Determination Of Free Chlorine Research Articles

Enhanced ammonia oxidation by a photoelectrocatalysis‑chlorine system: The role of ClO• and free chlorine

The decomposition of ammonia-N to environmental-friendly N2 remains a fundamental problem for water treatment. We proposed a way to selectively and efficiently oxidize ammonia to N2 through an integrated photoeletrocatalysis‑chlorine reactions (PECCl) system based on a bifunctional TiO2 nanotube photoanode. The ·OH and HClO can be simultaneously generated on the TiO2 nanotube photoanode in this system, which can in situ form ClO· for efficient ammonia removal. Compared with electrochemical‑chlorine (EC-Cl), photocatalysis‑chlorine (PC-Cl) and photoelectrocatalysis (PEC) systems, the PEC-Cl system exhibited much higher electrocatalytic activity due to the synergetic effect of photoelectrocatalyst and electrocatalyst in bifunctional TiO2 nanotube electrode. The removal efficiency of ammonia-N and total-N reached 100.0 % and 93.3 % at 0.3 V (vs Ag/AgCl) in the PEC-Cl system. Moreover, the system was efficient under various pH conditions. The reactions between ClO−/ClO· and the N-containing intermediates contributed to the high performance of the system, which expanded the reactions from the electrode surface to the electrolyte. Furthermore, radical scavenging and free chlorine determination experiments confirmed that ClO· and free chlorine were the main active species that enabled the ammonia oxidation. This study presents new understanding on the role of active species for ammonia removal in wastewater.

Poly(caffeic acid) Redox Couple Decorated on Electrochemically Reduced Graphene Oxide for Electrocatalytic Sensing Free Chlorine in Drinking Water

Regular water quality measurements are essential to the public water supply. Moreover, selective free chlorine (disinfectant) level monitoring without an interfering agent is necessary. The present work aimed to fabricate poly(caffeic acid) (p-CFA) coated on an electrochemically reduced graphene oxide (ERGO) surface for the selective detection of free chlorine. Electron microscopy and various spectroscopic techniques confirmed the p-CFA@ERGO/glassy carbon (GC) electrode. The p-CFA@ERGO/GC coated probe surface coverage was calculated to be 4.75 × 10-11 mol cm-2. The p-CFA@ERGO/GC showed superior catechol/o-quinone oxidation/reduction peaks for electrocatalytic free chlorine determination. The performance of the developed sensor electrode was outstanding, with an extensive range of free chlorine detection (20 μM to 20 mM), high sensitivity (0.0361 µA µM-1), and low detection limit (0.03 µM). The p-CFA@ERGO/GC capability of the realist water samples, such as the tested commercial and tap water, yielded a good range of recovery (from 98.5% to 99.9%). These values align with the standard N,N'-diethyl-p-phenylenediamine reagent method results.

Boron-Doped Diamond as a Quasi-Reference Electrode.

As a working electrode, boron-doped diamond (BDD) has been studied in detail in electrochemical processes because of its superior electrochemical properties. However, these characteristics have rarely been mentioned when BDD is used as a quasi-reference electrode (QRE). Herein, we conducted a systematic investigation on BDD electrodes, with different boron-doping levels (1 and 0.1%) and different surface terminations (hydrogen and oxygen) for their application as a QRE. A BDD electrode with 1% boron and a hydrogen-terminated surface achieved the best stability. Its open-circuit potential (OCP) exhibited less than 100 mV of potential drift over 6000 s and showed a minuscule half-wave potential difference (E1/2) of 0.0037 V in 0.1 mM K3[Fe(CN)6]/1 M KCl solution before and after the OCP measurement. Based on these observations, anions are found to contribute to the potential, which we preliminarily speculate as related to the capacitance caused by electrostatic adsorption on the positively charged hydrogen-terminated surface. The repeatability of measurement was verified through continuous cyclic voltammetry tests in 0.1 mM K3[Fe(CN)6]/1 M KCl, showing a maximum E1/2 difference of 0.042 V. The contribution of the redox couples was excluded, and the repeatability was considered to originate from its surface stability. Finally, a linear response of the optimized BDD as a QRE was validated (R2 > 0.99) by determination of free chlorine and dopamine concentrations, respectively. These results consolidate the existing fundamental research on BDD electrodes and promote the possibility of its application as a QRE in harsh environments or in vivo biological monitoring.

