Flow-injection photometric determination of nanogram levels of iron based on the catalysis of oxidative coupling of N-phenyl-p-phenylenediamine with m-phenylenediamine in a micellar medium

A highly sensitive photometric flow-injection method is described for the determination of iron(II, III) based on the catalytic action on the oxidative coupling of N-phenyl-p-phenylenediamine with m-phenylenediamine in the presence of hydrogen peroxide. The sensitivity of the method was enhanced by the addition of Tween 80 as a surfactant. The dynamic range was 0.5-30 ng/ml of iron(II, III) with the relative standard deviations below 3% at a sampling rate of 30 h(-1). The proposed method was subject to few interferences from coexisting metal ions and was successfully applied to the determination of iron in natural water samples.     

Catalytic determination of iodine in serum at nanogram levels using the As(III)/Ce(IV) reaction

Summary A catalytic determination of iodine using the As(III)/Ce(IV) reaction has been developed. The difference in reaction rate due to catalysis by iodide was measured spectrophotometrically at 310 nm. Optimum reaction conditions were investigated in order to obtain a greater sensitivity in the determination of iodine. The method can be satisfactorily used for samples containing iodine in the 0.4 to 10.0 ng range, with an overall error less than 6 %. The method has been used for the determination of iodine in serum, and gives results which compare favorably with a present clinical chemistry procedure.

---

Zusammenfassung Eine katalytische Jodbestimmungsmethode auf der Grundlage der As(III)/Ce(IV)-Reaktion wurde ausgearbeitet. Die durch Jodkatalyse bedingte Differenz des Reaktionsausmaßes wurde spektralphotometrisch bei 310 nm gemessen. Das Optimum der Reaktionsbedingungen für eine größtmögliche Empfindlichkeit der Jodbestimmung wurde ermittelt. Das Verfahren kann für Jodmengen zwischen 0,4 und 10,0 ng mit Erfolg verwendet werden; der durchschnittliche Fehler beträgt weniger als 6%. Jodbestimmungen im Serum nach dieser Methode stimmen mit klinisch-chemisch ermittelten Werten gut überein.

     

Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis

A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry.     

Catalytic determination of molybdenum in plants by flow-injection spectrophotometry with ion-exchange separation

The catalytic effect of molybdenum n the oxidation of iodide by hydrogen peroxide is utilized. A cation-exchange resin column is incorporated into the system to remove interfering ions; during sample processing, the interfering ions are eluted towards waste. Plant materials are ashed and solutions are injected. The proposed system can handle about 40 samples per hour with molybdenum contents in the 1.0–40.0 μg 1^?1 range. Results are precise (r.s.d. usually <%) and in agreement with those obtained by graphite-furnace atomic absorption spectrometry.     

Spectrophotometric determination of copper(II) at low mug l(-1) levels using cation-exchange microcolumn in flow-injection

A simple spectrophotometric flow-injection method is reported for the highly sensitive and fast determination of copper(II). The method is based on the formation of coloured Cu(II)-(4-methylpiperidinedithiocarbamate)(2) complex when the copper solutions are introduced into a tertiary reagent stream containing 4-methylpiperidinedithiocarbamate. The coloured complex is then selectively monitored at 435 nm. To increase interactions between copper(II) and colour forming reagent and preconcentrate of copper(II), a microcolumn containing strong cation exchange resins was placed between injection manifold and spectrophotometer. The system required no mixing chamber and allowed a sample throughput >60 sample h(-1). The calibration graph was linear in the range 5-100 mug l(-1). The detection limit was <0.5 mug l(-1) for 20 mul injection volume of copper(II) ion solution. The developed method was applied to environmental, copper processing water, and ore samples.     

Simultaneous catalytic-fluorimetric determination of copper and mercury by flow-injection analysis

Summary A catalytic-fluorimetric method is presented for the simultaneous determination of copper(II) and mercury(II) based on their catalytic effects on the oxidation of dipyridyldiketone phenylhydrazone and 2,2-dipyridylketone hydrazone, respectively, using the FIA/ stopped-flow mode. The errors in the determination of these cations are less than 10%, with a sampling rate of 45 samples per hour and the r.s.d. is 0.91% and 1.6% for Cu(II) and for Hg(II), respectively.

