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.     

Direct chlorine determination in crude oils by energy dispersive X-ray fluorescence spectrometry: An improved method based on a proper strategy for sample homogenization and calibration with inorganic standards

Official guidelines to perform chlorine determination in crude oil are (i) American Society for Testing and Materials (ASTM) D6470, which is based on the extraction of water from the oil and subsequent determination of the chloride by potentiometry, (ii) ASTM D3230, that measures the conductivity of a solution of crude oil in a mixture of organic solvents and (iii) US Environmental Protection Agency (EPA) 9075 that uses energy dispersive X-ray fluorescence spectrometry to quantify chlorine and it is applicable for the range from 200 μg g^− 1 to percent levels of the analyte. The goal of this work is to propose method to quantify lower amounts of chlorine in crude oil using energy dispersive X-ray fluorescence spectrometry using a simple calibration strategy. Sample homogenization procedure was carefully studied in order to enable accurate results. The calibration curve was made with standards prepared by diluting aqueous NaCl standard in glycerin. The method presented a linear response that covers the range from 8 to at least 100 μg g^− 1 of chlorine. Chlorine in crude oil samples from Campos Basin - Brazil were quantified by the proposed method and by potentiometry after extraction of chlorine from the oil. Results achieved using both methods were statistically the same at 95% confidence level.     

Trace determination of gaseous chlorine: a comparison between an electrometric method and the methyl orange photometric method

Two methods for the determination of molecular chlorine in air are critically compared. An electrometric method based on measurement of the reduction current of chlorine to chloride is superior to the photometric determination based on bleaching of an acidic solution of methyl orange. The limit of detection for the electrometric method is 50 μg m^-3; the standard error of the mean is better than 2%, and the sensitivity is 5.9 μg m^-3 μ A^-1 at +50 mV applied potential versus SCE with a mercury cathode. The limit of detection for the photometric method is 300 μg m^-3; the precision is of the order of 5%, and the sensitivity is 80 μg m^-3 for an error of 1% in the absorption measurements. The accuracy of the electrometric method is good whereas the photometric method yields consistently low results. The electrometric method is less subject to interferences than the photometric method.     

A new sensitive and selective fluorescence method for determination of chlorine dioxide in water using rhodamine S

A new simple, selective and sensitive method for the determination of trace chlorine dioxide in water has been developed, based on the oxidation by chlorine dioxide to reduction the fluorescence of rhodamine dyes in ammonia-ammonium chloride buffer solution. Four rhodamine dyes systems such as rhodamine S, rhodamine G, rhodamine B and butyl-rhodamine B were tested. The rhodamine S system is the best, with a linear range of 0.0060-0.450 μg mL⁻¹ and a detection limit of 0.0030 μg mL⁻¹ ClO₂. It was applied to the determination of chlorine dioxide in synthetic samples and real samples, with satisfactory results. This method has good selectivity, especially, other chlorine species such as chlorine, hypochlorite, chlorite and chlorate do not interfere the determination. The mechanism of fluorescence reduction was also considered.     

Measurements of the apparent rate constant for the reaction of iodine monoxide with chlorine monoxide to form iodine atoms

An apparatus for measuring the resonance fluorescence signals of iodine and chlorine atoms is constructed to study iodine monoxide reaction with chlorine monoxide. A technique using the reaction of chlorine atoms with C₂H₆ is developed to calibrate the sensitivity of the apparatus to chlorine atoms. The apparent rate constants for the reaction between 10^• and CIO^• radicals producing iodine atoms was measured at 295 K k_app = (2.62 ± 0.57) x 10-^-11 cm³ molecule^-1 s^-1.     

Gas diffusion sequential injection system for the spectrophotometric determination of free chlorine with o-dianisidine

A gas diffusion sequential injection system for spectrophotometric determination of free chlorine is described. The detection is based in the colorimetric reaction between free chlorine and a low toxicity reagent o-dianisidine. A gas diffusion unit is used to isolate free chlorine from the sample in order to avoid possible interferences. This feature results from the conversion of free chlorine to molecular chlorine (gaseous) with sample acidification. With minor changes in the operating conditions, two different dynamic ranges were obtained enhancing the application both to water samples and bleaches. The results obtained with the developed system were compared to the reference method, iodometric titration and proved not to be statistically different. A detection limit of 0.6 mg ClO⁻/L was achieved. Repeatability was evaluated from 10 consecutive determinations being the results better than 2%. The two dynamic ranges presented different determination rates: 15 h⁻¹ for 0.6-4.8 mg ClO⁻/L (water samples) and 30 h⁻¹ for 0.047-0.188 g ClO⁻/L (bleaches).     

