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An improved N,N′-diethyl-p-phenylenediamine (DPD) method for the determination of free chlorine based on multiple wavelength detection
Abstract
The N,N′-diethyl-p-phenylenediamine (DPD) standard method for the determination of free chlorine by spectroscopic detection at 515 nm has a limited analytical range, 0.7–56 μmol l−1. It is shown that detection performed at 324 nm enhances the method sensitivity by a factor of 2. For analyte concentrations above 100 μmol l−1, a decrease in the absorbance is observed at 515 nm, making the method ambiguous, while the absorbance still increases at 324 nm. By applying partial least squares (PLS) regression based on multiple absorbance values in the interval 200–600 nm, the useful analytical range can be extended further, up to 200 μmol l−1. This improvement is achieved whilst maintaining root mean square errors of cross-validation (RMSECV) of the same order as for the univariate standard method. The multivariate approach also enables identification of samples containing interfering metals, here as Fe3+, which form light absorbing chelates with EDTA.
... Consequently, it plays a Organics 2024, 5 615 significant role in forensic toxicology. Several analytical techniques have been reported for the determination of free chlorine, and numerous approaches have been established for that purpose, including iodometric titration [7], ion chromatography [8,9], colorimetry [10][11][12][13], chemiluminescence [14,15], liquid chromatography [16,17], flow injection analysis [5], and gas chromatography-mass spectrometry [17][18][19]. Most recently, dual-mode determination (colorimetric and fluorometric) of hypochlorite has been developed [20]. ...
... A stock solution of free chlorine was prepared by diluting an aqueous sodium hypochlorite ion mixture with water to a concentration of 1 mg/mL. This stock solution was standardized via the iodometric method [11] and was diluted to various concentrations with water. Each standard (blank, 0.1 µg/mL, 1 µg/mL, 5 µg/mL and 10 µg/mL) was prepared in triplicate. ...
We developed a selective technique to rapidly measure free chlorine, which is the sum of elemental chlorine (Cl2), hypochlorous acid (HOCl), and hypochlorite (OCl−) in water samples via an electrophilic aromatic substitution reaction hyphenated with liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Sample preparation involved derivatization at 25 °C for 15 min with 3,4,5-trimethoxyphenylacetic acid (TMPAA) in an aqueous solution prior to analysis. Several parameters were evaluated to determine the optimized reaction and for the production of informative MS/MS spectrum of the derivatization product, 2-chloro-3,4,5-trimethoxyphenylacetic acid (Cl-TMPAA). The resulting Cl-TMPAA derivative displayed an informative ESI-MS/MS spectrum characterized by product ions at m/z 232.0142, 200.0245, and 185.0009 from the precursor ion at m/z 259.0379. The linear dynamic range of the method (0.1–10 µg/mL) was fitted to concentration levels relevant to forensic toxicology issues. Compared with other analytical techniques, this newly established LC-MS-based method demonstrated specificity, simplicity, and rapidity. This method enables the detection of free chlorine for forensic investigations in criminal cases.
... [18][19][20] The current standard for measuring free chlorine is a colorimetric method which requires the use of N,N′-diethyl-pphenylenediamine (DPD), but this method is toxic, prone to error, expensive, and not user-friendly. [8,[21][22][23] The above-described approaches to measuring free chlorine levels in water have several limitations including being time consuming or involving expensive laboratory-based equipment. [24] As a result, alternative sensing technologies must be used to address these limitations. ...
... Due to the difficulty associated with the use of these ion buffers, its use did not become as wide-spread as colorimetric methods such as DPD or other electrochemical methods. [23] A standard potentiometric sensor is made of two electrodes: the working electrode made of the analyte-sensitive material, and a reference electrode commonly made with Ag/AgCl (Figure 9). When both electrodes are submerged in the solution, the open circuit potential between them provides the ClO − concentration in the solution. ...
Sodium hypochlorite is a widely used additive in water used to disinfect and remove any disease‐causing bacteria that can be found in sources of water, and is used to wash contaminants from meats, fruits, and vegetables. Many free chlorine sensors exist which monitor free chlorine levels such as the use of colorimetric or electrochemical methods, ensuring that the free chlorine is within safe and regulated levels. However colorimetric sensing methods are irreversible and often use toxic compounds, and electrochemical sensors, although reversible, are made with materials which are not suitable to be used near drinking water or food products. By developing sensors which are made using alternative materials and methods, the sensors can be used in and around drinking water and food products. This review article discusses various electrochemical‐free chlorine sensors made with various carbon‐based materials and methods resulting in sensors that are biodegradable, relatively inert, and resilient in the presence of harsh chemicals, making them safe to use near and around food and still maintain competitive performance parameters. This review article showcases some of the recent progress, the importance, preconditions, and the various future needs and potentials of carbon‐based electrochemical‐free chlorine sensors.
... To identify the compounds, many measurement methods have been developed and used to date. Absorption photometry, iodometric titration (KI), the N,N-diethyl-p-phenylenediamine sulfate (DPD) method, and electron spin resonance (ESR) are usually used to identify and quantify chlorine compounds contained in chlorous acid solution [14,15]. The results obtained are also used as indicators of bactericidal activity [11]. ...
... The results obtained are also used as indicators of bactericidal activity [11]. Total chlorine can be calculated by the KI method, and free available chlorine (FAC) can be calculated by the DPD method [15,16]. However, it is not clear what species in the sodium chlorite solution possess disinfecting action. ...
With the spread of coronavirus infections, the demand for disinfectants, such as a sodium chlorite solution, has increased worldwide. Sodium chlorite solution is a food additive and is used in a wide range of applications. There is evidence that chlorous acid or sodium chlorite is effective against various bacteria, but the actual mechanism is not well understood. One reason for this is that the composition of chlorine-based compounds contained in sodium chlorite solutions has not been clearly elucidated. The composition can vary greatly with pH. In addition, the conventional iodometric titration method, the N,N-diethyl-p-phenylenediamine sulfate (DPD) method and the absorption photometric method cannot clarify the composition. In this study, we attempted to elucidate the composition of a sodium chlorite solution using absorption spectrophotometry and ion chromatography (IC). IC is excellent for qualitative and quantitative analysis of trace ions. Through this, we aimed to develop an evaluation method that allows anyone to easily determine the bactericidal power of sodium chlorite. We found that commercially available sodium chlorite solution is 80% pure, with the remaining 20% potentially containing sodium hypochlorite solution. In addition, when sodium chlorite solution became acidified, its absorption spectrum exhibited a peak at 365 nm. Sodium chlorite solution is normally alkaline, and it cannot be measured by the DPD method, which is only applicable under acidic conditions. The presence of a peak at 365 nm indicates that the acidic sodium chlorite solution contains species with oxidizing power. On the other hand, the IC analysis showed a gradual decrease in chlorite ions in the acidic sodium chlorite solution. These results indicate that chlorite ions may not react with this DPD reagent, and other oxidizing species may be present in the acidic sodium chlorite solution. In summary, when a sodium chlorite solution becomes acidic, chlorine-based oxidizing species produce an absorption peak at 365 nm. Sodium hypochlorite and sodium chlorite solutions have completely different IC peak profiles. Although there are still many problems to be solved, we believe that the use of IC will facilitate the elucidation of the composition of sodium chlorite solution and its sterilization mechanism.
