Application of artificial neural networks in multifactor optimization of an FIA system for the determination of aluminium

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results.     

Application of artificial neural networks in multifactor optimization of an FIA system for the determination of aluminium

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results. Received: 26 May 1999 / Revised: 29 July 1999 / Accepted: 17 August 1999     

Simultaneous determination of Ru(III) and Rh(III) using octadecyldithiocarbamate by first-derivative spectrophotometry

A first-derivative spectrophotometric method is described for the simultaneous determination of Ru(III) and Rh(III) using octadecyl dithiocarbamate. The complexes are insoluble in water, but easily extractable into chloroform. Quantitative determination of Ru(III) and Rh(III) is possible in the ranges 0.5-6.0 mug ml(-1) and 1.0-10.0 mug ml(-1) respectively, with a standard deviation of +/-0.10. A statistical evaluation of the experimental results is reported.     

Preconcentration of trace copper with yeast for river water analysis

A sensitive and selective method has been introduced for the determination of ultra trace amounts of Ru(III) based on its catalytic effects on the oxidation of Brilliant green (BG) by sodium bromate. A flow injection method has been used with spectrophotometric detection. The method is based on measuring the decrease in absorbance of BG at lambda(max)=615 nm. The decrease in absorbance of BG is linear with the concentration range of 0.005-0.500 mug ml(-1) Ru(III). The limit of detection is 0.002 mug ml(-1). The influence of reagent concentration, manifold parameter and potential interference species has been investigated. The method was used for the determination of ruthenium in synthetic samples with satisfactory results.     

Kinetic-spectrophotometric determination of trace amounts of As(III) based on its inhibitory effect on the redox reaction between bromate and hydrochloric acid

A simple, sensitive, rapid and reliable method has been developed for spectrophotometric determinations of As(III) in the presence of As(V) based on its inhibition effect on the redox reaction between bromate and hydrochloric acid. The decolorization of methyl orange by the reaction products was used to monitor the reaction spectrophotometrically at 525 nm. The method allows the determination of arsenic in the range of 6-1000 mug l(-1). The relative standard deviation for 10 determinations of 40 mug l(-1) of As(III) was 1.43% and the limit of detection, corresponding to a signal to noise ratio of three, was 3.4 mug l(-1). The proposed method was applied to the determination of As(III) in water samples with satisfactory results.     

Chromium speciation by a surfactant-coated alumina microcolumn using electrothermal atomic absorption spectrometry

A simple and convenient method has been developed for the speciation of chromium(III) and chromium(VI) in aqueous solutions using a sodium dodecyl sulphate coated alumina micro-column (1.5 cm x 5 mm i.d.) and graphite furnace-atomic absorption spectrometry (GF-AAS). Under the optimized conditions (pH 0.6, adjusted with hydrochloric acid; flow rate, 1 ml min(-1)) chromium(VI) is retained on the column and chromium(III) is collected and determined by GF-AAS. Total chromium is directly determined by GF-AAS and chromium(VI) is calculated by difference. The relative standard deviations (10 replicate analyses) at the 20 mug l(-1) level for chromium(III) and chromium(VI) and at the 40 mug l(-1) level for total chromium were 1.4%, 3.6% and 1.8%, and the corresponding limits of detection (based on 3sigma) were 0.57 mug ml(-1), 0.61 mug ml(-1) and 0.35 mug l(-1) respectively. No large interference effects have been observed from other investigated species and the method has been successfully applied to a range of water samples.     

Simultaneous first-derivative spectrophotometric determination of iron(III) and molybdenum(VI) in cobalt-chromium and nickel-chromium alloys

A method is proposed for the simultaneous determination of iron(III) and molybdenum(VI) by first-derivative spectrophotometry based on the absorption spectra of their complexes with morin in the presence of a cationic surfactant. The zero-crossing measurement technique is found sutiable for the direct measurement of the first-derivative value at the specified wavelengths. Iron(III) (0.9-1.5 mug ml(-1)) and molybdenum(VI) (0.3-4.2 mug ml(-1)) in different ratios have been determined simultaneously. A critical evaluation of the proposed method is performed by statistical analysis of the experimental data. The method was applied to determine iron and molybdenum in different alloys.     