Potentiometric flow-injection determination of trace chlorine based on its redox reaction with an iron(III)/iron(II) buffer

A very sensitive and rapid potentiometric determination of trace chlorine in water is described. The method is based on the transient potential changes which appears during the reduction of dissolved chlorin with an iron(III)/iron(II) potential buffer containing chloride and sulfuric acid. The sample is injected into a water carrier stream and merged with a stream of this potential buffer solution; chlorine is reduced during passage through a short reaction coil. The potential change from the baseline is measured with a flow-through ORP (oxidation-reduction potential) electrode. Potential changes (peak heights) are proportional to chlorine concentrations from 10^?7 M to 10^?5 M. The detection limit is 5 × 10^?8 M (3.5 μgl^?1 as Cl₂). The sample throughput is 45 h^?1. Reproducibility is in the range 2.5–1.1%. Results for potable water agree with those obtained by the o-tolidine method.     

Xanthene Dye Chemiluminescence for Determination of Free Chlorine in Water

Abstract

Preliminary investigations by a batch method are described for aiming at the flow determination of free chlorine in water with novel chemiluminescence (CL) detection. The CL originates from the reaction of xanthene dyes with free chlorine, Cl₂, HOCl, and OCl^?. Through the measurements of CL decay curves, fundamental CL characteristics were explored from the analytical point of view. Among xanthene dyes tested, eosin Y. eosin B. pyronin B. and rhodamine 6G were found to be promising CL reagents with such sensitivity and selectivity that free chlorine can be readily determined in tap water. In particular. these CL systems have the special advantage of being insensitive to oxo acids of chlorine and chloramine. Recommended flow systems are proposed.     

Linear-sweep polarographic determination of active chlorine in aqueous solutions containing phenylthiourea

The linear-sweep polarographic determination of active chlorine is based on its reaction with phenylthiourea in acidic phosphate buffer (pH 2.5) containing potassium chloride. The product, C,C-diphenyldithiodiformamidine, is strongly adsorbed and then reduced at a mercury electrode with two peaks at about ?0.35 V and ?0.87 V (vs. SCE). In the presence of 0.05 M potassium chloride, the potential of the first peak shifts positively to ?0.31 V. This peak provides high sensitivity and selectivity for the determination of traces of active chlorine. The linear range is 1×10^?7?2.5×10^?5 M and the detection limit is 5×10^?8 M (3.6 μg l^?1). The method is used for the direct determination of active chlorine in tap water. The mechanism of the reaction was studied by cyclic voltammetry, electrolysis and potentiometric titration. The first peak (?0.35 V) is ascribed to the reduction of a mercury (II) sulfide film produced by reaction of the adsorbed dithio product with mercury. In the presence of 0.05 M chloride, the formation of a mixed HgS·xHg₂Cl2 film shifts the peak to ?0.31 V.     

Isotropic and anisotropic chlorine hyperfine coupling of dichloro-dicyano benzoquinone anion radical

The ESR spectrum of 2,3-dichloro-5,6-dicyano benzoquinone anion has been recorded in the isotropic and in the nematic phase of liquid crystal solvents. In the isotropic phase it shows splitting only by two ¹⁴N nuclei, while in the nematic phase at high orientation degree, the pattern is that expected for hyperfine coupling with two chlorine nuclei. The orientation of the free radical in the nematic solvent is inferred from the variation of the ¹⁴N splitting.The chlorine anisotropic coupling is used to get the unpaired electron spin density on the chlorine π orbital and the isotropic coupling is discussed in terms of a relationship analogous to that proposed by Karplus and Fraenkel for ¹³C.     

