe(III) with Co(II) and subsequent complex formation of resulted Fe(II) with 1,10-phenanthroline, and direct complex formation between Fe(II) and 1,10-phenanthroline in pH 3 and cetyl trimethyl ammonium bromide, CTAB, micellar media. Fe(III) can be determined in the range of 0.75-5.13 mug ml(-1)with satisfactory accuracy and precision in the presence of excess Fe(II) under working conditions. The proposed method was successfully applied to the simultaneous determination of Fe(III) and Fe(II) and also to the selective determination of Fe(III) in the presence of Fe(II) in several synthetic mixtures containing different concentration ratios of Fe(III) to Fe(II).     

The use of 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine as a precolumn derivatizing reagent in HPLC determination for Fe(II) in natural samples.

3-(2-Pyridyl)-5,6-diphenyl-1,2,4-triazine (PDT) was used for the first time as a precolumn derivatizing reagent in the high-performance liquid chromatography (HPLC) method with UV absorbance detection for the Fe(II) determination. The Fe(II) reacts with PDT to form a magenta colored chelate in the presence of sodium dodecyl sulfate (SDS) and acetic acid-sodium acetate buffer solution medium of pH 4.65. The selection of maximum absorbance detection wavelength and the optimum composition of the organic modifier in the mobile phase were investigated in detail for the quantitative determination of Fe(II) using HPLC system. The formed Fe(II)-PDT chelate was satisfactorily separated from PDT on an Agilent Shim-pack ODS column (Eclipse XDB-C8, 4.6 x 150 mm) by isocratic elution with acetonitrile and 0.02 mol L(-1) acetic acid-sodium acetate buffer solution (pH 4.65, containing 0.02% of SDS and 60 x 10(-3) mol L(-1) NaClO(4)) as mobile phase at a flow rate of 1 mL min(-1), and monitored with a multiple wavelength detector. The detection limit (S/N = 3) is 0.35 ng mL(-1). Due to the excellent separation ability of HPLC, the innovative introduction of PDT as the precolumn derivatizing reagent, and the proper selection of the detect wavelength, the sensitivity of our newly developed HPLC method was enhanced remarkably compared to those of the common spectrophotometric methods. The developed HPLC method was successfully applied to the determination of Fe(II) in lake water samples.     

Octadecyl-bonded silica membrane disk modified with Cyanex302 for pre-concentration and determination of iron in food products

A simple and rapid method using an octadecyl-bonded silica membrane disk impregnated with Cyanex302 is described for the pre-concentration and determination of iron. The influence of various parameters on sorption and elution of Fe(III) were systematically investigated. The sorption of Fe(III) at pH 3.2 was quantitative (99.3 +/- 1.1%). It was completely recovered using 20 mL 5.0 M HCI and determined by flame atomic absorption spectrometry. Breakthrough volume of the modified disk for Fe(III) was >2000 mL, pre-concentration factor was >100, and reusability up to 28 cycles. The LOD and LOQ for Fe(III) were 0.45 microg/L and 1.51 microg/L, respectively, while precision for its determination in terms of RSD was < or =2.1%. This method was applied for Fe(III) determination in milk, fortified flour, cocoa powder, tea, and black pepper. To validate the procedure, EPA Method Standard (QC standard 21) was analyzed for Fe(III).     

Selective determination of trace iron in different oxidation states in natural water by flow injection-solid phase spectrometry

A novel method for the selective determination of Fe(II) and Fe(III) in water using 2-nitroso-5-[N-n-propyl-N-(3-sulfopropyl)amino]phenol (PSAP) was developed. QAE-Sephadex anion exchanger packed in a flow-through cell was used as a medium not only for both the concentration and the spectrophotometric measurements of the Fe-PSAP complex, but also for reduction of the Fe(III)-PSAP complex. The PSAP complex of Fe(II) or Fe(III) was strongly adsorbed on the anion exchanger in a weakly acidic to weakly basic region, but the Fe(III) complex was readily and completely reduced to the Fe(II) complex only in a neutral to weakly alkaline region in the solid phase. These properties were utilized to determine the Fe(II) and total Fe concentration without the addition of any reducing agent. The detection limits (3σ) were 0.18 ng for Fe(II) and 0.18 ng for total Fe using a 3.2-cm(3) sample solution. The present method is applicable to the determination of dissolved iron species present at μg dm(-3) levels in natural water samples.     

Spectrophotometric determination of Fe(II) with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine in the presence of large quantities of Fe(III) and complexing ions

A spectrophotometric method for the determination of Fe(II) in the presence of large amounts (up to 800 mg/l.) of Fe(III) is suggested. The Fe(III) is effectively masked by complexing with fluoride at pH 2.0-2.4 before development of the violet Fe(II) complex with 2,4,6-tri(2'-pyridyl)-1,3,5-triazine. The absorbance is measured at 595 nm. Various commonly occurring ions which complex with Fe(II) and/or Fe(III) do not interfere.     