Flow-based green ceramics microdevice with smartphone image colorimetric detection for free chlorine determination in drinking water

The residual free chlorine concentration is an important parameter to evaluate the potability of water and the efficiency of disinfection in the water treatment system. As a restricted range of residual free chlorine concentration at all points of the distribution network is needed to ensure efficiency and to avoid deleterious effects, fast and in situ quantification of this specie is important. This work deals with the development and validation of two procedures based on DPD (N,N-diethyl-p-phenylenediamine) and OT (ortho-tolidine, 3,3-dimethylbenzidine) for the determination of residual free chlorine in water by exploiting a flow-based microdevice built with Low Temperature Co-Fired Ceramic (LTCC) technology. The analytical signal was monitored by a smartphone camera through RGB values obtained by a free application (Color Grab®). Under optimized conditions, linear ranges within 0.6–2.5 mg/L and 0.1–2.3 mg/L were obtained for DPD and OT methods, with limits of detection and quantification of 0.023 and 0.077 mg/L (DPD) and 0.026 and 0.089 mg/L (OT). Precision expressed as RSD (2.0 mg/L free chlorine, n = 10), was 1.3 % and 0.7 %, respectively. Both procedures were successfully applied to the analysis of samples from a water treatment plant. The flow-based microdevice coupled to digital-image colorimetry is an innovative, sustainable, and cost-effective analytical tool for in-field chemical analysis.

A novel cyclic voltammetric determination of free chlorine generated by ozone disinfection in seawater aquariums

The amount of free chlorine generated by disinfection is one of core parameters that should be monitored for the seawater aquarium. This article proposes a novel analytical method in which the amount of free chlorine in ozonized seawater can be determined by the conventional cyclic voltammetry (CV) with a bare platinum disk electrode without developing any new sensing material. The amounts of both free chlorine and ozone in ozonized seawater samples were determined by spectrophotometry, which showed that most of ozone was converted to free chlorine. CV experiments with a bare platinum electrode were carried out for the samples and our attention was paid to that the peak current of hydrogen oxidation generated by water electrolysis, which was ignored in the previous studies, depends on the amount of free chlorine in the sample. The CVs exhibited the well–defined oxidation peak for hydrogen molecules and the linear range of free chlorine amounts in the ozonized seawater samples spanned from 0.02 to 0.4 mg L–1 with a correlation coefficient of 0.9982 (n=5), a detection limit of 1.2 × 10–2 mg L–1 at 3σ and a high sensitivity of 4063 μA cm–2 mg–1 L. The repeatability of this technique had a relative standard deviation of 4.41% (n=10).

Free Chlorine Determination in Disinfectant Product using Visible Spectrophotometry based on Prussian Blue Degradation

Disinfectant products with excessive chlorine could be dangerous for health and need quality control. It is important to develop an analytical method for monitoring product quality. The main objective of this work is to develop an alternative method and evaluate the analytical performance of visible spectrophotometry for determining free chlorine in disinfectant products based on the Prussian blue decomposition process. The capability of chlorine to oxidize ferrous to ferric ions makes the Prussian blue generated by ferrosulfate and potassium ferricyanide is decomposed and measured by spectrophotometer. The formation of Prussian blue was improved by optimizing some reaction conditions and assessing incubation time. Linearity, analytical concentration range, precision, accuracy, detection limit, and quantitation limit parameters were among the examined analytical parameters. The results showed that the optimum concentration of ferrosulfate, potassium ferysianide, and hydrochloric acid for Prussian blue formation was 2.0 mmol L-1, 3.0 mmol L-1, and 0.5 mol L-1, respectively, with 15 minutes incubation time after chlorine addition. Analytical performance parameters seemed appropriate for routine analysis purposes. The developed method can also be applied as an alternative analytical method to determine the free chlorine concentration of disinfection products in the market.

Simple-to-use and portable device for free chlorine determination based on microwave-assisted synthesized carbon dots and smartphone images

A new portable and simple 3D printed device was designed for free chlorine determination in water samples. The analytical method was based on the quenching caused by free chlorine on the fluorescence emission of the carbon dots (CD) synthesized from citric acid and urea. The fluorescence was captured through the camera of a smartphone, which was coupled to the 3D printed device, and the images were processed using the RGB system by the ImageJ 1.51q software. The proposed method was selective and precise (RSD% 4.6, for n = 6), and the trueness of the results was evaluated by comparing the results obtained with those recovered by the spectrophotometric method 4500-Cl G (standard method), with good agreement between them. Moreover, the remarkable correlation between the CD signal and the free chlorine concentration resulted in a determination with low detection limits (limit of detection of 6 μg L−1 and limit of quantification of 20 μg L−1). Therefore, the new method and the related portable device could be considered a fast, economical and reliable alternative for the on-site determination of free chlorine in water samples.