... TDS, electrical conductivity and water temperature were also measured on the spot using a Test Assured three-in-one portable meter. Residual chlorine was measured using ready-to-use kits that use the DPD Method (N,N-Diethylphenylenediamine) [31] by dissolving the DPD from the powder pillow in 10 mL of the sample and then comparing the developed color with standard charts available with the kit. Fluoride was measured by the Zirconium Xylenol Orange (BARC Technology, Mumbai, India), a colorimetric method [32]. ...
... conductivity and water temperature were also measured on the spot using a Test Assured three-in-one portable meter. Residual chlorine was measured using ready-to-use kits that use the DPD Method (N,N-Diethylphenylenediamine) [31] by dissolving the DPD from the powder pillow in 10 mL of the sample and then comparing the developed color with standard charts available with the kit. Fluoride was measured by the Zirconium Xylenol Orange (BARC Technology, Mumbai, India), a colorimetric method [32]. ...
A semester-long internship was designed for undergraduate students at the University of Delhi, India. Teams comprising 30 students from all over the University were trained to carry out field exploration activities on the Yamuna River flowing in Delhi. The students were provided with portable kits to measure the physicochemical parameters at a selected bank of the Yamuna River. Students documented the invertebrate fauna in the riparian zone of the banks. At the same time, they noted the anthropogenic polluting activities on the bank of the Yamuna River. This internship educated students about the UN’s Sustainable Development Goals (SDGs). They all studied Ecology and Environmental Science in their undergraduate curriculum, but they all confessed that they were unaware of the 17 SDGs and the deteriorating health of the Yamuna River in the city. We educated students about the freshwater emergency recovery plan and the International Union for Conservation of Nature (IUCN) red list of ecosystems. This internship is a great example of an undergraduate-directed study or research experience that supported student constructivism and inquiry-based learning, and this research article elaborates on student reports and situational interest in freshwater biology to achieve SDG6.
... The formation of CER products from chloride oxidation was quantified using the established diethylphenylenediamine (DPD) method to investigate CER suppression of the oxyhydroxides during electrolysis of the neutral pH saline electrolyte. 36 As such, CA testing was also performed in the neutral saline electrolyte to investigate the stability of the codoped oxyhydroxides under a relatively high potential of 1.7 V (vs reversible hydrogen electrode (RHE)) inducive of higher chloride corrosion. Selectivity measurements through online FE calculations showed high OER selectivity in alkaline (FE ∼ 97%) and neutral (FE ∼ 91%) pH saline conditions under standard 10 mA cm −2 operation. ...
... For quantification of CER species (HClO and ClO − ), the N,N-diethyl-p-phenylenediamine (DPD) method using the Hack kit was used. 36 Electrolyte samples were collected after 6 h of chronoamperometry (CA) testing conducted at pH 7 using the phosphate-buffered saline electrolyte at 1.7 V (vs RHE) and analyzed for CER species. Faradaic efficiency (FE) calculations for OER selectivity were performed through gas chromatography (GC) measurements of oxygen evolution at known time intervals during chronoamperometric testing in a gas-tight three-electrode cell. ...
Green hydrogen presents itself as a clean energy vector, which can be produced by electrolysis of water by utilizing renewable energy such as solar or wind. While current technologies are sufficient to support commercial deployment of fresh water electrolyzers, there remain a few well-defined challenges in the path of commercializing direct seawater electrolyzers, predominantly related to the sluggish oxygen evolution reaction (OER) kinetics and the competing chlorine evolution reaction (CER) at the anode. Herein, we report the facile and swift fabrication of an S,B-codoped CoFe oxyhydroxide via solution combustion synthesis for the OER with apparent CER suppression abilities. The as-prepared S,B-(CoFe)OOH-H attained ultralow overpotentials of 161 and 278 mV for achieving current densities of 10 and 1000 mA cm–2, respectively, in an alkaline saline (1 M KOH + 0.5 M NaCl) electrolyte, with a low Tafel slope of 46.7 mV dec–1. Chronoamperometry testing of the codoped bimetallic oxyhydroxides showed very stable behavior in harsh alkaline saline and in neutral pH saline environments. S,B-(CoFe)OOH-H oxyhydroxide showed a notable decrease in CER production in comparison to the other S,B-codoped counterparts. Selectivity measurements through online FE calculations showed high OER selectivity in alkaline (FE ∼ 97%) and neutral (FE ∼ 91%) pH saline conditions under standard 10 mA cm–2 operation. Moreover, systematic testing in electrolytes at pH values of 14 to 7 yielded promising results, thus bringing direct seawater electrolysis at near-neutral pH conditions closer to realization.
... The generation of ROS (•OH) and RCS (•Cl and •ClO) was detected via electron spin resonance (ESR) spectrometer (Bruker A300, Bruker, German) using the 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as the radical spin-trapped agent. The N, N-diethyl-p-phenylenediamine (DPD) standard method was used to verify the stability of the system [29,30]. The details are provided in the Supporting information. ...
... Based on the above ESR results and related literatures [22,23,38], a possible photocatalytic chlorine activation mechanism in the 0.5% Neu-NaClO/TiO 2-x + VL system was illustrated in Fig. 3b The stability of the system was evaluated in a N, N-diethyl-p-phenylenediamine (DPD) assay ( Fig. 3c and 3d) [29,30]. In general, the stability of the solutions followed the sequence: 0.5%Alk-NaClO + VL > 0.5%Neu-NaClO + VL > 0.5%Neu-NaClO/TiO 2-x + VL. ...
Root canal irrigation is an essential step for ensuring successful root canal therapy (RCT). Among available irrigants, sodium hypochlorite (NaClO) (0.5%-5.25%) is the most used irrigant solution because of its comprehensive ability to kill bacteria and dissolve organic tissues. Hence, high concentration of NaClO may have negative effects that would lead to devastating complications, and low concentration of NaOCl is safe but shows decreased efficacy. Therefore, a safe and efficient novel catalysis-enhanced root canal irrigant system consisting of 0.5% neutral-NaClO (pH=7.5), TiO2-x nanoparticles (5 mg mL⁻¹), and visible light irradiation (LED, 10 W, 405-800 nm) was proposed. The effect of the photocatalytic chlorine activation rapidly increased the generation of reactive oxygen species (ROS, •OH) and reactive chlorine species (RCS, •Cl and •ClO) in the system. Consequently, the system exhibited greatly enhanced degradation ability toward methylene blue and typical biological macromolecules, implying its good antibacterial and tissue dissolution activities. Additionally, the antibacterial rates against Enterococcus faecalis in both planktonic and biofilm forms were >99% after treatment with the proposed system for 5 min, which was comparable to that of the 3% alkaline NaClO. Meanwhile, the system showed desirable pulp tissue-dissolving efficacy, successfully solving the dilemma caused by neutralization. L929 cell experiments as well as rats subcutaneous injection experiments demonstrated the biocompatibility and safety of the system. This work describes a safe and effective endodontic irrigant and proposes a promising strategy for developing NaClO-based disinfectants for wider application.