Sensitive indirect spectrophotometric determination of isoniazid

A simple, rapid, sensitive and accurate indirect spectrophotometric method for the microdetermination of isoniazid (INH) in pure form and pharmaceutical formulations is developed. The procedure is based on the reaction of copper(II) with isoniazid in the presence of neocuproine (NC). In the presence of neocuproine, copper(II) is reduced easily by isoniazid to a Cu(I)-neocuproine complex, which shows an absorption maximum at 454 nm. By measuring the absorbance of the complex at this wavelength, isoniazid can be determined in the range 0.3-3.5 microgml-1. This method was applied to the determination of isoniazid in pharmaceutical formulation and enabled the determination of the isoniazid in microgram quantities (0.3-3.5 microgml-1). The results obtained for the assay of pharmaceutical preparations compared well with those obtained by the official method and demonstrated good accuracy and precision.     

Spectrophotometric determination of Fe(III) in alkaline solutions without neutralization

Spectrometric study on the complexation of Fe(III) with an organic reagent obtained by coupling 3-methyl-1-phenyl-5-pyrazolone with diazotized 3-hydroxy-4-amino-benzene sulphonic acid was carried out in alkaline solutions. A 1:2 Fe(III): reagent water soluble complex is formed. The optimum pH is 9.0-11.8. The maximum absorbance of the complex lies at lambda = 560 nm, where the absorbance of the reagent is low. The molar absorptivity is 9000 l.mole(-1).cm(-1) at pH = 11.6. The value of the stability constant determined at 20 +/- 1 degrees C, pH = 11.6 and lambda = 560 nm is 4 x 10(5)M. The Beer-Lambert law is followed for iron concentration in the 0.2-5.0 mug/ml range. The spectrophotometric method was tested on synthetic solutions and thus applied for determination of traces of Fe(III) in several samples of alkaline hydroxides and carbonates without the neutralization of the solutions.     

Collection of iron(III) from homogeneous aqueous solutions on membrane filters using Chromazurol B with Triton X-100.

A membrane filtration method was examined concerning the effective collection of iron(III) from a homogeneous aqueous solution with Chromazurol B (CAB), one of the triphenylmethane dyes, as a precipitating reagent in the presence of a non-ionic surfactant, polyethylene glycol mono[4-(1,1,3,3-tetramethylbutyl)phenyl]ether (Triton X-100). A formed blue Fe(III)-CAB complex was collected as a precipitate on a membrane filter by filtration under suction from a homogeneous aqueous solution in the pH range over about 2. The original solution was prepared at a concentration ratio of CAB to Fe(III) of to 10, and that of Triton X-100 to CAB of 10 to 100. It was then adjusted to a pH value of between 1.0 and 6.5. A linear relationship (r = 0.999) was obtained between the initial concentration and the found one of Fe(III) in the range of 2.0 x 10(-5) to 4.0 x 10(-4) mol dm(-3) at a fixed concentration ratio of CAB to Fe(III) of 3 and that of Triton X-100 to CAB of 20. This membrane filtration with CAB and Triton X-100 may be utilized for the separation of Fe(III) as a background species.     

Voltammetry of the iron(II)-{3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine} complex using GCE in acetonitrile

Summary During cyclic voltammetry the ferrous complex Fe(PDT) ₃ ²⁺ is both reduced and oxidized on a GCE in acetonitrile solvent. The reduction occurs in three steps, while during its oxidation, the Fe(III) species is generated at a more positive potential than the standard potential of the simple Fe(III)/Fe(II) couple. The anodic peak potential promises to be useful as a reference for measurements in non-aqueous solvents. The diffusion coefficient of the species in acetonitrile is reported.     

Spectrophotometric determination of some aromatic amines

A method for spectrophotometric determination of four aromatic amines is described. The method is based on the reaction between the amine and the colorless Fe(III)-ferrozine complex. The amine reduces iron from Fe(III) to Fe(II) which forms a violet colored complex with ferrozine. The method is suitable for to the determination of 1,4-phenylenediamine, 2,4-diaminotoluene, 8-aminoquinoline and 2-amino-3-hydroxypyridine. The effect of different factors such as; pH, stability of the complex, temperature, ferrozine concentration, Fe(III) concentration and methanol concentration have been studied. The composition of the complex as well as the tolerance amount of other amines have been reported. Maximum absorbance is at 562 nm and Beer's law is obeyed over the ranges 0.17-1.6 ppm for 1,4-phenylenediamine, 0.45-3.7 ppm for 2,4-diaminotoluene, 0.51-3.4 ppm for 8-aminoquinoline and 0.53-4.4 ppm for 2-amino-3-hydroxypyridine. The obtained molar absorbtivities were 4.7x10(4), 2.0x10(4), 1.6x10(4), 1.5x10(3) l mol(-1) cm(-1) respectively.     