Determination of free chlorine based on ion chromatography\u2014application of glycine as a selective scavenger

Free available chlorine (FAC) is the most widely used chemical for disinfection and in secondary disinfection; a minimum chlorine residual must be present in the distribution system. FAC can also be formed as an impurity in ClO2 production as well as a secondary oxidant in the ClO2 application, which has to be monitored. In this study, a new method is developed based on the reaction of FAC with glycine in which the amine group selectively scavenges FAC and the N-chloroglycine formed can be measured by ion chromatography with conductivity detector (IC-CD). Utilizing IC for N-chloroglycine measurement allows this method to be incorporated into routine monitoring of drinking water anions. For improving the sensitivity, IC was coupled with post-column reaction and UV detection (IC-PCR-UV), which was based on iodide oxidation by N-chloroglycine resulting in triiodide. The method performance was quantified by comparison of the results with the N,N-diethyl-p-phenylenediamine (DPD) method due to the unavailability of an N-chloroglycine standard. The N-chloroglycine method showed limits of quantification (LOQ) of 24 μg L−1 Cl2 and 13 μg L−1 Cl2 for IC-CD and IC-PCR-UV, respectively. These values were lower than those of DPD achieved in this research and in ultrapure water. Measurement of FAC in the drinking water matrix showed comparable robustness and sensitivity with statistically equivalent concentration that translated to recoveries of 102% for IC-CD and 105% for IC-PCR-UV. Repeatability and reproducibility performance were enhanced in the order of DPD, IC-CD, and IC-PCR-UV. Measurement of intrinsic FAC in the ClO2 application revealed that the N-chloroglycine method performed considerably better in such a system where different oxidant species (ClO2, FAC, chlorite, etc.) were present.

Field analysis free chlorine in water samples by a smartphone-based colorimetric device with improved sensitivity and accuracy

It is highly desirable to regularly monitor the concentration of free chlorine in water samples because residual free chlorine can greatly affect the health of human and the growth of aquatic baby animals. Visual colorimetry is a cost-effective method to monitor the concentration of residue chlorine in water. To reduce the errors from estimating the hue by naked eyes and to enhance the sensitivity, we propose a smartphone-based portable colorimetric device with long-path and self-calibration ability. The key idea relies on a flow colorimetric tube with the illumination in empty tube or at a low absorption wavelength as the internal references to correct the baseline drift due to light source intensity decay. The self-focusing ability in the round-bottom colorimetric tube is helpful to simplify the design of the portable device. The absorbance measured by proposed device obeyes the Lambert-Beer law in the range of 0–1. By using N,N‑diethyl‑p‑phenylenediamine as the colorimetric regent, the proposed method demonstrates a promising result for the determination of free chlorine with the linear range of 0.8–14 μM and the limit of detection of 0.23 μM. This simple colorimetric device offers the advantages of cost effectiveness, ease of implementation, portability, sensitivity and reliability for field analysis.

Study on microfluidic paper-based analytical device layouts for simultaneous analysis purposes applying colorimetric reactions

In this project, the adequacy of different layouts for Paper-based Analytical Device (μPAD) for simultaneous analysis in mixtures was evaluated through the use of colorimetric reactions in their reactional zones. Hence, the following parameters of the μPAD were varied: width of the hydrophobic barrier, width and length of the hydrophylic channel, shape and dimensions of the reactional zones, and geometry of the device. The analytical system used in this research was based in comercial tests for domestic quality control of pool water with pH measure through Phenol Red deprotonation, and free chlorine determination through o-Toluidine oxidation.

On site determination of free chlorine in water samples by a smartphone-based colorimetric device with improved sensitivity and reliability

Absorbance in a long-path portable colorimetric device was measured by a ratiometric fluorescent strategy in a smartphone platform.

