A very sensitive flow system for the direct determination of copper in natural waters based on spectrophotometric detection

A very sensitive flow injection method with spectrophotometric detection has been developed for the on-line determination of copper in natural waters. The method exhibits a limit of detection three times lower than the most sensitive direct spectrophotometric method previously described and then allows the direct and simple in situ determination of copper in most natural waters.The method was based on the measurement of the absorbance of the coloured complex formed by copper with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. This complex presents stoichiometry 1:2 (Cu:dPKBH), and exhibits maximum absorbance at 370 nm. The manifold used was very simple, and consisted of two channels. The first one contained the sample while the second one contained the colorimetric reagent (3.3×10⁻⁴ M dPKBH in 10% ethanol), in a 1.6×10⁻² M phosphate buffer solution at pH 8. The performance of the system was optimised by using both univariate and modified simplex methodologies. When modified simplex was used, the best signal was obtained for a sample injection volume of 529 μl, a reaction coil length of 1.29 m, and a reagent flow rate of 4.8 ml min⁻¹. Under optimum conditions, the response was linear up to 3 mg l⁻¹ copper, the equation of the straight line being y=0.314x+5.2×10⁻⁴ (r²=0.998). The method allowed a sampling frequency of 40 samples per hour and exhibited a precision of 2.11% (as R.S.D., n=11). The limit of detection was 4.6 μg l⁻¹ (calculated as 3s_b/m, where s_b is the standard deviation of the y-intercept and m represents the slope of the straight line), and was therefore more sensitive than all the direct continuous methods reported previously.The method was successfully applied to the analysis of real water samples, with an average relative error of 5.32%.     

Design of two channel flow cells for simultaneous determination of copper and iron

Two compact double and serial flow cells were designed for simultaneous determination of trace copper and iron ions. 2-(5-Bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)aniline(5-Br-PSAA) was used as a chromogenic reagent. 5-Br-PSAA reacted with Cu(II) and Fe(II) to form red chelate compounds and did not react with Cu(I) and Fe(III). Based on these characteristics, a three-lines flow system using two channel flow cells was assembled for the simultaneous determination of trace amounts of copper and iron and applied to the assay of ground water.     

A simple and selective flow-injection spectrophotometric determination of copper(II) by using acetylsalicylhydroxamic acid

A new simple, and rapid flow-injection spectrophotometric method is developed for the determination of trace amounts of Cu(II) by using a new chromogenic reagent acetylsalicylhydroxamic acid (AcSHA). The method is based on the formation of colored Cu(II)-(AcSHA)₂ complex. The optimum conditions for the chromogenic reaction of Cu(II) with AcSHA is studied and the colored (green) complex is selectively monitored at λ_max 700 nm. With the reagent carrier solvent (dimethylsulfoxide (DMSO) and acetate buffer, pH 4.2) flow-rate of 1 ml min⁻¹, a detection limit (2S) of 1 μg l⁻¹ Cu(II) was obtained at a sampling rate of 80 sample h⁻¹. The calibration graph was linear in the Cu(II) concentration range 5-120 μg l⁻¹. The relative standard deviation (n=10) was 0.64% for a sample containing 60 μg l⁻¹ Cu(II). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied to determine trace amounts of copper(II) in river and seawater samples. The accuracy of the method was demonstrated by the analysis of standard reference materials C12X3500 and C14XHS 50.     

Kinetic method for determination of nanogram amounts of copper(II) by its catalytic effect on hexacynoferrate(III)-citric acid indicator reaction

This paper describes a highly sensitive, selective catalytic-kinetic-spectrophotometric method for the determination of copper(II) concentration as low as 6 ng ml⁻¹. The method is based on the catalytic effect of copper(II) on the oxidation of citric acid by alkaline hexacyanoferrate(III). The reaction was followed by measuring the decrease in absorbance of hexacyanoferrate(III) at 420 nm (λ_max of [Fe(CN)₆]³⁻, ∈ = 1020 dm³ mol⁻¹ cm⁻¹). The dependence of rate of the indicator reaction on the reaction variables has been studied and discussed to propose a suitable mechanism to get a relation between the reaction rate and [Cu²⁺]. A fixed time procedure has been used to obtain a linear calibration curve between the initial rate and lower [Cu²⁺] or log[Cu²⁺] in the range 1 × 10⁻⁷ to 4 × 10⁻⁴ mol l⁻¹ (6.35-25,400 ng ml⁻¹). The detection limit has been calculated to be 4 ng ml⁻¹. The maximum average error is 3.5%. The effect of the presence of various cations, commonly associated with copper(II) and some anions has also been investigated and discussed. The proposed method is sensitive, accurate, rapid and inexpensive compared to other techniques available for determination of copper(II) in such a large range of concentration. The new method has been successfully applied for the determination of copper(II) in various samples.     