Simultaneous kinetic determination of Fe(II) and Fe(III) based on their reactions with NQT4S in micellar media by using PLS and PCR methods

Simultaneous determination of Fe(II) and Fe(III) was studied using partial least squares regression (PLS) and principal component regression (PCR) methods. The models were based on the difference observed in the rates of the complex formation of iron in its two oxidation states with 1,2-naphthaquinone-2-thiosemicarbazone-4-sulphonic acid (NQT4S) at pH 4.0 in cetyltrimethylammoniumbromide (CTAB) as micellar media. The results showed that simultaneous determination of Fe(II) and Fe(III) could be performed in their concentration ranges of 0.10-2.10 and 0.25-2.25 μg/ml, respectively. The models used can proceed the data with low percent relative error of prediction (i.e. <5.5%). The procedure was successfully applied for the simultaneous determination of Fe(II) and Fe(III) in some environmental samples. The method would allow the transformation of the two oxidation states of iron to be monitored overtime in a water sample.     

A flow injection chemiluminescence system for the determination of isoniazid

A chemiluminescence (CL) flow system is described for the determination of isoniazid based on its enhancement on the chemiluminescence (CL) emission produced upon mixing a hexacyanoferrate(III) solution with an alkaline luminol solution. The system responds linearly to isoniazid concentration in the range 0-1 mg/L with a detection limit (3sigma) of 0.03 microg/L, relative standard deviation (RSD) of 1.2% for 0.1 mg/L isoniazid (n = 11). The system has been successfully applied to the determination of isoniazid in pharmaceutical preparations.     

Selective preconcentration, separation and speciation of ferric iron in different samples using N,N'-bis(2-hydroxy-5-bromo-benzyl)1,2 diaminopropane

The synthesis and analytical applications of N,N'-bis(2-hydroxy-5-bromo-benzyl)1,2 diaminopropane (HBDAP) are described. This compound reacts with Fe(III) in the range of pH 3-6 to produce a red complex (2:3 mol ratio of Fe(III)/HBDAP) soluble in chloroform. The investigation included a study of the characteristics that are essential for solvent extraction and for spectrophotometric determination and speciation of iron. A highly sensitive, selective and rapid spectrophotometric method is described for the determination of trace amounts of iron(III) by HBDAP. The complex obeys Beer's law from 0.056 to 1.68 mg l(-1) with an optimum range. The detection limit (taken as three times the standard deviation of the reagent blank) is approximately 1.23x10(-7) M Fe(III) and the limit of quantitation (taken as ten times the standard deviation of the reagent blank) is about 4.11x10(-7) M Fe(III). A single extraction gave a good separation of iron(III) from iron(II). Good separation of Fe(III) from Ni(II), Fe(II), Co(II), Cd(II), Mn(II), Zn(II), Pb(II) was also achieved at pH 3-5.     

Complexation equilibria and spectrophotometric determination of iron(III) with 1-amino-4-hydroxyanthraquinone

The complex equilibria of iron(III) with 1-amino-4-hydroxyanthraquinone (AMHA) were studied spectrophotometrically in 40% (v/v) ethanol and an ionic strength of 0.1M (NaClO(4)). The complexation reactions were demonstrated and characterized using graphical logarithmic analysis of the absorbance-pH graphs. A simple, rapid, selective and sensitive method for the spectrophotometric determination of trace amounts of Fe(III) is developed based on the formation of Fe(AMHA) complex at pH 2.5 (lambda(max) = 640 nm, epsilon approximately = 2.1 x 10(4) L. mol(-1) . cm(-1)) in the presence of a large number of foreign ions. Interferences caused by palladium(II) was masked by the addition of cyanide ions. The method has been applied to the determination of iron in some synthetic samples and polymetallic iron ores.     

Interfacial aggregate growth process of Fe(II) and Fe(III) complexes with pyridylazophenol in solvent extraction system

The complexation mechanism and aggregate formation of bis[2-(5-bromo-2-pyridylazo)-5-diethylaminophenolate] iron(II) and iron(III) complexes at the heptane-water interface were studied spectrophotometrically by the high-speed stirring method and the centrifugal liquid membrane method. Furthermore, the reduction process of the Fe(III) complex with ascorbic acid at the interface was spectrophotometrically observed. The chemical compositions of the interfacial aggregate of complexes have been proved by the X-ray photoelectron spectroscopy. The aggregation of the complex at the interface was observed as a red-shifted, very strong and narrower absorption band with respect to the absorption band of the monomer complex. The aggregate of Fe(III) complex showed more shifted spectrum than that of Fe(II) complex, which proposed the larger aggregation number of Fe(III) aggregate (n = 8) than that of Fe(II) aggregate (n = 3). The obtained rate constants of interfacial aggregation were smaller than rate constants of interfacial monomer complexation, because the formation of aggregate required the assembly of the monomers.     