Determination of antimony(III) in environmental water samples in microemulsion system by the fluorescence quenching method

A novel highly sensitive and selective fluorescent reagent, 2,6,7-trihydroxy-9-(3,5-dibromo-4-hydroxyphenyl)fluorone (DBH-PF) has been studied for the spectrofluorimetic determination of antimony(III) in cetyltrimethylammonium bromide (CTMAB) microemulsion media. DBH-PF reacts with antimony(III) forming a complex with 1:2 (metal to ligand) antimony-DBH-PF in the system of HAc-NaAc buffer solution at pH 5.33. The maximum excitation and emission wavelengths are at 522 and 556 nm, respectively. The linear range of the method is 0.05 approximately 1.50 mug 10 ml(-1) and the detection limit is 0.015 mug 10 ml(-1). Foreign ions are eliminated by preconcentration and separation with sulfhydryl dextrose gel (SDG) at pH 1.0. The proposed method has been applied to the determination of antimony(III) in industrial waste water samples with satisfactory results.     

Colour reaction of chromium (VI) with N,N-diethyl-1,4-phenylenediame in the presence of ethanol and cyclohexyldiamine tetraacetic acid as well as its application in the species analysis of chromium

A simple, rapid and precise spectrophotometric method for the determination of Chromium (III and IV) has been developed. The reaction of Cr(VI) with N,N-diethyl-1,4-phenylenediamine is almost complete in a twinkling, which yields a red product with a wavelength of maximum absorption at 530 nm. Beer's Law is obeyed in the Cr concentration range of 0-2.0 mug ml(-1). The molar absorptivity is 5.0x10(4) l mol(-1) cm(-1), limit of detection 0.002 mug ml(-1) and relative SD=1.13% for 5.04 mug Cr. The colouring rate and absorbance are not noticeably affected by temperature from 2 to 45 degrees C. The amounts of Cr(VI) and Cr(III) were measured by determining Cr(VI) first under the condition of masking Cr(III) by cyclohexyldiamine tetraacetic acid, and then the total amount by oxidation of Cr(III). The method was applied to the analyses of some industrial waste waters containing Cr with satisfactory results.     

Separation of antimony(III) with iodide and dithizone by sorption on polyurethane foam from sulphuric acid medium for its spectrophotometric determination in glasses

A method for quantitative separation of antimony(III) by sorption on polyether based polyurethane foam and its spectrophotometric determination has been described. The method involves formation of a pink-red complex of antimony(III) with iodide (0.045M) and dithizone (2.3 x 10(-5)M) in 0.25-0.75M H(2)SO(4) medium, sorption of the complex on polyurethane foam (within 45 min) at room temperature followed by its elution with acidified acetone (acetone containing 0.008% H(2)SO(4)) and spectrophotometric measurement at 507.2 nm ( = 2.56 x 10(4) l mol cm). The method obeys Beer's law from 0.1 to 6.0 mug antimony(III). Tolerance limits of other ions are Co (100 mug), Ni (100 mug), Fe (10 mug), Cu (0.5 mug), Sn (20 mug), Zn (100 mug), As (100 mug), Mn (200 mug), Pb (50 mug), Ti (100 mug), V (50 mug), etc. Interference by iron and copper have been eliminated by treating with KOH prior to the extraction of antimony. The method has been standardized with glass samples spiked with known amounts of antimony and applied to the determination of antimony in various glasses.     

The study and application of biomimic peroxidase ferric 2-hydroxy-1-naphthaldehyde thiosemicarbazone (Fe(III)-HNT)