... [21] DPD •+ radical is stabilized by resonance and acquires a fairly stable magenta color with an absorbance wavelength of 551 nm, which is quantitively proportional to the concentration of the TRC in the sample. [22] The DPD colorimetric method provides a fast response and high consistency under various conditions, making it the most commonly applied TRC measurement method in BWMS. However, there are several shortcomings associated with the DPD method such as generating waste stream due to usage of the toxic chemical reagent and requiring periodic replacement of the reagent. ...
Ballast water, which is seawater taken onboard ships to ensure stable and maneuverable sailing, can pose a significant threat to marine ecosystems and human health when discharged owing to the presence of undesirable organisms. To mitigate this risk, ballast water treatment methods such as electrochlorination are employed, where oxidants such as hypochlorite are generated to effectively eliminate marine microorganisms. The effectiveness of an electrochlorination‐based ballast water management system (BWMS) depends on the maintenance of optimal concentrations of total residual chlorine (TRC). However, excessive levels of free chlorine (Cl) can result in corrosion and environmental damage, rendering the accurate monitoring of TRC levels crucial for the safe discharge of ballast water. This review focuses on recent advancements in electrochemical sensors for free Cl measurement in BWMS. The process of free Cl generation, techniques for electrochemical detection, and factors influencing sensor performance are elucidated. In addition, materials and strategies for improving the performance of the sensors are described. Finally, perspectives on the current issues and future challenges that must be overcome to effectively utilize electrochemical detection in BWMS are discussed, thereby offering new directions for advancing this technology.
... 38 By adding catalytic amounts of potassium iodide (KI) accompanied by a second absorbance reading, the DPD method can determine the total chlorine in the sample (both free and combined). 39 This method has been integrated with both colour wheel test kits and digital colorimeters for free chlorine detection. Colour wheel test kits utilize a tablet or powder form of DPD, which will turn the water sample pink if chlorine is present. ...
Clean and safe water is a vital resource for human life. To ensure that consumable water is bacteria-free, water treatment, including the widely used chlorination process, is performed. Free chlorine resulting from the chlorination process in consumable water is a dangerous analyte and it is one of the vital parameters in water quality monitoring. Global guidelines state that free chlorine in consumable water should be controlled at 0.2–5.0 mg L; deviations from this concentration range could cause consumers to suffer from dire health effects. To control the concentration within the said range, various methods for free chlorine monitoring have been developed in recent years, categorized into conventional, optical and electrochemical methods. However, limitations such as high cost and complexity of analysis prevent these conventional methods from meeting the “Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free and Deliverable to end users” criteria for diagnostic tests set by the World Health Organization. Paper-based methods are therefore introduced to replace the conventional methods in the hope of meeting the criteria. However, the paper-based methods are still confined to the lab scale and are highly dependent on chemicals for the detection of free chlorine. Therefore, the capabilities of carbon quantum dots are introduced as a suitable indicator for free chlorine measurement. Using carbon quantum dots as an indicator is recommended for the future development of sustainable portable paper-based sensors due to their excellent absorption and fluorescent properties; in addition, carbon quantum dots can be synthesized from natural resources.
... Furthermore, colorimetric methods are known to suffer from limitations such as being consumable or non-reusable, and the compounds that are required to cause the chemical change are toxic. [44,45] The compound used for this system is o-Toluidine, a known carcinogen, which is known to cause urinary-bladder cancer in people. [46,47] Although the accuracy of the system is excellent, the toxic effect of the compound makes it undesirable to use near drinking water, food, and food products, which require the use of safer non-toxic alternatives. ...
Electrochemical sensors are used to measure target analytes in water, meat, fruits, or vegetables, to ensure their safety, security, and integrity for human use. In this paper, a solution‐based fabrication process is presented for a biodegradable electrochemical free chlorine sensor using asparagine that is functionalized onto graphene oxide (GO). An ink solution of the GO functionalized with asparagine is synthesized, and then deposited onto a screen‐printed carbon electrode (SPCE) using a spin coater. The sensor shows high a sensitivity of 0.30 µA ppm⁻¹ over a linear range of 0–8 ppm with a hysteresis‐limited resolution of 0.2 ppm after achieving a steady state at 50 s. From the development and testing of the free chlorine sensor, over 9000 datapoints are collected and used for training an artificial neural network (ANN) model to quantify and characterize the factors affecting the free chlorine sensor's performance, and model its degradation characteristics. The model reports a low mean absolute error (MAE) of 0.1603 and a high model accuracy with a Pearson correlation coefficient (PCC) of 0.9950, demonstrating that these degradation characteristics can be modeled and be used to compensate the degraded performance characteristics of the free chlorine sensors.
... Finally, the pipetting arm withdraws a small amount of the electrolyte from the cell, mixes it with a coloring reagent, and measures the solution absorption using a plate reader to quantitate the generated HClO (Fig. 2e). 21 Aer each measurement, the solution is automatically replenished from the tank behind the robot. More detailed experimental procedures and video recordings of each step are provided in the ESI. ...
The expected shift from fossil fuels to H2 as the main renewable energy carrier inspires the search for inexpensive, reliable, and green H2 production methods such as seawater electrolysis. However, the noble metal-based catalysts used for electrolytic H2 production are costly and should be replaced by cheaper non-noble metal–based ones. Currently, progress in this field remains slow because of the multidimensionality and vastness of the related search space. Herein, a high-throughput automatic robot was used to prepare Co–Mn–Fe–Ni–based composite-oxide anodic electrocatalysts and characterize their ability to promote the selective and stable production of O2/HClO at the anode during the electrolysis of model seawater (aqueous NaCl). Moreover, machine learning–aided composition optimization was performed using a Bayesian optimization framework. The adopted approach is not limited to electrocatalysts and thus accelerates research and development in the field of materials chemistry and paves the way for technological advances.
... The total concentrations of heavy metal cations and As in solutions were measured using a Varina AA240FS atomic absorption spectrometer and Haiguang AFS-8530 atomic fluorescence spectrometer, respectively. Dissolved total chlorine and Fe(II) were spectrophotometrically detected with the N,N-diethyl-p-phenylenediamine (DPD) (Moberg and Karlberg, 2000) and phenanthroline method (Tamura et al., 1974), respectively. Citrate concentration in the leachate was quantitatively analyzed by the high performance liquid chromatography (HPLC) method. ...
Heavy metal pollution of soils has become a serious environmental problem. Soil washing with degradable reagents is an effective remediation technique of heavy metal pollution, and the generated leachate must be appropriately treated before discharge. However, the existing methods usually have the problems of large consumption of regents, high cost, and secondary pollution. This study proposed a reagent-free electrochemical precipitation method to remove mixed heavy metal ions extracted from soils by citrate using inert electrodes (IrO2-Ta2O5/Ti anode and graphite cathode). The results showed that the low potential of cathode led to the electrodeposition of Cd; the local alkaline environment provided by electro-mediated water reduction caused the hydrolytic precipitation of Zn and Pb; and the precipitation of Fe washed out from Fe-rich soil resulted in the coprecipitation of As on cathode surface. These combined cathodic precipitation processes decreased the concentrations of toxic heavy metals by over 99.4% after 12 h of electrolysis at 26 mA cm-2. The electrodes exhibited high stability after multiple successive cycles of reuse. The concentrations of As, Zn, Pb and Cd in the leachate decreased to below the limits of industrial wastewater discharge in each cycle, and those in soils could be reduced by 53.8%, 58.8%, 25.5%, and 70.2% at the initial concentrations of 1549, 1016, 310 and 50 mg kg-1, respectively. The heavy metal removal rate increased with increasing current density in the range of 0-52 mA cm-2. This work provides an efficient and sustainable method for the remediation of site soils polluted by mixed heavy metals.