Measurement of concentration of chlorine attached to a stainless-steel canister material using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) in the single-pulse or orthogonal double-pulse configuration was performed for the measurement of the concentration of chlorine, which induces the occurrence of stress corrosion cracking (SCC), attached to stainless-steel (UNS S30403). The chlorine spectra were measured for samples sprayed with synthetic seawater with chlorine concentrations from 0.1 to 1.0 g/m². The chlorine emission intensity decreased between chlorine concentrations of 0.4 and 1.0 g/m² as determined in the single-pulse measurement. The chlorine concentration dependence of the chlorine emission intensity in the single-pulse configuration was unchanged even when the laser energy was set between 30 and 100 mJ. On the other hand, the chlorine emission intensity increased linearly versus chlorine concentration from 0.1 to 1.0 g/m² with the orthogonal double-pulse configuration. The results suggest that LIBS is promising for the inspection of the environmental condition for SCC initiation, which can occur when the chlorine concentration is greater than or equal to 0.8 g/m².     

Determination of chlorine distribution in silicon dioxide by neutron activation

A neutron activation method for the determination of chlorine distribution in silicon dioxide on the surface of Si wafers has been developed. After irradiation of the sample with a standard, successive layers are removed from the oxide surface by chemical etching and the chlorine content in the solutions obtained is determined gamma-spectrometrically. Using a Ge(Li) detector, a lower limit of determination of 1.0·10⁻⁷ g was obtained. This limit can be improved by using a NaI(Tl) detector. The error of chlorine determination is discussed.     

Flow injection analysis system based on amperometric thin-film transducers for free chlorine detection in swimming pool waters

This work reports on the performance of a user-friendly flow injection analysis (FIA) system for the monitoring of free chlorine. A methacrylate flow cell integrating a gold thin-film microelectrode, together with an on-chip gold counter electrode, both fabricated by microfabrication technology, provided robustness, low output impedance, rapid response and low cost to the proposed flow system. An external Ag/AgCl reference electrode placed downstream the chip completes the electrochemical cell. Amperometric detection of chlorine was carried out at a set potential of +350 mV, without oxygen interference. The proposed flow system responded linearly to chlorine concentrations in a range from 0.2 to 5 mg l⁻¹, with a sensitivity of 0.23 μA l mg⁻¹, the estimated limit of detection being 0.02 mg l⁻¹. In addition, the system response was kept stable for at least 10 days (±3σ criterion), by keeping the flow system in an inert atmosphere when not in use. Fifteen samples of swimming pool waters were analyzed and no matrix effects were detected. Also, results were in good agreement with those obtained by a standard method. The excellent analytical performance of the system together with its good working stability would also enable its application for the detection of chlorine in other matrices such as tap water or chlorine stock solutions.     

Determination of halogens via molecules in the air–acetylene flame using high-resolution continuum source absorption spectrometry,Part II: Chlorine

As continuation of the work on fluorine, the second part of the studies of halogens in the air–acetylene flame attends to the determination of chlorine using high-resolution continuum source absorption spectrometry and molecular absorption. In case of chlorine, the diatomic InCl molecule proved to be a suitable species. For an excess of In in the flame, chlorine is converted to InCl which produces a distinctive band head at 267.24 nm that could be evaluated analytically. The influence of concentrated inorganic acids and metallic matrices on the absorption at this band head was tested. In all cases the signal proved to be unaffected, i.e., no spectral interferences were observed. However, serious chemical interferences were found in the presence of sulfuric and phosphoric acids, which could be partially eliminated by adding Ca in the form of nitrate. Moreover, nitric and hydrofluoric acids as well as Cu and Ga matrices also produced significant chemical interferences. Therefore, the method of standard additions should be used for calibration purposes. Concerning the limit of detection, a value of 3 mg L^− 1 was achieved for a measurement time of 5 s in the presence of 10,000 mg L^− 1 In. The calibration curve was linear up to a chlorine concentration of 1800 mg L^− 1. Three certified reference materials (BCR 151, HISS-1, and PACS-2) were analyzed to test the performance of the new method, yielding good precision and accuracy.     