---

Simultane katalytisch-fluorimetrische Bestimmung von Kupfer und Quecksilber durch Flow-Injection-Analyse

Zusammenfassung Mit Hilfe der FIA/stopped-flow-Technik wurde eine Simultanbestimmung von Cu(II) und Hg(II) durchgeführt, die auf der katalytischen Wirkung dieser Elemente auf die Oxidation von Dipyridyldiketon-phenylhydrazon bzw. 2,2-Dipyridylketon-hydrazon beruht. Die Fehler sind geringer als 10% mit einem Probendurchsatz von 45 Proben je Stunde. Die relative Standardabweichung beträgt 0,91% für Cu und 1,6% für Hg.

     

Chemiluminescence determination of carbofuran at trace levels in lettuce and waters by flow-injection analysis

A simple, fast chemiluminescence (CL) flow-injection (FI) method based on the reaction of luminol with KMnO₄ in alkaline medium has been described for the direct determination of carbofuran. The method is based on the enhancing effect in the emission light from the oxidation of luminol produced in presence of carbofuran. The optimisation of instrumental and chemical variables influencing the CL response of the method has been carried out by applying experimental design, using the proposed flow-injection manifold. Under the optimal conditions, the CL intensity was linear for a carbofuran concentration over the range of 0.06-0.5 μg ml⁻¹, with a detection limit of 0.02 μg ml⁻¹. The method has been successfully applied to the determination of carbofuran residues in spiked water and lettuce samples.     

Quantitative determination of proteins at nanogram levels by the resonance light-scattering technique with macromolecules nanoparticles of PS-AA

The polystyrene-acrylic acid (PS-AA) nanoparticles have been prepared by ultrasonic polymerization, characterized by FT-IR and TEM. It is the first report on the determination of proteins with macromolecules nanoparticles of PS-AA by resonance light-scattering (RLS). At pH 6.9, the RLS of macromolecules nanoparticles of PS-AA can be enhanced by proteins. Based on this, a novel quantitative assay of proteins at the nanogram levels has been proposed. At pH 6.9, the RLS signals of PS-AA were greatly enhanced by proteins in the region of 250-700 nm characterized by the peak at 342 nm. Under optimal conditions, the linear ranges of the calibration curves were 0.02-11.0 microgml-1, 0.04-10.0 microgml-1 and 0.03-10.0 microgml-1 for gamma-globulin (gamma-IgG), bovine serum albumin (BSA) and human serum albumin (HSA), respectively. The detection limits were 16.0 ngml-1, 19.0 ngml-1, and 15.0 ngml-1 for gamma-IgG, BSA and HSA, respectively. The method has been applied to the analysis of total proteins in human serum samples collected from the hospital and the results were in good agreement with those reported by the hospital, which indicates that the method presented here is not only sensitive, simple, but also reliable and suitable for practical application.     

Bromide determination at nanogram levels by laser-excited molecular fluorescence spectroscopy in a graphite furnace

Bromide was determined at nanogram levels by introducing the sample with excess aluminum into a graphite furnace and measuring the laser-excited molecular fluorescence of aluminum bromide. Experimental parameters including excitation and fluorescence wavelengths, thermal conditions and aluminum concentration were optimized. Effects of concomitant ions and of barium hydroxide concentration, as a matrix modifier, have also been checked. The analytical reliability of the described procedure was checked by determining the bromide content in a standard reference material.     

A ring oven method for the determination of sulfate at nanogram levels

Summary A ring oven method for the determination of sulfate at ng levels is described. Sulfate is bound as 2-perimidinyl ammonium sulfate by spotting the sample solution on a glass fiber filter impregnated with 2-perimidinyl ammonium bromide. The excess reagent is removed by frontal elution chromatography with methanol and the sample spot cut out and then exposed to nitric acid vapor where upon the organic amine, bound as sulfate, is converted to the highly colored 2-amino 4,6,9-trinitro perimidine. The excess acid is neutralized by exposure to ammonia vapor. The sample spot is finally placed on a filter paper positioned on a ring oven and the color is eluted to the ring zone by successive aliquots of acetone. The sensitivity of the method is 5 ng sulfate and the working range is 20 ng to 1 g. The method is free of significant interferences.