... Also, the two working electrodes in the same compartment are required to directly quantify the catalyst selectivity. The amperometric determination of ClO − evolved at WE 1 (i 2 ) has sensitivity comparable to that of the standard colorimetric N,N-diethyl-p-phenylenediamine assay, 55 and it allows a continuous determination as opposed to both colorimetric and chromatographic methods, which require periodical sampling of the electrolyte. The ClO − detection limit with our setup is approximately 9 μmol h −1 (6 ppm h −1 ; a detailed description is given in the Supporting Information), which is far below the quantity of O 2 electrogenerated by the catalysts, as reported in Figure 5f and the related discussion. ...
The direct electrolysis of seawater is greatly inhibited by the oxidation of Cl- to free chlorine, an undesirable, corrosive byproduct. To suppress the parasitic interference of Cl- and any other ion, we developed a freestanding, electrically conducting, 3D macroporous reduced graphene oxide (rGO) scaffold with cobalt oxide particles selectively deposited on the internal walls of its closed pores (with an average diameter of ∼180 μm). The pore walls act as membranes composed of stacked rGO flakes; the nanochannels between rGO layers (size <1 nm) are permeable to water and gases while preventing the diffusion of dissolved ions such as Cl-. Due to this, the catalytic particles are selectively accessible to water molecules but not to ions, allowing electrolysis to occur without chlorine evolution. The electrodes developed exhibit a stable generation of O2 from simulated seawater at pH 14, reaching a specific current density of up to 25 A g-1 during continuous electrolysis with 89-98% Faradaic efficiency, while chlorine generation is below 6 ppm h-1, the sensitivity limit of the detection method employed. The strategy here proposed can be generalized to build electrodes that are inherently selective thanks to their architecture, with catalytically active particles loaded into closed pores with selective ion transport properties.
... Although another chromogenic agent, o-dianisidine, has shown good sensitivity in chlorine determination, some recent investigations revealed that the reagent was unstable (Blecher and Glassman, 1962;Washko and Rice, 1961) and only able to achieve a narrow linear range (0.05-1.3 mg L −1 Cl 2 ) (Icardo et al., 2001a;Saad et al., 2005). The DPD method is still the most reliable chlorine residual measurement method and is employed in most colourimetric-based chlorine systems (Carlsson et al., 1999;Gordon et al., 1991;Harp, 2002;Moberg and Karlberg, 2000;Wilson et al., 2019). ...
During the COVID-19 pandemic, the use of chlorine-based disinfectants has surged due to their excellent performance and cost-effectiveness in intercepting the spread of the virus and bacteria in water and air. Many authorities have demanded strict chlorine dosage for disinfection to ensure sufficient chlorine residual for inactivating viruses and bacteria while not posing harmful effects to humans as well as the environment. Reliable chlorine sensing techniques have therefore become the keys to ensure a balance between chlorine disinfection efficiency and disinfection safety. Up to now, there is still a lack of comprehensive review that collates and appraises the recently available techniques from a practical point of view. In this work, we intend to present a detailed overview of the recent advances in monitoring chlorine in both dissolved and gaseous forms aiming to present valuable information in terms of method accuracy, sensitivity, stability, reliability, and applicability, which in turn guides future sensor development. Data on the analytical performance of different techniques and environmental impacts associated with the dominated chemical-based techniques are thus discussed. Finally, this study concluded with highlights of gaps in knowledge and trends for future chlorine sensing development. Due to the increasing use of chlorine in disinfection and chemical synthesis, we believe the information present in this review is a relevant and timely resource for the water treatment industry, healthcare sector, and environmental organizations.
... In addition, the distribution of a sensor matrix or network is generally set in a water pipe system or water source so that comprehensive information on water quality can be conveniently obtained; these systems require sensors to have satisfactory long-term stability and some ability for self-cleaning in complex water compositions. Thus, many methods/sensors for free chlorine detection, such as laboratory contaminant analysis and colorimetric contaminant detection, have difficulty meeting the demands of gridding and distributed free chlorine monitoring 6,7 . Electrochemical sensors have many advantages, such as their smaller size and fast response time; thus, their use is considered a possible strategy for the online monitoring of tap water. ...
Free chlorine is one of the key water quality parameters in tap water. However, a free chlorine sensor with the characteristics of batch processing, durability, antibiofouling/antiorganic passivation and in situ monitoring of free chlorine in tap water continues to be a challenging issue. In this paper, a novel silicon-based electrochemical sensor for free chlorine that can self-clean and be mass produced via microfabrication technique/MEMS (Micro-Electro-Mechanical System) is proposed. A liquid-conjugated Ag/AgCl reference electrode is fabricated, and electrochemically stable BDD/Pt is employed as the working/counter electrode to verify the effectiveness of the as-fabricated sensor for free chlorine detection. The sensor demonstrates an acceptable limit of detection (0.056 mg/L) and desirable linearity (R2 = 0.998). Particularly, at a potential of +2.5 V, hydroxyl radicals are generated on the BBD electrode by electrolyzing water, which then remove the organic matter attached to the surface of the sensor though an electrochemical digestion process. The performance of the fouled sensor recovers from 50.2 to 94.1% compared with the initial state after self-cleaning for 30 min. In addition, by employing the MEMS technique, favorable response consistency and high reproducibility (RSD < 4.05%) are observed, offering the opportunity to mass produce the proposed sensor in the future. A desirable linear dependency between the pH, temperature, and flow rate and the detection of free chlorine is observed, ensuring the accuracy of the sensor with any hydrologic parameter. The interesting sensing and self-cleaning behavior of the as-proposed sensor indicate that this study of the mass production of free chlorine sensors by MEMS is successful in developing a competitive device for the online monitoring of free chlorine in tap water.
... 18 The oxidation of N,N-diethyl-p-phenylenediamine (DPD) by free chlorine to generate a reddish solution and the subsequent measurement of the absorbance is the most popular approach to determine its concentration in water. [19][20][21] However, because of the extensive use of free chlorine as a disinfectant, many other quantication strategies have been reported. 14 Examples of other reagents for colorimetric detection include ABTS, 22 Michler's thioketone, 23 and syringaldazine. ...