Ferric 2-hydroxy-1-naphthaldehyde thiosemicarbazone (Fe(III)-HNT) has been synthesized and used to mimic the active group of horseradish peroxidase (HRP). The catalytic characteristics of this mimic-enzyme catalyst in the oxidation reaction of ascorbic acid with hydrogen peroxide has been studied. The experimental results showed that this peroxidase model compound has similar catalytic activity that of HRP. The catalytic activity of Fe(III)-HNT has been compared with those of HRP and common mimic-enzymes, metalloporphyrins (e.g. metal tetrakis(sulphophenyl)porphyrin (Me-TPPS(4))). Though the catalytic activity of Fe(III)-HNT is 75% of that of HRP, it can be used as a new kind of mimic-enzyme catalyst in determination of trace H(2)O(2). By coupling this mimetic catalytic reaction with the catalytic reaction of glucose oxidase, glucose can be determined indirectly. Under experimental conditions the linear relationship between DeltaA(265) and glucose concentration was in the range of 2.0-40.0 mug ml(-1), The correlation coefficient (r) was 0.9996. The R.S.D. (P=0.05, n=6) was 0.24%. The detection limit was determined to be 0.238 mug ml(-1). It was applied successfully to the determination of glucose in normal human and diabetic urine. The values of determination by the proposed method were compared with those of a routine method (enzymic glucose determination) applied in an hospital clinical laboratory. The agreement was very good.     

Spectrophotometric determination of bismuth(III) with o-hydroxyhydroquinonephthalein in the presence of Brij 58

A simple and sensitive spectrophotometric determination of bismuth(III) is based on the reaction between bismuth(III) and o-hydroxyhydroquinonephthalein in the presence of Brij 58 in acidic media. The calibration graph is linear over the range 0-3.5 mug/ml bismuth(III) in the final solution, and the apparent molar absorptivity at 520 nm is 9.03 x 10(4) l. mole(-1). cm(-1). The proposed method is 2-10 times more sensitive than other methods, and simpler. It has been applied to the assay of bismuth(III) in pharmaceutical preparations, such as dermatol and bismuth subnitrate, with good results.     

Ferromagnetic interactions in Ru(III)-nitronyl nitroxide radical complex: a potential 2p4d building block for molecular magnets

The reaction between [Ru(salen)(PPh3)Cl] and the 4-pyridyl-substituted nitronyl nitroxide radical (NITpPy) leads to the [Ru(salen)(PPh3)(NITpPy)](ClO4)(H2O)2 complex while the reaction with the azido anion (N3-) leads to the [Ru(salen)(PPh3)(N3)] complex 2 (where salen2- = N,N'-ethan-1,2-diylbis(salicylidenamine) and PPh3 = triphenylphosphine). Both compounds have been characterized by single crystal X-ray diffraction. The two crystal structures are composed by a [Ru(III)(salen)(PPh3)]+ unit where the Ru(III) ion is coordinated to a salen2- ligand and one PPh3 ligand in axial position. In 1 the Ru(III) ion is coordinated to the 4-pyridyl-substituted nitronyl nitroxide radical whereas in 2 the second axial position is occupied by the azido ligand. In both complexes the Ru(III) ions are in the same environment RuO2N3P, in a tetragonally elongated octhaedral geometry. The crystal packing of 1 reveals pi-stacking in pairs. While antiferromagnetic intermolecular interaction (J2 = 5.0 cm(-1)) dominates at low temperatures, ferromagnetic intramolecular interaction (J1 = -9.0 cm(-1)) have been found between the Ru(III) ion and the coordinated NITpPy.     

Spectrophotometric determination of bismuth with semi-xylenol orange and its application in metal analysis

Semi-Xylenol Orange forms a 2 : 1 chelate with bismuth(III), which has a logarithmic value of 3.08 for its conditional formation constant and a molar absorptivity of 4.2 x 10(4) l.mole(-1).cm(-1). Beer's law is obeyed at 540 nm over the range 10-30 mug of Bi(III), with a standard deviation of 1.1 mug (n = 18). Lactic acid is used as an auxiliary complexing agent to prevent olation and oxolation. Interference from up to 1.3 mg of copper can be eliminated by the combined use of masking Cu(II) with thiourea, ascorbic acid and thiosemicarbazide and "post-masking" Bi(III) with sodium chloride. The proposed method has been successfully applied to the direct determination of 0.002% of Bi in lead metal, with a coefficient of variation varying from 3.7 to 6.9%.     

Flow-injection chemiluminescence determination of quinine using on-line electrogenerated cobalt(III) as oxidant

A novel chemiluminescence (CL) flow system for the determination of quinine is described. It is based on the direct chemiluminescence reaction of quinine and cobalt(III) in sulfuric acid medium. The unstable Co(III) was on-line electrogenerated by constant-current electrolysis. The chemiluminescence intensity was linear with a quinine concentration in the range of 0.1-100 mug ml(-1). The determination limit was 3.3x10(-8) g ml(-1). The whole process could be completed in 1 min. The proposed method is suitable for automatic and continuous analysis, and has been applied successfully to the analysis of quinine in pharmaceutical preparation.     