Kinetic-catalytic determination of traces of iron by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline

A new kinetic-catalytic method by the initial rate procedure for the determination of nanogram level of iron(III) is developed, which is based on its catalytic effect on the oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an indamine dye (λ_max=590 nm) in the presence of hydrogen peroxide. Iron(II) is also determined, being oxidized to iron(III) by hydrogen peroxide. Calibration graphs obtained by the initial rate method are linear in the range 1–1000 ng ml⁻¹ Fe and as low as 10⁻⁸ M Fe(II, III) can easily be determined. The relative standard deviations are 6.6, 2.5 and 1.5% for ten determinations of 1, 20 and 60 ng ml⁻¹ of Fe(III), respectively. The method is applicable to the determination of iron in natural waters without preconcentration and separation.     

偏最小二乘分光光度法同时测定痕量铁、锰、铜、锌、钴和镍

痕量Fe^3 ,Mn^2 ,Cu^2 ,Zn^2 ,Co^2 ,Ni^2 与2－（5－溴－2－吡啶偶氮）－5－二乙氨基苯酚（5－Br-PADAP)和溴化十六烷基三甲基铵（CTMAB）在PH8．3时发生高灵敏显色反应，所形成的三元胶束络合的吸收光谱严重重叠，采用偏最小二乘法（PLS）辅助分光光度法测定了合成试样及饲料中上述6种痕量组分，结果表明，PLS法是化学计量学中一种可适用于基体较复杂的实际试样中痕量组分分光度同时测定的多元计算方法。     

Quantitative determination of iron and copper in cotton material by TLC

Summary A TLC method for the separation of quantitative determination of copper and iron in cotton material is described. The optimal solvent system is 9:2:1 (v/v), ethanol-nitric acid-hydrochloric acid and the locating reagent is Na-diethyldithiocarbamate. Regression analysis shows that the most precise results can be obtained for the concentration range of 0.0400–0.0800 mg/ml of iron and copper.     

Extraction-liquid chromatography with electrochemical and spectrophotometric detection for the determination of copper and iron in biological and river water samples

Reversed-phase liquid chromatography using cupferron as a precolumn derivatizing agent was developed for the determination of Cu(II) and Fe(III) in biological materials and natural water samples. In the direct method, the metal cupferronates formed in acetonitrile-water (1 + 1) are injected onto an ODS column followed by separation with a mobile phase containing acetonitrile-acetate buffer (pH 3.5) (7 + 3) and other reagents. Amperometric detection with a glassy carbon electrode at ?0.40 V vs. Ag/AgCl can be used to determine both metals simultaneously. The electrochemical detection method has better sensitivity for the determination of Fe(III) than the usual spectrophotometric detection at 375 nm. If a large volume of aqueous sample is available, concentration of the two metal ions can be made by extraction with ethyl acetate prior to the chromatographic determination. In this case, liquid chromatographic separation and determination can be performed with the ODS column using a mobile phase consisting of acetonitrile-methanol-ethyl acetate-0.02 M acetate buffer (pH 3.5) (45 + 20 + 5 + 30).     

Application of a poly(dithiocarbamate) resin to the determination of trace copper,iron and zinc in natural waters

A chelating poly(dithiocarbamate) resin with macroreticular support is shown to be effective for the preconcentration of copper, iron and zinc in natural waters. The retained ions can be eluted efficiently in 5 ml of 8M nitric acid from 1–20-cm columns of resin.This poly(dithiocarbamate) resin is used for the preconcentration and determination of copper, iron and zinc by flame atomic absorption spectrophoto-metry. Common ions present in natural waters do not interfere. The detection limits were 0.50, 0.21 and 0.04 g 1^–1 for Cu, Fe and Zn respectively.     

A multicommuted flow system for the determination of copper, chromium, iron and lead in lubricating oils with detection by flame AAS

In this work, a flow analysis procedure for the determination of copper, chromium, iron and lead in lubricating oils using flame AAS as detection technique is described. The flow manifold was designed to implement the multicommutation approach and it comprised three 3-way solenoid valves controlled by a personal computer. The flow system presented allowed to process the oil samples to determine wear metals without any prior preparation. Aiming to assess accuracy the results were compared with those obtained by manual procedure using flame AAS. Applying the joint-confidence ellipse test, no significant difference at the 95% confidence level was observed. Other profitable features such as a sample throughput of 50 determinations per hour; relative standard deviations (n = 5) below 2% for Cu, and below 8% for Cr, Fe and Pb; and linear responses in the range 0–40 ppm (w/w) (Cu, Fe) and 0–15 ppm (w/w) (Cr, Pb) were also achieved.     