Free chlorine is the most commonly used water disinfectant. Measuring its concentration during and after water treatment is crucial to ensure its effectiveness. However, many of the existing methods do not allow for continuous on-line monitoring. Here we demonstrate a solid state chemiresistive sensor using graphene-like carbon (GLC) that overcomes that issue. GLC films that were either bare or non-covalently functionalized with the redox-active phenyl-capped aniline tetramer (PCAT) were successfully employed to quantify aqueous free chlorine, although functionalized devices showed better performance. The response of the sensors to increasing concentrations of free chlorine followed a Langmuir adsorption isotherm in the two tested ranges: 0.01–0.2 ppm and 0.2–1.4 ppm. The limit of detection was estimated to be 1 ppb, permitting the detection of breaches in chlorine filters. The devices respond to decreasing levels of free chlorine without the need for a reset, allowing for the continuous monitoring of fluctuations in the concentration. The maximum sensor response and saturation concentration were found to depend on the thickness of the GLC film. Hence, the sensitivity and dynamic range of the sensors can be tailored to different applications by adjusting the thickness of the films. Tap water samples from a residential area were tested using these sensors, which showed good agreement with standard colorimetric measurement methods. The devices did not suffer from interferences in the presence of ions commonly found in drinking water. Overall, these sensors are a cost-effective option for the continuous automated monitoring of free chlorine in drinking water. This journal is
... Before photoirradiation, the air was flowed for 30 min to achieve adsorption/desorption equilibrium between an aqueous NaCl solution and the photocatalyst, and then, the light source was turned on to expose the whole reaction system to visible light. After 2 h of photoirradiation, the yield of HClO was measured by the DPD method [27]. It is established that the DPD reagent (Hangzhou Luheng Biotechnology Co. Ltd., China) is transformed by HClO into an oxidized form, which exhibits an absorbance at 552 nm. ...
The hypochlorous acid (HCIO) was synthesized from seawater by the Pt/WO3 photocatalyst under visible-light irradiation. The effect of WO3 morphology and Pt loading on the performance of the composite photocatalyst for the production of HCIO has been studied in detail. The study found that among the series of materials, hollow WO3 microspheres with a diameter of about 3 μm loaded with 1.0 wt% Pt have the best HCIO production performance. Over it, 14.52 μM of HClO (1.24 mg/L of free chlorine) was accumulated in 0.5 M NaCl solution after 2 h of visible-light photoirradiation. What is more, the concentration of HClO can reach 4.34 μM (0.354 mg/L free chlorine) in natural seawater for 1 h using this Pt/WO3 photocatalyst. Under visible-light irradiation, the Pt/WO3 photocatalyst has a good broad-spectrum antibacterial activity and the activity of inhibiting marine fouling algae. The Pt/WO3 photocatalyst has high stability and reusability. All these characteristics are conducive to the application in the field of marine antifouling. Moreover, the photocatalytic reaction mechanism was evaluated by studying the photoelectrochemical properties of Pt/WO3/FTO. This research provides a new strategy for replacing the traditional electrolytic marine antifouling system with the visible-light-catalyzed HClO production system.
... Free chlorine readily reacts with DPD, while chloramines require the addition of potassium iodide in order to catalyse the reaction. Iodide reacts with chloramines to form triiodide ion, which consequently reacts with DPD [5,9,11]. However, this method has serious disadvantages, in particular that it requires the use of expensive chemicals and results in the production of a waste stream that cannot be released into the environment without further processing [9]. ...
Chlorine is a widely used disinfectant and oxidant used for an array of municipal and industrial applications including potable water, swimming pools, and cleaning of membranes. To most popular method to verify the concentration of free chlorine is the colorimetric method based on DPD (N, N-diethyl-p-phenylenediamine) which is fast and reasonably cheap, but DPD and its product are potentially toxic. Therefore a novel, environmentally friendly colorimetric method for the quantification of residual chlorine based on the food additive, pyridoxamine (4-(aminomethyl)-5-(hydroxymethyl)-2-methylpyridin-3-ol) was investigated. Pyridoxamine is a B6 vitamin with an absorption maximum at 324 nm and fluorescence emission at 396 nm. Pyridoxamine reacts rapidly and selectively with free chlorine resulting in linear decrease both in absorbance and in emission, giving therefore calibration curves with negative slope. The pyridoxamine method was successfully applied for the quantification of free chlorine from 0.2 mg/L to 250 mg/L. Using 1 cm cuvettes, the limit of quantification was 0.12 mg Cl2/L. The pyridoxamine and the DPD methods were applied to actual environmental samples and the deviation between results were 4% to 9%. While pyridoxa-mine does not react with chloramine, quantification of monochloramine was possible when iodide was added, but the reaction is unfavourably slow.
... Colorimetric and fluorometric methods need reagents or optical systems which are complicated in some cases. [23][24][25][26] On the other hand, electrochemical methods have many advantages such as non-reagent type, simplicity, low cost, and robustness. Most of them are amperometric-type sensors using various unique materials such as carbon nanotubes, 27,28 gold nanoparticles, 29 Prussian blue, 30 ammonium carbamate modified graphite, 31 and polymelamine. ...
Chlorine disinfection of water is one treatment method to supply safe tap water. The quantitative monitoring of free chlorine concentration as an important water quality index is effective to maintain tap water hygienic safety. In this study, a simple potentiometric sensor which is composed of two dissimilar metal electrodes (a pair of platinum and austenitic stainless steel: SUS316) was evaluated in synthetic and actual tap water. It was demonstrated that the open circuit potential of each electrode had a different sensitivity to free chlorine and that the difference could be extracted as the sensing signal without using conventional reference electrodes. In a flowing system using tap water, more than 300 mV of large sensor signal and good reproducibility were observed at a free chlorine concentration of 0.6 mg l ⁻¹ . The long-term baseline drift was within the range of ±10 mV and the sensor was almost immune to various environmental factors such as temperature, pressure, flow rate, and conductivity, but not for pH. These results would pave the way to develop various sensor applications that could be directly applied to tap water pipelines for continuous in-line monitoring of residual chlorine with low cost and maintenance.
... A large number of analytical methods have been developed for determination of free chlorine in water including ion chromatography [12], chemiluminescence [13], fluorescence [14], amperometry [15], and spectrophotometry [16]. Of all methods, the most commonly used one is a colorimetric method, which is based on the reaction of N, N-diethyl-p-phenylenediamine (DPD) reagent [17,18] and analysis of free chlorine by spectrophotometer. However, the application of conventionally spectrophotometric technique is suffered from some drawbacks, such as nonportability of laboratory instrument and low capability for real-time or on-line monitoring. ...
... The photocurrent density promoted by the external bias reached 0.55 mA cm −2 at a cell voltage of 0.5 V, which was approximately five times higher than that with no external bias. The amount of OBS generated under the constant current condition (0.25 mA cm −2 ) was quantitatively determined by the N,N-diethyl-p-phenylenedi- amine (DPD) method, and it was found to be 0.74 μmol, 38 which gave 98% for the faradaic efficiency (defined by eq 1) in step 1. Br − was oxidized to Br 2 on the BiVO 4 /WO 3 /FTO photoelectrode and then was disproportionated to form HOBr in a neutral aqueous solution. 39 Consequently, the strong absorbance peaks of Br 3 − (Br 2 + Br − , 0.39 μmol) as well as the weak absorption of HOBr (0.08 μmol) and Br 2 (0.27 μmol) were observed at around 266, 260, and 390 nm, respectively ( Figures S4 and S5). ...
Hypochlorous acid (HClO) is released by immune cells in the immune system, and it helps the body fight off infections and inflammation by killing bacteria, viruses, and other pathogens. However, tissue damage or apoptosis may also be induced by excess HClO. On this basis, we designed the probe TPE‐NS by choosing tetraphenylethylene (TPE) as the luminescent unit and dimethylthiocarbamoyl chloride as the recognition site. By Gaussian's transition state calculations, HClO will cut off the photoinduced electron transfer (PET) effect of TPE‐NS by hydrolysis reaction, thus emitting strong fluorescence. TPE‐NS has rapid recognition and excellent specificity for HClO, and the limit of detection is 7.27 μM. Finally, TPE‐NS was successfully used for the visualization of endogenous and exogenous HClO in cell experiments.