Highly sensitive solution-gated graphene transistor based sensor for continuous and real-time detection of free chlorine

The concentration of free chlorine used for sterilizing drinking water, recreational water, and food processing water is critical for monitoring potential environmental and human health risks, and should be strictly controlled. Here, we report a highly efficient solution-gated graphene transistor (SGGT) device, for the detection of free chlorine in a real-time and convenient manner with excellent selectivity and high sensitivity. The detection mechanism of the SGGT with Au gate electrode is attributed to two combined effects: the reduction of the free chlorine on Au gate electrode; and the direct oxidization of graphene by the free chlorine in solution. The SGGT device shows a linear response range of free chlorine from 1 μM to 100 μM, with detection limit as low as 100 nM, far beyond the sensitivity required for practical applications. Finally, we also demonstrate the performance of the SGGT for determination of free chlorine in local tap water samples. The results presented herein have important implications in the development of portable and disposable devices based on SGGT sensing platform for the simple, real-time, and selective determination of free chlorine.

A LED-based fiber-optic sensor integrated with lab-on-valve manifold for colorimetric determination of free chlorine in water

In this work, a colorimetric methodology was developed for free chlorine determination by constructing a fiber-optic sensor (FOS) which was designed by using a small LED as light source and two silica fibers as light transmission elements. Then the FOS was integrated with the sequential injection lab-on-valve (SI-LOV) manifold to fabricate a FOS-SI-LOV system for free chlorine detection. The colorimetric determination was based on the reaction between N,N-diethyl-p-phenylenediamine (DPD) reagent and free chlorine, which would produce a chromophore showing maximum absorbance at 511 and 551nm and detected by a micro spectrometer detector. By choosing a green LED with emission wavelength at 520nm as light source, the chlorine concentration could be simply evaluated according to Beer's law. The developed FOS-SI-LOV system showed improved performances of wide linear range (10–400μgL−1), low detection limit (3.5μgL−1, 3σ), fast analysis (6.85s) and excellent repeatability (0.0083 RSD, n=8) for chlorine determination. The proposed FOS-SI-LOV system has been applied to on-line and real-time chlorine determination in different water samples with excellent selectivity. Furthermore, this FOS-SI-LOV methodology provided a colorimetric and fluorescence detection platform for other hazardous species monitoring in water environment based on Beer's law and Stern-Volmer relationship, respectively.

A miniaturized evanescent-wave free chlorine sensor based on colorimetric determination by integrating on optical fiber surface

Chlorine is a powerful oxidizing agent extensively used in water disinfection and blanching processes. Too low or too high chlorine concentration in water supplies would cause hazards for water usage. In this work, a miniaturized microfluidic evanescent-wave sensor was developed for colorimetric determination of free chlorine in water. A microfluidic channel with narrow dc (50μm) was constructed to act as both flow cell and detection cell in this sensor. When light propagated by total internal reflection (TIR) in the fiber core, evanescent wave produced on the fiber surface could interact with the DPD reagents and produce absorption change. The free chlorine could be determinated by colorimetric method and evaluated by absobance according to Beer’s law. This miniaturized sensor showed improved performances of small detection volume (1.2μL), fast analysis (4.42s), low detection limit (1.5ppb) and excellent repeatability (1.59%) for chlorine determination. The sensor was applied to chlorine determination in different water samples. The results obtained were compared with those obtained by conventional spectrophotometry and iodometry, showing agreement and validating the sensor’s potential applications. Meanwhile, the fabrication of this sensor provides a miniaturized and portable detection platform for other hazardous species monitoring by simple modular design.

Electrocatalytic Reduction of Free Chlorine at an N,N-Diethylaniline-grafted Carbon Electrode for Improved Sensitivity in Amperometric Detection.

The electrocatalytic activity of an N,N-diethylaniline-grafted carbon (DEA/PFC) electrode was utilized to improve the sensitivity in the cathodic detection of free chlorine. Voltammetric curves showed a well-defined cathodic peak of free chlorine on DEA/PFC, lowering the overlap with that of dissolved oxygen. Amperometric measurements were applied for the determination of free chlorine for a concentration range of 4 orders of magnitude. The results showed that measurements of the amperometric response with DEA/PFC can be used as the basis for a simple, accurate, and rapid method to determine free chlorine.

Manganese dioxide nanosheets as an optical probe for photometric determination of free chlorine

We report on a colorimetric assay for free chlorine using MnO2 nanosheets as an optical probe. In the absence of free chlorine, the addition of ascorbic acid (AA) causes the chemical dissolution of MnO2 nanosheets via a redox reaction to result in low absorbance. However, if a solution containing free chlorine is added to the system, AA will be oxidized by free chlorine and the MnO2 nanosheets will not longer be dissolved. Hence, the AA-induced decoloration will not take place and solution will remain yellow. Under optimized experimental conditions, there is a linear relationship between the change in absorbance at 370 nm and the concentration of free chlorine in the 0.2 to 10 μM concentration range, with an 80 nM detection limit. The detection limit for visual evaluation is 8.0 μM. The assay is fairly selective for free chlorine over common inorganic ions and small organic substances. It was applied to the determination of free chlorine in tap water using the standard addition method.