Simple and rapid catalytic spectrophotometric determination of superoxide anion radical and superoxide dismutase activity in natural medical vegetables using phenol as the substrate for horseradish peroxidase

The coupling reaction of 4-aminoantipyrine (4-AAP) with phenol using the superoxide anion radical ( ) as oxidizing agent under the catalysis of horseradish peroxidase (HRP) was studied. Based on the reaction, produced by irradiating vitamin B₂ (V_B2) was spectrophotometrically determined at 510 nm. Under the optimum experimental conditions, the relationship between A ₅₁₀ and concentration was linear in the range 9.14×10^–6–1.2×10^–4 mol L^–1. The detection limit was determined to be 1.37×10^–6 mol L^–1. A possible reaction mechanism was discussed. The effect of interferences and surfactants on the determination of was also investigated. The proposed method was applied to determine superoxide dismutase activity in garlic, scallion, and onion with satisfactory results.     

Analytical properties of 1-phenyl-1,2-propanedione-2-oxime thiosemicarbazone: simultaneous spectrophotometric determination of copper(II) and nickel(II) in edible oils and seeds

The analytical properties of 1-phenyl-1,2-propanedione-2-oxime thiosemi-carbazone (PPDOT) are described for the first time. The reagent gives colour reactions with copper(II) and nickel(II) in sodium acetate-acetic acid buffer medium. The copper complex shows maximum absorbance at 465 nm while the nickel complex at 395 nm. Therefore, these colour reactions have been advantageously used for the simultaneous spectrophotometric determination of copper(II) and nickel(II) in synthetic mixture and also in edible oils and seeds.     

Comparison of slurry sampling and microwave-assisted digestion for calcium, magnesium, iron, copper and zinc determination in fish tissue samples by flame atomic absorption spectrometry

The development of a slurry sampling method for the determination of calcium, copper, iron, magnesium and zinc in fish tissue samples by flame atomic absorption spectrometry is described. In comparison with microwave-assisted digestion, the proposed method is simple, requires short time and eliminates total sample dissolution before analysis. Suspension medium was optimized for each analyte to obtain quantitative recoveries from fish tissue samples without matrix interferences. Nevertheless, iron recoveries higher than 46% were not found. Treatment of samples slurried in nitric acid by microwave irradiation for 15-30 s at 75-285 W permitted to achieve efficient recoveries for calcium, iron, magnesium and zinc. Further improvement in the matrix effects for iron determination was accomplished by the use of an additional step of short microwave-assisted suspension treatment. However, standard addition method was required for calcium and copper determination, being necessary hydrochloric acid as suspension medium for the last one. Although copper could not be determined in the certified reference material using microwave-assisted digestion, the accuracy of the slurry sampling method was verified for all the investigated analytes. Detection limits were 22.8 ± 8.0, 0.884 ± 0.092, 5.07 ± 0.76, 35.5 ± 0.7 and 1.17 ± 0.04 μg g⁻¹ for calcium, copper, iron, magnesium and zinc, respectively. The standard deviations obtained using slurry sampling method and microwave-assisted digestion were not significantly different, and the mean relative standard deviation of the over-all method (n = 3) of the slurry sampling method for different concentration levels was below 12%.     

Use of radiation sources with mercury isotopes for real-time highly sensitive and selective benzene determination in air and natural gas by differential absorption spectrometry with the direct Zeeman effect

A new analytical portable system is proposed for the direct determination of benzene vapor in the ambient air and natural gas, using differential absorption spectrometry with the direct Zeeman effect and innovative radiation sources: capillary mercury lamps with different isotopic compositions (¹⁹⁶Hg, ¹⁹⁸Hg, ²⁰²Hg, ²⁰⁴Hg, and natural isotopic mixture). Resonance emission of mercury at a wavelength of 254 nm is used as probing radiation. The differential cross section of benzene absorption in dependence on wavelength is determined by scanning of magnetic field. It is found that the sensitivity of benzene detection is enhanced three times using lamp with the mercury isotope ²⁰⁴Hg in comparison with lamp, filled with the natural isotopic mixture. It is experimentally demonstrated that, when benzene content is measured at the Occupational Exposure Limit (3.2 mg/m³ for benzene) level, the interference from SO₂, NO₂, O₃, H₂S and toluene can be neglected if concentration of these gases does not exceed corresponding Occupational Exposure Limits. To exclude the mercury effect, filters that absorb mercury and let benzene pass in the gas duct are proposed. Basing on the results of our study, a portable spectrometer is designed with a multipath cell of 960 cm total path length and detection limit 0.5 mg/m³ at 1 s averaging and 0.1 mg/m³ at 30 s averaging. The applications of the designed spectrometer to measuring the benzene concentration in the atmospheric air from a moving vehicle and in natural gas are exemplified.     