The utilization of chlorine-based ballast water treatment systems is essential for preventing the spread of invasive species, making the continuous monitoring of total residual oxidant (TRO) levels imperative for compliance with environmental regulations. This study developed and optimized a phosphate buffer-sulfuric acid-based solution (PSS) for use in the N, N‒diethyl‒p‒phenylenediamine (DPD) colorimetric method to determine TRO in ballast water. Batch experiments demonstrated that pH 6 is the optimal phosphate buffer condition. Furthermore, the addition of iodide ions promoted rapid and stable TRO measurements across various conditions including pH and ammonium concentrations, sodium hypochlorite (NaOCl) concentrations, temperature, suspended solids (SS), natural organic matter (NOM), and water types. The optimized PSS achieved TRO measurement accuracy within ±5% of reference values, notably surpassing the commercial citrate buffer-p‒toluenesulfonic acid-based solution (CTS), especially under challenging conditions such as low NaOCl concentrations, higher temperatures, and the presence of SS. PSS exhibited an average error rate of 3.16%, compared to 4.44% for CTS. Field tests at a ballast water treatment facility further confirmed the reliability of PSS for real-time TRO monitoring. This optimized reagent provides a practical, cost-effective solution for ballast water treatment systems, supporting environmental protection and regulatory compliance.
Environmental conservation is a worldwide concern, that has necessitated the development of analytical systems free from harmful chemicals. This paper reports a new residual chlorine sensor utilizing track-etched membrane platinum electrodes with an inserted activated carbon chamber. Differences in electrode potential before and after passing through the activated carbon chamber indicate the quantity of substances adsorbed or decomposed by the activated carbon. The sensor system, integrated into a continuous flow analyzer, exhibited a linear correlation between the potential difference and the logarithm of hypochlorous acid concentration within the range of 0.1 to 50 μM. This proposed method is an exemplary model for a novel flow-through potentiometric sensor design comprising adsorbent and filter electrodes.
A novel sustained chlorine-releasing polydimethylsiloxane/Ca(ClO)2 (PDMS/Ca(ClO)2) material was fabricated by encapsulating Ca(ClO)2 in a PDMS matrix due to its high hydrophobicity and high chemical stability, which showed immediate-responsive and long-lasting antibacterial capabilities in aqueous conditions. Free chlorine could be released from the PDMS/Ca(ClO)2 after immersion in water for 2 min and could also be sustainedly released for 2 weeks, while the released concentration is negatively related to the duration time and positively with the initial Ca(ClO)2 contents. Additionally, Ca(ClO)2 powder as a filler significantly affects the crosslinking and pore size of PDMS. The PDMS/Ca(ClO)2 materials exhibited enduring antibacterial performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in both planktonic and multispecies-biofilm status. It is expected that this PDMS/Ca(ClO)2 material and its similar composite would be promising candidates for wide sustainable disinfection applications in biomedical and industrial fields.
The adoption of chlorine in drinking water disinfection with the determination of residual chlorine in the form of hypochlorite ion (ClO-) is in widespread demand. Several sensors 15including colorimetric, fluorometric, and electrochemical methods are currently in use, but 16detection limits and ease of application remain a challenge. In this work, two new cyanine derivatives-based ClO- sensors, that were prepared by solvent-free microwave synthesis, are reported. The two sensors are highly sensitive and selective to ClO-, exhibiting a noticeable color change visible to the naked eye. Additionally, the sensors can detect ClO- without interference from other potential water pollutants, with low detection limits of 7.43 ppb and 0.917 ppb based on absorption performance. When using fluorometric methods, the sensors' detection limits are pushed down to 0.025 ppb and 0.598 ppb for sensors I and II, respectively. The sensors can be loaded with paper strips for field and domestic detection of ClO- in tap water treatment installations. Using the quartz crystal microbalance (QCM) technique, these sensors showed strong detection sensitivity to ClO-, with detection limits of 0.256 ppm and 0.09 ppm for sensors I and II, respectively. Quantum chemical studies using density functional theory (DFT) 27calculations, natural bond orbital (NBO) analysis, molecular electrostatic potential (MESP), and time-dependent density functional theory (TD-DFT) supported the findings. The sensing 29mechanism is rationalized in terms of radical cation formation upon ClO- oxidation of cyanine 30sensors I and II.
Sodium dichloroisocyanurate (Na-DCC), a disinfectant known for rapid decomposition in water, loses its effectiveness with complete release of free available chlorine (FAC) in under an hour. To overcome this, a series of chlorine rich transition metal complexes/tetrabutylammonium (TBA) salts of DCC, including 2Na[Cu(DCC)4], 2Na[Fe(DCC)4], 2Na[Co(DCC)4]·6H2O, 2Na[Ni(DCC)4]·6H2O, and TBA[DCC]·4H2O have been developed for extended chlorine release studies. The DCC-salts are synthesized based on the metathesis reaction process and are characterized using IR, NMR, CHN analyses, TGA,DSC, and Lovi bond colorimeter. The DCC-salts displayed poor water solubility and low decomposition chlorine release profile compared to Na-DCC. The water solubility of DCC-salts was reduced by a factor of 5.37 to 2500 compared to Na-DCC. The decomposition release of FAC from DCC-salts has been studied over time in comparison to Na-DCC in distilled water using a Lovi-bond colorimeter. DCC-salts displayed controlled FAC release profiles that varied from 1-13 days depending on the type of metal/TBA unit in them, whereas the parent Na-DCC displayed complete FAC release in about 0.91 h. For a proof of concept, the controlled release of metal from one of the DCC-metal complex salts, i.e., copper from the Cu-DCC is also investigated with a function of time in distilled water at RT. The 100% release of copper from Cu-DCC was identified over a period of 10 days. In addition, the applicability of DCC-salts as excellent antiviral agents against the bacteriophage T4 and antibacterial agents against Erwinia, Pseudomonas aeruginosa PA014 (Gram-negative), and Staphylococcus epidermidis (Gram-positive) compared to Na-DCC has been demonstrated.
Chloride ion (Cl-) is one of the most common anions in wastewater and saline wastewater, but its elusive effects on organics degradation are not clear yet in many cases. In this paper, the effect of Cl- on organic compounds degradation is intensively studied in catalytic ozonation of different water matrix. It was found that the effect of Cl- is almost completely reflected by transforming ·OH to reactive chlorine species (RCS), which is simultaneously competitive with organics degradation. The competition between organics and Cl- for ·OH directly determines the ratio of their consumption rate of ·OH, which depends on their concentration and reactivity with ·OH. Especially, the concentration of organics and solution pH may change greatly during organics degradation process, which will correspondingly influence the transformation rate of ·OH to RCS. Therefore, the effect of Cl- on organics degradation is not immutable, and may dynamically change. As the reaction product between Cl- and ·OH, RCS was also expected to affect the degradation of organics. But we found that Cl· had no significant contribution to the degradation of organics in catalytic ozonation, which may due to its reaction with ozone. Catalytic ozonation of a series of benzoic acid (BA) with different substituents in chloride contained wastewater was also investigated, and the results showed that the electron-donating substituents can weaken the inhibition of Cl- on BAs degradation, because they increase the reactivity of organics with ·OH, O3 and RCS.