---

Zusammenfassung Für die Bestimmung von Nanogramm-Mengen Sulfat wurde eine Ringofenmethode angegeben. Das Sulfat wird auf einem mit 2-Perimidinammoniumbromid imprägnierten Glasfaser-Filter durch Auftropfen der Probe als Salz der genannten Base gebunden. Der Reagensüberschuß wird elutionschromatographisch mit Methanol entfernt, der Probefleck ausgeschnitten und Salpetersäure-Dämpfen ausgesetzt, wobei die organische Base, die als Sulfat gebunden war, in das stark gefärbte 2-Amino-4,6,9-trinitroperimidin übergeht. Die überschüssige Säure wird mit Ammoniakdämpfen gebunden. Schließlich wird der Probefleck auf einen Ringofen gebracht und mit Aceton in den Ring gewaschen. Die Empfindlichkeit der Methode beträgt 5 ng Sulfat, der geeignete Arbeitsbereich erstreckt sich von 20 ng bis 1 g. Die Methode unterliegt keinen Störungen.

     

Determination of copper at ng levels by in-line preconcentration and flow-injection analysis coupled with flame atomic-absorption spectrometry

Oxine/formaldehyde/resorcinol and oxine/formaldehyde/hydroquinone resins have been synthesized and their physicochemical properties studied. Conditions were optimized for the preconcentration of copper by batch extraction and column chromatography with the resins. A flow-injection analysis (FIA) manifold was constructed for the determination of copper at ng levels by preconcentration on microcolumns containing the resins, stripping, and atomic-absorption spectrometry. For batch preconcentration a pH of about 2.5-3 was optimal whereas in the FIA system a broader pH range (approximately 2-3.5) could be used. Separations of binary mixtures of Cu(II) with Ni(II) or PB(II) at microg/ml level did not show any cross-contamination. In the FIA, a 2 cm long column and 2 ml/min flow-rate were adequate for quantitative uptake of copper; 50 micro1 of 0.1M hydrochloric acid quantitatively eluted the copper.     

Enhanced surfactant determination by ion-pair formation using flow-injection analysis and dynamic surface tension detection

Chemical analysis of surface active species (surfactants) is of interest for many applications, such as in process monitoring, biomedical applications, environmental monitoring and surface science investigations. Recently, we reported a dynamic surface tension detector (DSTD) based upon optically probing the size of a repeating drop resulting from constant flow of an aqueous solvent out of the end of a capillary. Presence of a surfactant in a growing drop reduces the surface tension at the air-solvent interface, causing the drop to detach at a smaller volume, which is detected. The DSTD has a kinetic dependence, and with increasing flow rate the sensitivity decreases due to diffusional and adsorption effects. We report that for the sodium salt of dodecylsulfate (DS), the DSTD performs significantly better with a stainless steel (S.S.) capillary dropper than with a fused silica dropper because the S.S. dropper exhibits a smaller adsorption effect as a function of time. Flow-injection analysis with the DSTD of DS was found to enhance sensitivity 50-fold by in-situ reaction with the ion-pair reagent tetrabutylammonium hydroxide (TBA) in water, even though the TBA alone was not very surface active. The TBA-DS system serves as a model for a selective detection method in which surface activity is exploited and enhanced. The detection limit for DS, as TBA-DS, was 400 ppb. Additionally, weakly surface active species such as TBA could be analyzed "indirectly" by ion-pair formation with DS. The enhanced sensitivity is due to increased packing of the ion-pairs at the air-aqueous solvent interface. The flow rate dependence on the sensitivity of detecting the TBA-DS ion-pair was examined. Two limiting conditions were observed as a function of ion-pair concentration: sensitivity decreases linearly with inverse flow rate at high flow rates and approaches a steady state at slower flow rates.     

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.     

Determination of arsenic in the presence of high copper concentrations using flow-injection analysis-hydride atomic absorption spectrometry

Summary Arsenic is determined in environmental samples containing metal ions up to 10,000 mg/l copper, 200 mg/l lead, 200 mg/l iron and 200 mg/l nickel by using the FIA-hydride-AAS technique. In the presented sample preparation method arsenic is prereduced and the interfering metal ions are precipitated. As signal depressions from metal ions are excluded, a detection limit of 1 g/l arsenic is achieved.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Quantitative determination of proteins at nanogram levels by the resonance light-scattering technique with composite nanoparticles of CdS/PAA