Effect of ion-pairing modifiers in the separation of cobalt,copper, iron,and palladium by pre-column derivatization and high performance liquid chromatography

Summary Multivariate experiment analyses have been used to determine the behaviour, in high-performance liquid chromatography, of cobalt, copper, iron and palladium complexes with 1-nitroso-2-naphthol-6-sodium sulphonate or 2-nitroso-1-naphthol-6-sodium sulphonate ion-associated before injection or during elution with quaternary ammonium salts, namely TDTMABr, CTMABr, and TDDMBACl.The role of the ion-pairing modifiers was to regulate the capacity factors of the complexed metals. The work-up procedures showed that the elution and separation of the metal complex anions were influenced by the concentration and choice of cationic counter compounds. TDTMABr, CTMABr and TDDMBACl were replaced with inorganic salts, such as sodium sulphate, but there was no evidence of better metal separation than with the organic compounds.The studies showed that complexed metal ions can be separated using endcapped silica or polymer as column packing materials. The result of most-potential value was that gradient elution could be used to minimize retention without dissocation of the ion-associates on the column.     

Simultaneous spectrophotometric determination of iron and vanadium by H-point standard addition method and partial least squares regression in micellar medium

Simultaneous determination of total iron and vanadium by H-point standard addition method (HPSAM) and partial least squares (PLS) is described. Gallic acid (GA) in a cationic micellar solution of CTAB was used for determination of iron and vanadium in different oxidation states at pH 5. The presence of a micellar system enables total iron and vanadium to be determined with improved sensitivities. The total relative standard error for applying the PLS method to 15 synthetic samples in the ranges 0.20–15.00 μg ml⁻¹ iron and 0.20–8.00 μg ml⁻¹ vanadium was 2.2%. The results of applying the H-point standard addition method showed that iron and vanadium can be determined simultaneously with the concentration ratios of iron to vanadium from 10:1 to 1:20 in the mixed sample. Both HPSAM and PLS methods showed suitable abilities to resolve accurately overlapped absorption spectra of the compounds. Both proposed methods were successfully applied to the determination of Fe and V in several synthetic alloy solutions.     

2,2′-Dihydroxybenzophenone thiosemicarbazone as a spectrophotometric reagent for the determination of copper,cobalt, nickel,and iron trace amounts in mixtures without previous separations

2,2′-Dihydroxybenzophenone thiosemicarbazone forms complexes with Cu(II) (λ_max = 385 nm, ? = 8.60 × 10³ liter · mol^?1 · cm^?1); Ni(II) (λ_max = 380 nm, ? = 15.4 × 10³ liter · mol^?1 · cm^?1); Co(II) (λ_max = 380 nm, ? = 12.3 × 10³ liter · mol^? · cm^?1); and Fe(III) (λ_max = 365 nm, ? = 7.9 × 10³ liter · mol^?1 · cm^?1) and have been applied to the analysis of these metal ions in binary, ternary, and quaternary mixtures. The determination procedures are based exclusively on the different pH values of the formation complexes, hence the extraction step is not necessary.     

Continuous sonoassisted digestion coupled to flow injection minicolumn separation for the determination of total and labile Cu and Fe in fresh waters by flame atomic absorption spectrometry

An automatic on-line system is developed for the trace determination of copper and iron species in fresh waters by flame atomic absorption spectrometry using only 5 and 2?mL of sample, for copper and iron determination, respectively. This system, which includes a home-made minicolumn of commercially available resin containing aminomethylphosphonic acid functional groups (Chelite P), comprises two operational modes. The first, used for the determination of the dissolved labile fraction (free copper and iron ions and their weak complexes) is based on the elution of this fraction from a minicolumn containing the chelating resin loaded in-situ with the sample. The second mode is used for the determination of total trace copper and iron concentrations. This last mode is based on the retention/preconcentration of total metals on the Chelite P resin after on-line sonoassisted digestion of water samples acidified with nitric acid (0.5?mol?L^?1 final concentration) to break down metal organic complexes present in fresh waters as river waters. The figures of merit for copper and iron determination in both fractions are given and the obtained values are discussed. The analytical method was characterized and the limit of detection and limit of quantification for the two metals were 0.5 and 1.6?µg?L^?1 for Cu and 2.3 and 6.1?µg?L^?1 for Fe, respectively. The repeatability, expressed as relative standard deviation, was in the range 1.0–2.1%. The speciation scheme was applied to the analysis of river surface water samples collected in Galicia (Northwest, Spain).