The shortage and pollution of drinking water are becoming severe problems in many parts of the world. Sanitary water supply is a vital issue for human life. For water disinfection, it is essential to control the concentration of free and combined chlorine appropriately. The authors constructed a flow injection analysis (FIA) system to simultaneously determine free and combined chlorine based on the difference in the photolysis reaction rate. The proposed system contained a Y-branch to separate the injected sample solution into light-irradiated and non-light-irradiated channels. The signals derived from the sample solution, divided into these channels, were detected individually with a time difference, and the simultaneous determination with a single sample injection became available. This study demonstrated the simultaneous determination of hypochlorite ion and chloramine T in the mixture using a pair of simultaneous equations based on pre-prepared relationship curves. The analytical results obtained by the proposed system coincided with the added amount in the mix.
Chlorination of seawater forms a range of secondary oxidative species, collectively termed “chlorine-produced oxidants” (CPOs). These compounds do not have the same biocidal efficacy, the same fate and behavior in the marine environment, the same potential formation of chlorination by-products (CBPs), nor the same effects on marine organisms. Their chemical speciation is an important step toward an accurate assessment of the effectiveness of chlorination and the potential impacts of its releases, among others. The aim of this paper - which is the second of a trilogy dedicated to the chemical speciation of CPOs in seawater - is to cover all aspects related to CPOs analysis in seawater, from sampling to instrumental determination. First, it discusses the procedures involved in synthesis, storage, and standardization of analytical standards. Second, it deals with sampling and sample preparation, addressing all relevant issues related to these two key steps. Third, it provides a comprehensive and up-to-date overview of the colorimetric, titrimetric, and electrochemical methods used for CPOs determination and thoroughly discusses their advantages and limitations. Finally, this review ends with some recommendations for progress in the field of CPO analysis with the three aforementioned approaches. Chromatographic and mass spectrometric-based methods will be covered in the third and final article (Part III).
For the optical equipment used in the marine environment, the quality and accuracy of the tests are easily affected by biological fouling. Hence, good anti-fouling performance is crucial for preserving the optical equipment. A new electrochemical chlorination anti-fouling system has been proposed for years and is suitable for underwater optical windows. In this paper, nano Co3O4 electrocatalysts with different morphologies were prepared through the hydrothermal method to study the structure–activity relationship between their electrochemical properties and morphologies. The nanourchin Co3O4 shows the best electrochemical properties resulting from its large surface area. The titanium mesh electrode with nanourchin Co3O4 was used to evaluate the anti-fouling performance. In comparison to commercial dimensionally stable anode electrodes, the developed Co3O4/titanium mesh electrode has higher catalytic performance, better selectivity, and lower cost. The bactericidal rate can reach 95% in 20 mins and it can effectively inhibit the sedimentation of microorganisms on the glass surface. Therefore, it is a promising strategy to use the nanourchin Co3O4 as an electrocatalyst to protect the underwater optical windows.
Seawater is a cost-effective and abundant electrolyte used as an electrode rinse solution to enable optimum utilization of reverse electrodialysis (RED). However, it is associated with several limitations, including the use of precious electrode materials, and its long-term stability must be addressed prior to its application in the field of seawater technology. In this context, a novel RED based on carbon electrodes was designed, and the experimental conditions were optimized for maximizing the harvesting of energy with aquaculture wastewater disinfection and recycling. The power obtained by RED, with a current density of 30 A/m² and a flow rate of 424 mL/min, designed by response surface methodology, was in good agreement with the predicted maximum power density (0.64 W/m²). The treatment was sustainable, mainly due to an anodic reaction of electro-generated sodium hypochlorite (NaOCl) under natural conditions, which afforded a high disinfection efficiency (above 99.5 ± 0.2% within 1 min under continuous flow (pH 8)), even under real seawater conditions and in aquaculture wastewater. Simultaneously, a stable power of 0.1 ± 0.03 W (0.25 ± 0.07 W/m²) generated a reasonable specific energy (within 0.02 kWh/m³). Inorganic fouling was efficiently suppressed using a surface-modified carbon cathode for 680 h. Thus, the on-site seawater disinfection by RED described herein is practically feasible and could offer a sustainable and energy-efficient alternative to seawater recycling.
We developed a porous diamino group-functionalized Zr(IV) metal-organic framework (MOF). The synthesized MOF has a similar structure to DUT-52 (DUT = Dresden University of Technology), which has a face-centered cubic structure with an Fm3̄m space group. The synthesized material (DUT-52-(NH2)2-1) was solvent exchanged with methanol (MeOH) and activated at 100 °C overnight. Both the as-synthesized and activated materials (DUT-52-(NH2)2-1') are thermally stable until 300 °C. The Brunauer-Emmett-Teller (BET) surface area of DUT-52-(NH2)2-1' was found to be 413 m2 g-1. DUT-52-(NH2)2-1' showed a significant quenching of fluorescence response after coming in contact with free chlorine (ClO-) in an aqueous medium. The selectivity of DUT-52-(NH2)2-1' towards ClO- was not significantly hampered in the presence of any competitive ion. The limit of detection (LOD) value was found to be 0.08 μM in phosphate-buffered saline (PBS, pH = 7.4). DUT-52-(NH2)2-1' is recyclable and very sensitive towards ClO-. Moreover, the paper strip method was developed for onsite identification of ClO-. Furthermore, the catalytic activity of DUT-52-(NH2)2-1' was tested in the Knoevenagel condensation between benzaldehyde and cyanoacetamide. The experimental results clearly indicate that DUT-52-(NH2)2-1' exhibits high activity with very high selectivity towards condensation products. The solid was reusable three times with no decay in its activity, as evidenced by powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM) and fourier transform infrared (FT-IR).
Hypochlorous acid (HClO) as a high value-added oxidation reagent is produced conventionally by a chlor-alkali electrolysis process, which causes a heavy economic burden and leads to considerable CO2 emissions. Herein, we reported the photocatalytic production of HClO by oxidation of chloride (Cl⁻) in a dilute saline solution close to that of seawater over various dual cocatalyst-loaded WO3 powder photocatalysts using visible light as the energy source. The activities were improved more than twice by co-loading of Mn compared to the standard Pt/WO3. A maximum HClO formation rate of 37 μmol h⁻¹ (about 2.6 ppm) was achieved when using Pt-Mn dual catalyst loaded WO3, which is effective for inactivation of various bacteria and fungi in drinking water. The photochemical and electrochemical studies revealed that the synergistic effect between Pt and Mn could not only promote the decomposition of H2O2 derived from the oxygen reduction reaction, but also increase the selectivity for oxidation of Cl⁻ into HClO. This Pt-Mn dual cocatalyst modification strategy opens up prospects for efficient and economical production of HClO based on visible light energy.
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).