The passivation phenomenon of platinum in fused lithium chloride + potassium chloride eutectic: Part II. Chlorine overpotential and superpassivation of platinum

Platinum is known to have a very high chlorine overpotential, about 0.8 V, in fused lithium chloride + potassium chloride eutectic. The high overpotential can be ascribed to the formation of the thick passivation film of platinum chlorides. The high chlorine overpotential was decreased by the addition of alkali metal oxides and a reversible chlorine evolution was revealed in a similar manner as the graphite electrode. The reversible chlorine evolution was ascribed to the formation of the oxide passivation film. The chlorine overpotential at the oxide film was increased stepwise as the applied potential was made more positive. The stepped transitions of the chlorine overpotential was ascribed to the valence change of the oxide film. Platinum shows a typical N-shaped passivation at +0.65 V versus Ag/AgCl(0.1) which has been ascribed to the dissolution of platinum into Pt(II) ions and following formation of the passivation film of supersaturated Pt(II) chloride. Platinum was found to show another passivation phenomenon at high temperatures, above 450°C. The N-shaped current-potential curve was observed at +1.8 V which was far more positive than the potential of the standard chlorine electrode. The dissolution of platinum prior to the passivation was found to occur due to the formation of high valence platinum ions such as Pt⁶⁺ and Pt⁸⁺.     

Flow-injection potentiometric determination of residual chlorine in water

Residual chlorine is measured in water by using a potentiometric system composed of an iodide-selective electrode and a platinum electrode sensing the iodine-iodide ratio. When the sample is added to acidified iodide solution, the cell response is in a logarithmic relation to the iodine concentration which in turn depends on the concentration of residual chlorine. In the flow injection system evolved, 0.1–5.0 mg l^-1 residual chlorine can be determined at a rate of 40–60 samples per hour. The results of potentiometric determinations of residual chlorine in tap water compared to spectrophotometric results suggest that the presence of various organic substances is responsible for discrepancies between these measurements.     

An automated method for the determination of low-level kjeldahl nitrogen in water and waste water

An entirely automated system for low level Kjeldahl nitrogen determination in water samples is described. Samples are continuously digested at 300 °C with sulfuric acid and hydrogen peroxide to convert the organic nitrogen to ammonia, which is determined colorimetrically with sodium salicylate and sodium dichloroisocyanurate (as chlorine source). The method has a range of 10–500 μg Nl^-1 with good precision and accuracy.     

Charged particle activation analysis of phosphorus in biological materials

Charged particle activation analysis of phosphorus in biological materials using the³¹P (α,n)^34mCl reaction has been studied. Since^34mCl is also produced by the³²S (α,pn) and the³⁵Cl (α, α′ n) reactions, the thick-target yield curves on phosphorus, sulfur and chlorine were determined in order to choose the optimum irradiation conditions. As a result, it was found that the activation analysis for phosphorus without interferences from surfur and chlorine is possible by bombarding with less than 17 MeV alphas. The applicability of this method to biological samples was then examined by irradiating several standard reference materals. It was confirmed that phosphorus can readily be determined at the detection limit of 1 μg free from interferences due to the matrix elements.     

Applications of gamma-spectrometry in determining chlorine in aqueous solutions

A method is described for the radioanalytical determination of traces of chlorine in aqueous solutions without radiochemical separation or purification. Using a gamma-spectrometer with monocrystal scintillator, the sensitivity of the analysis is about 1·10⁻⁸ g of chlorine/ml, the time of analysis being 15 minutes. For the selective determination of chlorine in aqueous solutions containing a large amount of impurities, a bicrystal scintillation sum-coincidence spectrometer was employed with 120×100 mm NaI(Tl) crystals and thus the³⁸Cl cascade radiation could be used. Application of the sum-coincidence spectrometer allowed a reliable determination of 1·10⁻⁷ g of Cl/ml against a background of 1·10⁻⁵ g of Na/ml.     

Differential Pulse Voltammetric Determination of Free Chlorine for Water Disinfection Process

The electrochemical detection of free chlorine based on the reduction at a gold electrode has been studied. The differential pulse voltammetric curves exhibited well‐defined cathodic peaks. Investigations with this system suggested that the active species in the cathodic reaction is HClO. Excellent reproducibility was demonstrated at pH 5. The peak height could be used for accurate and rapid determination of free chlorine in a sample water. A linear relationship (r²=0.99) was found for the concentration range of 1–5 mg Cl dm^?3 and the detection limit was estimated to be 0.04 mg Cl dm^?3.