Chemiluminescence determination of some fluoroquinolone derivatives in pharmaceutical formulations and biological fluids using [Ru(bipy)(3)(2+)]-Ce(IV) system

A new chemiluminescence (CL) method using flow injection has been described for the rapid and sensitive determination of three fluoroquinolone derivatives, namely ofloxacin, norfloxacin and ciprofloxacin hydrochloride. The method is based on the CL reaction of the studied fluoroquinolones with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bipy)(3)(2+)] and Ce(IV) in sulfuric acid medium. Under the optimum conditions, the CL intensity is proportional to the concentration of the drugs in solution over the range 0.05-7.0 mug ml(-1) for norfloxacin, 0.05-6.0 mug ml(-1) for ciprofloxacin hydrochloride and 0.003-0.7 mug ml(-1) for ofloxacin. The limits of detection (s/n=3) were 3.1x10(-8) M norfloxacin, 2.6x10(-8) M ciprofloxacin hydrochloride and 5.5x10(-9) M ofloxacin. The method was applied successfully to the determination of these compounds in dosage forms and biological fluids.     

Application of Artificial Neural Networks in Multifactor Optimization of Selectivity in Capillary Electrophoresis

ABSTRACT

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) was proposed in the optimization of selectivity in capillary electrophoresis. The effect of the buffer composition, concentration, SDS concentration, ethanol percentage and the applied voltage on the separation of six choice solutes was examined by using orthogonal design. Feedforward-type neural networks with faster back propagation (BP) algorithm were applied to model the separation process, and then optimization of the experimental conditions was carried out in the modeled neural network with 5-7-1 structure, which had been confirmed to be able to provide the maximum performance. It was demonstrated that by combining ANN modeling with experimental design, the number of experiments necessary to search and find optimal separation conditions can be reduced significantly. Because of its general validity, the new proposed approach can also be applied in other separation conditions.     

A new coordination mode of the photometric reagent glyoxalbis(2-hydroxyanil) (H2gbha): bis-bidentate bridging by gbha2- in the redox series [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2), including a radical-bridged diruthenium(III) and a Ru(III)/Ru(IV) intermediate

The bis-bidentate bridging function of gbha2- with N,O-/N,O- coordination was observed for the first time in the complex (mu-gbha)[Ru(III)(acac)2]2 (1). Density functional theory calculations of 1 yield a triplet ground state with a large (deltaE > 6000 cm(-1)) singlet-triplet gap. Intermolecular antiferromagnetic coupling was observed (J approximately -5.3 cm(-1)) for the solid. Complex 1 undergoes two one-electron reduction and two one-electron oxidation steps; the five redox forms [(mu-gbha)[Ru(acac)2]2]n (n = -2, -1, 0, +1, +2) were characterized by UV-vis-NIR spectroelectrochemistry (NIR = near infrared). The paramagnetic intermediates were also investigated by electron paramagnetic resonance (EPR) spectroscopy. The monoanion with a comproportionation constant K(c) of 2.7 x 10(8) does not exhibit an NIR band for a Ru(III)/Ru(II) mixed-valent situation; it is best described as a 1,4-diazabutadiene radical anion containing ligand gbha*3-, which binds two ruthenium(III) centers. A Ru(III)-type EPR spectrum with g1 = 2.27, g2 = 2.21, and g3 = 1.73 is observed as a result of antiferromagnetic coupling between one Ru(III) and the ligand radical. The EPR-active monocation (K(c) = 1.7 x 10(6)) exhibits a broad (deltanu(1/2) = 2600 cm(-1)) intervalence charge-transfer band at 1800 nm, indicating a valence-averaged (Ru3.5)2 formulation (class III) with a tendency toward class II (borderline situation).     