Spectrophotometric determination of cobalt in iron-, cobalt- and nickel-base alloys

A spectrophotometric method has been developed for the accurate determination of cobalt at milligram level, based on oxidation of the cobalt(II)-EDTA complex with gold(III) chloride at pH 4.0-6.5 and 100 degrees and measurement of the absorbance of the resultant violet cobalt(III)-EDTA complex at 535 nm. The precision is not affected by the presence of several metal ions; including coloured ones such as Cu(II), Ni(II) and Fe(III). However, chromium(III) interferes since it also forms a violet complex with EDTA, but can be removed by separation with pyridine. Practical application of the method is illustrated by the determination of cobalt in alloys based on iron, cobalt and nickel. Over the cobalt range 8-52% the error ranges from 0.1 to 0.3%.     

Simple flow injection method for simultaneous spectrophotometric determination of Fe(II) and Fe(III)

The method is based on spectrophotometric determination of Fe(II) and Fe(III) at a single wavelength (530 nm) with the use of a dedicated reversed-flow injection system. In the system, EDTA solution is injected into a carrier stream (HNO₃) and then merged with a sample stream containing a mixture of sulfosalicylic acid and 1,10-phenanthroline as indicators. In an acid environment (pH ≅ 3) the indicators form complexes with both Fe(III) and Fe(II), but EDTA replaces sulfosalicylic acid, forming a more stable colourless complex with Fe(III), whereas Fe(II) remains in a complex with 1,10-phenenthroline. As a result, the area and minimum of the characteristic peak can be exploited as measures corresponding to the Fe(III) and Fe(II) concentrations, respectively. The analytes were not found to affect each other's signals, hence two analytical curves were constructed with the use of a set of standard solutions, each containing Fe(II) and Fe(III). Both analytes were determined in synthetic samples within the concentration ranges of 0.05–4.0 and 0.09–6.0 mg L⁻¹, respectively, with precision less than 1.5 and 2.6% (RSD) and with accuracy less than 4.3 and 5.6% (RE). The method was applied to determination of the analytes in water samples collected from artesian wells and the results of the determination were consistent with those obtained using the ICP-OES technique.     

A flow-through fluorescent sensor to determine Fe(III) and total inorganic iron

A flow-through fluorescent sensor for the consecutive determination of Fe(III) and total iron is described. The reactive phase of the proposed sensor, which has a high affinity for complexed Fe(III), consists of pyoverdin immobilized on controlled pore glass (CPG) by covalent bonding. This pigment selectively reacts with Fe(III) decreasing its fluorescence emission. Total inorganic iron is determined as Fe(III) after on-line oxidation in a mini-column containing persulphate immobilized on an ion exchange resin. The developed method allows the determination of Fe(III) in the 3-200 (g l(-1) range. The relative standard deviations of 10 determinations of 60 (g l(-1) of Fe(III) and 20 (g l(-1) of Fe(III)+Fe(II) are 3 and 5%, respectively. The sensor has been satisfactorily applied to speciate iron in synthetic, tap and well waters and wines. There were no significant differences for total inorganic iron determination between this new method and the atomic absorption spectroscopy reference method at the 95% confidence level. The sensor allows the concentration of Fe(II) to be calculated as the difference between total inorganic iron and Fe(III). The lifetime of the sensor is at least 3 months in continuous use or the equivalent of 1000 determinations.     

meso-四(4-磺酸基苯基)卟啉-铬黑T与铁(Ⅲ)混合显色反应的研究

本文研究了以铬黑T作TPPS_4和Fe(Ⅲ)的混合配位体,并在弱酸性条件下运用了铬黑T,首次突破了Fe(Ⅲ))与TPPS_4的成络反应条件:在pH4.0的HAc-NaAc缓冲溶液中,沸水浴加热15min,以1:1:1的组成形成TPPS_4-铬黑T-Fe(Ⅲ)混配络合物,λ_(max)=392um,ε＇=2.07×10~5L·mol~(-1)·cm~(-1),稳定常数为8.7×10~7,Fe(Ⅲ)含量在0～4.5μg/25ml范围内成线性关系.将此方法用于纯铜、茶叶、烟草样品中的痕量铁的测定,获得了较满意的结果.