Fresh produce are typically washed in a flume washer to inactivate bacteria from produce surface and the typical sanitizer employed by produce processors is chlorinated water. The distribution of free chlorine in a flume washer was simulated and validated using experimental data. The influences of free chlorine injection velocity and the presence of soluble organic matter on the spatial distribution of free chlorine were investigated. At lower injection velocity, the chlorine was more concentrated near the bottom of the flume compared to the middle of the flume. The presence of soluble organic matter depleted the free chlorine in the flume. The experimental data on free chlorine concentrations were in reasonable agreement with the numerically predicted free chlorine concentrations. Turbulent fluid flow in an industry-scale flume washer was simulated. At lower main flow velocity (0.1 m/s) and higher free chlorine injection velocity (0.5 m/s), and when the injection direction was perpendicular to slanted side faces of the flume, the distribution of free chlorine was more uniform compared to other injection strategies.
In order to limit various alien species by ballast water, electrolysis of ballast water is used to sterilize microorganisms. In this process, total residual oxidizer (TRO) is produced, and it is necessary to measure the precise TRO concentration to prevent excessive disinfection by-products and limit emissions. In this TRO concentration measurement system, a white LED module and RGB sensor are used to measure the absorbance through the DPD colorimetric method. The intensity of LED light has a little error for each LED module. In addition, the effect of LED aging in which the intensity of the light source decreases with the elapsed time. For this reason, the TRO concentration measurement error increases. To solve this problem, we propose an LED module calibration algorithm by current PI control and an optimal LED operation time derivation to reduce the effect of LED aging. A large number of LED modules were applied to various seawater environments. In the conventional method, the measurement accuracy and precision of the average TRO concentration were 6.56% and 9.54%, respectively, and measurement accuracy and precision through the proposed algorithm and LED aging optimization were greatly reduced to 0.10% and 0.85%, respectively. In addition, we derived that LED aging was minimized when the measurement time of LED light was 1 s and the turn-off time of the LED light was 10 s. Through these experimental results, we confirmed that the non-uniform LED light is improved by the proposed algorithm. Furthermore, the standard values for TRO concentration measurement (accuracy: less than 5%, precision: less than 2%) were satisfied.
A mixture of polydopamine (PDA) and polyethyleneimine (PEI) are used as the adhesive, wetting, and reducing agent simultaneously to fabricate a conductive silver membrane. The conformal coating of PDA/PEI on individual polypropylene fibers of polypropylene micromembrane (PPMM) renders the latter to be hydrophilic for subsequent electroless silver deposition. The resulting conductive silver membrane demonstrates impressive electric conductivity in both X and Z directions. The thickness of conformal silver overcoat is 250 nm and the effective loading is 2.4 mg/cm². The mechanical strength of conducive silver membrane is similar to that of pristine PPMM. Both cyclic voltammetry and impedance spectroscopy on the conductive silver membrane reveal a large electrochemical active surface area. To validate its usefulness as a robust soft electrode, the conductive silver membrane is evaluated for the detection of chlorine in aqueous solution in which a low detection limit of 0.07 ppm and a wide detection range of 0.1~20 ppm are validated.
Distributions of halogenated disinfection byproducts (DBPs) in a two-source water distribution system (WDS) with enhanced chlorination were investigated. The WDS was divided into different sub-service areas based on different electrical conductivity of two water sources. Results clearly show that the principal halogenated DBPs were trihalomethanes (THMs) (5.06-82.69 μg/L), varying within the concentration range as 2-5 times as the levels of haloacetic acids (HAAs) (1.41-61.48 μg/L) and haloacetonitriles (HANs) (0.21-15.13 μg/L). Different water sources, treatment trains, and enhanced chlorination within the WDS had significant effects on seasonal and spatial variations of the DBP distributions over water conveyance. THM and HAA formation followed the sequence of summer > autumn > winter > spring. On the other hand, the DBP spatial distributions were visualized using the ArcGIS enabled Inverse distance weighting technique. The superposition of different DBP spatial distributions allowed for the identification of the high-risk THMs and HAAs areas based on the average values of THMs (27.49 μg/L) and HAAs (14.06 μg/L). Beyond the comprehensive analyses of DBP distribution in a municipal WDS, the project proposed and validated an innovative methodology to locate the DBP high-risk areas and to reveal the effects of different factors on DBPs distribution in a two-source WDS.
A selective electrocatalytic system for the exhaustive conversion of inorganic nitrogen to nitrogen gas (N2) is developed, whereby the total nitrogen (TN) removal and N2 selectivity achieve 96.8% and 99.6% in 120 min, respectively. Cyclic voltammetry reveals the feasibility of electrooxidative chlorination of NH4⁺ compared to direct anodic oxidation. The TN removal is ranging from 96.2% to 99.7% under various inorganic nitrogen ratios. Green rust (GR) of mixed Fe(II)-Fe(III) hydroxides is identified at cathode surface by in-situ Raman analysis, donating electrons to NO3⁻. Direct electron reduction, indirect atomic H* reduction, and GR induced reduction are integrated for the rapid NO3⁻ conversion at cathode interface. Treatment of authentic wastewater of nickel plating in continuous running further demonstrates the superiority and durability of the electrochemical system for both NO3⁻ and TN abatement. The electrochemical system has potential for efficient and stable nitrogen pollutants removal in the high-salinity wastewater.
Photocatalytic production of hypobromous acid (HBrO) by oxidation of bromide (Br ⁻ ) under simulated solar light was successfully obtained over visible-light active photocatalysts. Among all photocatalysts, the platinum (Pt) cocatalyst-loaded tungsten...
The diethyl-p-phenylene diamine (DPD) titrimetric and colorimetric methods have been internationally evaluated and accepted as standard procedures for the determination of free and combined chlorine residuals in water. The methods also provide a clear-cut determination of free available chlorine (FAC), the most active disinfectant of these chlorine species. This paper discusses experiments designed to evaluate the extent of the monochloramine interference in FAC determinations using correctly prepared standard reagents, and to provide a comparison of the results with those obtained using non-standard reagents from which mercuric chloride and EDTA were omitted.
The reaction kinetics of monochloramine (NH2Cl) and N,N-diethyl-p-phenylenediamme (DPD) were studied. The method of initial rates was used to study the rate of formation of a colored intermediate product and the rate of fading of that product to colorless end products. Equilibrium constants were determined for protonated and nonprotonated DPD and the intermediate products. The reaction is first order with respect to both NH2Cl and DPD and showed a complex order with respect to pH. This study confirmed that NH2Cl oxidizes DPD to the colored intermediate at a rate of 5.6 and 6.0% of the NH2Cl concentration, in the first minute, at 25°C and 5 × 10-5 M (3.5 mg as Cl2/L) and 1 × 10-4 M (7.0 mg as Cl2/L) NH2Cl, respectively.
In the determination of free and combined chlorine, the reaction of permanganate standards with N,N-diethyl-p-phenylenediamine (DPD) exhibits nonlinearity presumably because both the colored semiquinoid product and the colorless quinoid product are both formed. The titrimetric DPD method titrates both of the products while the colorimetric method monitors only the colored semiquinoid products. This results in a nonlinear response for the colorimetric method above 1.0 mg/l. as Cl(2). Under FIA conditions, the nonlinearity of the DPD colorimetric method is eliminated in the 0.1-5.0 mg/l. (as Cl(2)) range and the linear range is expanded to 0.1-8.0 mg/l. as Cl(2). Also, relative standard deviations are improved by 0.5-11% relative to the colorimetric method and 1.5-4.0% relative to the titrimetric method. The FIA method was developed further to sequentially determine both free and combined chlorine, since chloramine was found to have a negligible interference in the free chlorine determination.
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