Chlorine In Aqueous Solution Research Articles

Simple and Selective Determination of Free Chlorine in Aqueous Solutions by an Electrophilic Aromatic Substitution Reaction Followed by Liquid Chromatography Coupled with Mass Spectrometry

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.

CuO-ZIF-8 modified electrode surface as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work has applied metal–organic frameworks (MOFs) with high adsorbability and catalytic activity to develop electrochemical sensors to determine free chlorine (free-Cl) concentrations in aqueous media. A zeolitic imidazolate frameworks, Zn(Hmim)2 (ZIF-8) has been synthesized and incorporated with CuO nanosheets to decorate a glassy carbon electrode (GCE) and provide a new sensor for free-Cl determination. The as-prepared ZIF-8 and CuO-ZIF-8 composites have been characterized by FESEM, EDX, XRD, and FT-IR analyses. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) utilized to characterize the CuO-ZIF-8/GC modified electrode electrochemically, demonstrated the ability of the sensor to measure free-Cl concentration. Using differential pulse voltammetry (DPV) and under the optimal conditions, the prepared CuO-ZIF-8/GC modified electrode showed a linear response in the 0.25–60 ppm range with a 12 ppb detection limit (LOD) for free-Cl concentration. Finally, the fabricated sensor was applied to analyze free-Cl from actual swimming pool water samples with promising 97.5 to 103.0% recoveries.

Hydroxyl-aluminum pillared bentonite enhanced Mn(II) removal by chlorine oxidation

Al-PILC was used to catalyze the chlorine oxidation of Mn(II) in aqueous solution. The effects of various catalysts, catalyst dosage, chlorine dosage, pH value, temperature and organic content on the oxidation process were investigated. Results show that 1.5 mg/L chlorine can quickly oxidize Mn(II) from 0.5 mg/L to less than 0.04 mg/L with 10 mg/L Al-PILC. Using catalysts with higher porosity and higher SA, increase in chlorine concentration, increase in catalyst dosage, higher pH, and higher temperature can significantly enhance the rate of Mn(II) catalytic oxidation. The Mn(II) oxidation process includes the homogeneous oxidation, catalytic oxidation on the surface of the catalysts and self-catalytic oxidation produced by the newly produced MnOx. Al-PILC surface provides active sites for chlorine oxidation Mn(II) in the water, and also provides binding sites for the newly produced MnOx, which has higher catalytic activity and thus has an self-catalytic oxidation effect. The higher the porosity and SA of Al-PILC, the more catalytic oxidation active sites and loading sites, and the better the catalytic oxidation effect. The study promotes the understanding of chlorine catalyzed oxidation Mn(II) in aqueous solution, but also provide important guide to study newly efficient catalysts to oxidize Mn(II) with chlorine in aqueous solution.

First Report of Neoscytalidium dimidiatum causing leaf zonate spot disease of Aloe vera L. in China.

In February 2022, leaf zonate spot disease afflicted Aloe vera L. in Yunnan, China, endangering the $39 billion industry with 0.33ha under cultivation (Wan 2015). The disease manifested with watery spots progressing into oval or circular necrosis lesions, characterized by a dark center surrounded by a gray-brown zone. In the late stage of the disease, lesions regress in size and several small dark picnidia dots appeared on the gray-brown zone. The disease incidence ranged from 10% to 15% in three commercial plantations. If left uncontrolled, the disease could diminish the commercial value of Aloe vera plants. Eighteen symptomatic leaf samples underwent morphological and genetic identification. The samples were carefully washed with distilled water and 1×1 cm2 sections of tissue were excised using a sterile scalpel. The sections underwent surface-disinfection with 3% NaOCl for 3 min and 75% ethanol for 30 s. After three sterile water rinses the sections were air-dried. Subsequently, they were transferred to potato dextrose agar (PDA) before being incubated at 25 ℃ in the dark. Of the 18 samples, eight produced the colonies with similar morphological characteristics, named LH7. Isolate LH7 had downy to woolly aerial mycelia, initially pinkish white on the surface, and gradually turned greenish-olivaceous from the middle, and eventually turned dark brown to black after seven days. The fungus formed arthric chains in the aerial mycelium on PDA but did not produce conidiomata. The conidia, which occurred in arthric chains were 5.50-9.9 × 4.08-7.51 μm (mean 7.09× 5.26 μm, n=50) in size, cylindrical, brown, and 0-1 septate. To ascertain LH7's pathogenicity, three healthy one-year old aloe plants were surface-sanitized with a 1% aqueous chlorine solution, rinsed with sterile water, and dried. Three leaves from each plant were punctuated and inoculated using conidial suspension (100 μl of 1x 106 conidial mL-1), while three control plants were inoculated with sterile distilled water. The pathogenicity tests were repeated twice. The inoculated plants were kept at 25 ℃ with a 12-hour light/12-hour dark cycle. After seven days, symptoms observed in the field appeared in the plants, while no disease occurred in the control plants. After 21 days, conidiomata formed on the inoculated leaves, averaging 116.92 μm (n=20) in diameter. These conidiomata were globose to subglobose, and brown to sub-brown. The fungus was successfully re-isolated from symptomatic tissue and the resulting colonies were morphologically consistent with isolate LH7. Based on the characteristics, the fungus was identified as Neoscytalidium dimidiatum (Philips et al. 2013). The specimen was deposited in China Center for Type Culture Collection ( CCTCC AF 2024001). This identification was confirmed through sequencing of ITS gene region of rDNA using ITS1/ITS4 (Imran et al. 2022). The sequence was submitted into GenBank database (ON878059). BLAST analysis of the LH7's ITS amplicon showed 100% similarity with that of JN093303.1. A phylogenetic tree constructed using the maximum likelihood method revealed that ON878059 was clustered with JN093303.1. Previous studies have documented that pathogens such as Colletotrichum gloeosporioides (Penz.), Fusarium spp. and Rhizopus oryzae can also cause diseases in A. vera in China (Zhou et al. 2008; Ding et al. 2015). Additinonally, Cladosporium sphaerospermum, Pseudopestalotiopsis theae, and Lasiodiplodia theobromae have been identified as causal agents of aloe leaf spot diseases in India, Bangladesh and Malaysia (Avasthi et al. 2016; Ahmmed et al. 2022; Khoo et al. 2022). To our knowledge, this is the first report of N. dimidiatum causing leaf necrosis of aloe in China. Vigilant surveillance and disease control measures are imperative to mitigate potential losses in this region.