This paper describes the development of composite nanoparticles. A novel composite nanoparticle has been prepared by an in situ polymerization method. The nano-CdS has been prepared, then the polymerization of acrylic acid (AA) was carried out by initiator potassium persulfate (KPS) under ultrasonic irradiation. The surface of the composite nanoparticles was covered with abundant carboxylic groups (-COOH). The nanoparticles are water-soluble, stable and biocompatible. Reaction of the composite nanoparticles with proteins results in an enhanced resonance light scattering (RLS) at 380 nm. Based on this, a new resonance light-scattering (RLS) method was developed for the determination of proteins including BSA, HSA and human gamma-IgG. Under the optimum conditions, the enhanced RLS intensity is linearly proportional to the concentration of proteins. The liner range is 0.1-15 microgmL(-1) for HSA, 0.2-20 microgmL(-1) for BSA and 0.1-50.0 microgmL(-1) for human gamma-IgG, respectively. The method has been applied to the determination of the total protein in human serum samples collected from the hospital and the results are in good agreement with those reported by the hospital. This method proved to be very sensitive, rapid, simple and tolerant of most interfering substances.     

Univariate and simplex optimization for the flow-injection spectrophotometric determination of copper using nitroso-R salt as a complexing agent.

A simple colorimetric flow-injection system for the determination of Cu(II) based on a complexation reaction with nitroso-R salt is described. The chemical and FIA variables were established using the univariate and simplex methods. A small volume of Cu(II) was mixed with merged streams of nitroso-R salt and acetate buffer solutions. The absorbance of the complex was continuously monitored at 492 nm. The calibration curve over the concentration range 1.0-7.0 microg ml(-1) was obtained. The relative standard deviation for determining 4.0 microg ml(-1) Cu(II) was 0.47% (n = 11). The detection limit (3sigma) was 0.68 microg ml(-1) and the sample throughput was 150 h(-1). The validity of the method has been satisfactorily examined for the determination of Cu(II) in wastewater and copper ore samples. The accuracy was found to be high, because the student t-values were calculated to be less than the theoretical values when the results were compared with those obtained by FAAS.     

Liquid chromatographic determination of aniline and derivatives in environmental waters at nanogram per litre levels using fluorescamine pre-column derivatization

Summary Fluorescamine (fluram) has been used as a fluorogenic compound for pre-column derivatization of aniline and some derivatives. Anilines were derivatized with fluram in citrate buffer media (pH 5.5) to form pyrrolinones. The highly fluorescence pyrrolinones were isolated and pre-concentrated by solid phase extraction. A reversed phase, Spherisorb RP-8 column and tetrahydrofuran: water:formic acid (42:56:2) mobile phase was used for separation. Detection method was by a sensitive fluorimetric method and quantitation was at 395 and 495 nm. The various parameters such as reaction conditions between anilines and fluram, solid phase extraction and chromatographic separation were optimized. Calibrations were linear over the range considered with excellent correlation coefficients (r>0.999). Relative standard deviations are less than 2.5 % and detection limits for aniline,p-toluidine, 4-chloroaniline and 4-bromoaniline were 6, 30, 6 and 8 ng L⁻¹, respectively. This method has been used successfully for the determination of anilines in environmental waters.     

Catalytic flow-injection determination of sub-ppb copper(II) using the redox reaction of cysteine with iron(III) in the presence of 2,4,6-tris(2-pyridyl)-1,3,5-triazine.

A kinetic-catalytic spectrophotometric flow-injection method was developed for the rapid and sensitive determination of trace amounts of copper(II). The method is based on the catalytic effect of copper(II) on the redox reaction of cysteine with iron(III). Iron(II) produced by the catalytic reaction reacts with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) to form the iron(II)-TPTZ complex (lambda(max) = 593 nm). By measuring an absorbance of the complex, one could determine 0.05-8 ppb copper(II) with the relative standard deviations (n = 10) of 1.6%, 1.3%, and 0.8% for 0.5 ppb, 1 ppb, and 2 ppb copper(II), respectively. The limit of detection (S/N = 3) was 0.005 ppb. The sample throughput was 30 h(-1). The proposed method was successfully applied to the determination of copper in natural water and serum samples.     

Selective flow-injection determination of residual chlorine at low levels by amperometric detection with two polarized platinum electrodes

Flow-injection amperometry with two polarized platinum electrodes is used for the determination of residual chlorine based on the oxidation of iodide. Interferences of iron(III), copper(II), nitrite and atmospheric oxygen are eliminated in the proposed procedure. The detection limit for residual chlorine is 2 μg l^?1 at a sampling rate of 120 h^?1; linear calibration graphs are obtained up to 0.8 mg 1^?1. A method for the simultaneous flow-injection determination of residual chlorine and copper(II) is also proposed.