Structure and photochemical properties of (mu-alkoxo)bis(mu-carboxylato)diruthenium complexes with naphthylacetate ligands

Two new dinuclear Ru(III) complexes containing naphthalene moieties, K[Ru2(dhpta)(mu-O2CCH2-1-naph)2] (1) and K[Ru2(dhpta)(mu-O2CCH2-2-naph)2] (2) (H5dhpta = 1,3-diamino-2-hydroxypropane-N,N,N',N'-tetraacetic acid, naph-1-CH2CO2H = 1-naphthylacetic acid, naph-2-CH2CO2H = 2-naphthylacetic acid), were synthesized. Complex 2 crystallized as an orthorhombic system having a space group of Pbca with unit cell parameters a = 10.6200(5) A, b = 20.270(1) A, c = 35.530(2) A, and Z = 8. EXAFS analysis of 1 and 2 in the solid states and in solution clarified that the dinuclear structures of 1 and 2 were kept in DMSO solutions. Variable-temperature magnetic susceptibility data indicated that the two Ru(III) centers are strongly antiferromagnetically coupled as shown by the large coupling constants, J = -581 cm(-1) (1) and -378 cm(-1) (2). In the cyclic voltammograms of 1 and 2, one oxidation peak and two reduction peaks which were assigned to the redox reaction of the ruthenium moieties were observed in DMF. The large conproportionation constants estimated from the reduction potentials of Ru(III)Ru(III) and Ru(III)Ru(II) indicated the great stability of the mixed-valent state. The mixed-valent species [Ru(III)Ru(II)(dhpta)(mu-O2CCH2-R)2](2-) (R = 1-naph (6) and R = 2-naph (7)) were prepared by controlled potential electrolysis of 1 and 2 in DMF. The electronic absorption spectra of 6 and 7 were similar to that of [Ru(III)Ru(II) (dhpta)(mu-O2CCH3)2](2-) which is a typical Class II type mixed-valent complex. The fluorescence decay of 1 and 2 indicated that there are two quenching processes which come from the excimer and monomer states. The short excimer lifetimes of 1 and 2 were ascribed to the energy transfer from the naphthyl moieties to the Ru centers. The different excimer ratio between 1 and 2 suggested that the excimer formation is affected by the conformation of the naphthyl moieties in the diruthenium(III) complexes.     

Characterization of a stable ruthenium complex with an oxyl radical

The ruthenium oxyl radical complex, [Ru(II)(trpy)(Bu(2)SQ)O(.-)] (trpy = 2,2':6',2"-terpyridine, Bu(2)SQ = 3,5-di-tert-butyl-1,2-benzosemiquinone) was prepared for the first time by the double deprotonation of the aqua ligand of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2) is reversibly converted to [Ru(III)(trpy)(Bu(2)SQ)(OH-)](+) upon dissociation of the aqua proton (pK(a) 5.5). Deprotonation of the hydroxo proton gave rise to intramolecular electron transfer from the resultant O(2-) to Ru-dioxolene. The resultant [Ru(II)(trpy)(Bu(2)SQ)O(.-)] showed antiferromagnetic behavior with a Ru(II)-semiquinone moiety and oxyl radical, the latter of which was characterized by a spin trapping technique. The most characteristic structural feature of [Ru(II)(trpy)(Bu(2)SQ)O(.-)] is a long Ru-O bond length (2.042(6) A) as the first terminal metal-O bond with a single bond length. To elucidate the substituent effect of a quinone ligand, [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) (4ClSQ = 4-chloro-1,2-benzosemiquinone) was prepared and we compared the deprotonation behavior of the aqua ligand with that of [Ru(III)(trpy)(Bu(2)SQ)(OH(2))](ClO(4))(2). Deprotonation of the aqua ligand of [Ru(III)(trpy)(4ClSQ)(OH(2))](ClO(4))(2) induced intramolecular electron transfer from OH- to the [Ru(III)(4ClSQ)] moiety affording [Ru(II)(trpy)(4ClSQ)(OH.)]+, which then probably changed to [Ru(II)(trpy)(4ClSQ)O(.-)]. The antiferromagnetic interactions (J values) between Ru(II)-semiquinone and the oxyl radical for [Ru(II)(trpy)(Bu(2)SQ)O(.-)] and for [Ru(II)(trpy)(4ClSQ)O(.-)] were 2J = -0.67 cm(-1) and -1.97 cm(-1), respectively.