Amino-Functionalized Metal-Organic Frameworks Nanoplates-Based Energy Transfer Probe for Highly Selective Fluorescence Detection of Free Chlorine.

Novel highly fluorescent NH2-MIL-53(Al) was controllably synthesized by a facile one-step hydrothermal treatment of AlCl3·6H2O and NH2-H2BDC in water with urea as a modulator. The as-synthesized NH2-MIL-53(Al) nanoplates exhibited excellent water solubility and stability. In the present work, it can be found that strong fluorescence of NH2-MIL-53(Al) nanoplates was significantly suppressed after the addition of free chlorine, and a simple sensing system for fast, highly selective direct detection of free chlorine in water was established. Compared with other fluorescent sensors for free chlorine, the present methodology has a comparable detection limit of 0.04 μM (S/N = 3) and a wide detection range of 0.05 to 15 μM. On the other hand, the traditional redox-based fluorescent probes sharply suffered from the interference of MnO4(-), Cr2O7(2-), and other oxidants with stronger oxidation capability than free chlorine while ours overcame this disadvantage. Further research suggests that it is more likely the energy transfer through N-H···O-Cl hydrogen bonding interaction between amino group and ClO(-) ions plays the key role in our system, providing a new and promising platform for free chlorine determination in water quality monitoring.

Chemiluminescence reaction of glucose-derived graphene quantum dots with hypochlorite, and its application to the determination of free chlorine

Graphene quantum dots (GQDs) were prepared by a new and facile procedure, and their chemiluminescence (CL) reaction with hypochlorite was studied. It was found that hypochlorite can directly oxidize GQDs to give rise to CL emission, and that the surfactant cetyl trimethyl ammonium bromide enhances CL by a factor of about 18. CL and fluorescence spectra were acquired, and the effect of radical scavengers on the reaction was studied. This CL system was used to develop a simple and sensitive method for the determination of hypochlorite in the 0.5 μM to 1.0 mM concentration range, with a detection limit of 0.3 μM. The method was successfully applied to the determination of free chlorine in (spiked) samples of tap water and pool water.

잔류염소 측정용 전기화학센서의 유효성

AbstractSodium hypochlorite is used worldwide as a water disinfectant and in bleaching agent. Sodium hypochlorite applied to water initially undergoes hydrolysis to form free chlorine consisting of hypochlorous acid(HOCl) and hypochlorite ion(OCl - ). For free chlorine determination, an electrochemical method is simple due to the electroactivity of free chlorine; it measures current and is free of most reagents. Amperometric free chlorine sensor has been developed with gold (Au)-based electrode. The 3-electrode free chlorine sensor whose working and counter electrodes were Pt exhibited excellent response to HClO at +400mV vs. Ag/AgCl/sat. KCl. In addition, the use of a pH error correction algorithm provided a reliable measurement of residual free chlorine in water sample without any pretreatment in the normal pH range(pH 6~8) of municipal water supply. The free chlorine sensor installed in on-line monitoring system could be used to continually monitor the level of residual free chlorine in real samples.

Rapid and selective determination of free chlorine in aqueous solution using electrophilic addition to styrene by gas chromatography/mass spectrometry

We developed a rapid and selective method for determination of free chlorine in aqueous solution by gas chromatography/mass spectrometry for the first time. Free chlorine was converted to styrene chlorohydrin using electrophilic addition to styrene in sodium acetate buffer solution (pH 5). The chlorine derivative obtained was extracted with chloroform, and then analyzed by GC/MS. The calibration curve showed good linearity from 0.2–100μg/mL (as available chlorine). The detection limit was 0.1μg/mL, and the intra- and interday accuracy were measured at concentrations of 10, 50, and 75μg/mL to be −1.3 to 6.9% (intraday) and 3.8–8.0% (interday) as % Bias. The precision was between 1.4 and 4.5% as % RSD. These results indicate that this method is a superior technique for the identification of free chlorine. This method was successfully applied to quantification in commercial samples and in samples of a criminal case.