Cobalt-based metal-organic framework-functionalized graphene oxide modified electrode as a new electrochemical sensing platform for detection of free chlorine in aqueous solution

This work reports the profit of using a MOF compound for developing a sensitive electrochemical sensor to free chlorine detection in an aqueous solution. Co-MOF and FGO composites were synthesized and combined with the carbon paste (CP) to prepare an efficient electrochemical sensor with high sensing ability. The fabricated Co-MOF and FGO composites were characterized by SEM, EDX, FT-IR, and XRD techniques. Meanwhile, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were utilized to assess the electrochemical performance of the Co-MOF-FGO/CP modified electrode. Under the optimized condition, the amperometric detection showed that the reduction current of free chlorine increased linearly with a coefficient determination of 0.995 during its wide concentration range of 0.1–700 ppm. Also the detection limit (LOD) (S/N = 3) was 0.01 ppm. The selectivity of the sensor was tested with possible interferences, and satisfactory results were obtained. The proposed sensor was successfully used to determine the free chlorine in tap water and swimming pool water real samples. The results suggested that this proposed sensor could pave the way for developing the electrochemical sensor of free chlorine in aqueous media with MOFs.

First Report of Fusarium avenaceum Causing Postharvest Decay of European Pear in Mid-Atlantic United States.

Fruit losses due to postharvest decay caused by several fungal species is a major challenge for pear production (Sardella et al. 2016). In December 2021, a European pear (Pyrus communis L.) 'Dawn' with brown, circular, watery, and sunken lesions was observed in cold storage at the USDA Appalachian Fruit Research Station in Kearneysville, West Virginia. Only 1 of 14 'Dawn' pears examined in cold storage had the described disease symptoms. The fruit was surface sterilized, and symptomatic tissue was transferred to potato dextrose agar (PDA) and incubated at 25°C under continuous light. The isolate was hyphal tip purified and propagated on PDA plates at 25°C. The colonies grew an average of 8 mm/day and produced fluffy white aerial mycelium and pigmented rings of golden yellow which then darkened to pink with a dark pink on the reverse. The isolate was also cultured in liquid basal medium with carboxymethyl cellulose (Moura et al. 2020) for 7 days at 25°C to promote macroconidia formation. Macroconidia were slightly falcate with a tapering apical cell, usually 2 to 4 septate, and on average 16.8 µm long by 2.8 µm wide. The isolate was identified as Fusarium spp. based on morphology. Identity of the isolate was confirmed through sequencing of the ITS and TEF1 gene region (Stielow et al. 2015). The ITS and TEF1 sequences were deposited in GenBank (OP007197 and OP007198). BLAST analysis of the ITS amplicon identified multiple Fusarium spp. with 100% identity and 100% query coverage including F. avenaceum KJ562378. BLAST analysis of the TEF1 amplicon showed 99% identity and 99-100% query coverage with F. avenaceum isolates KM189442 and MK512754. Organic Bartlett pears were surface sanitized with a 1% aqueous chlorine solution, rinsed with sterile water and dried in a laminar flow hood. Fruit were then wounded with a sterile nail (4 mm diameter x 4 mm depth) and inoculated with a 4 mm mycelial plug taken from a 7- to 10-day old culture on PDA and wrapped with Parafilm. Plugs taken from sterile PDA were used as a control. Inoculated fruit were stored at 25°C in fruit trays in plastic bins for 7 days. Six fruit composed a replicate, and the experiment was repeated for a total of two replications. Lesions developed within 48 hours and expanded to an average of 28.5 mm by day 7. No lesions were observed on control fruit. Symptoms observed on inoculated pears were the same as the decay observed on the original pear obtained from cold storage. Fungal colonies isolated from the lesions and cultured on PDA morphologically resembled the original isolate from the infected pear. In 2014, F. avenaceum was first reported in the United States to cause post-harvest decay of apples in Pennsylvania (Kou et al. 2014). In the Netherlands, F. avenaceum has been reported to cause postharvest decay of 'Conference' pears but was observed at low frequencies (1-5%) in packing-house surveys (Wenneker et al. 2016). Fusarium spp. was also recently found on European pears in Southern Oregon (KC and Rasmussen 2020). F. avenaceum can produce mycotoxins which is a concern for fruit processing (Munkvold et al. 2021). Monitoring for this pathogen to prevent losses and mycotoxin contamination of processed fruit products will be import for consumer safety. To our knowledge, this is the first report of F. avenaceum causing postharvest decay of European pear in the Mid-Atlantic region of the United States.

Oxidation of Organic Compounds Using Water as the Oxidant with H2 Liberation Catalyzed by Molecular Metal Complexes.

ConspectusOxidation reactions of organic compounds play a central role in both industrial chemical and material synthesis as well as in fine chemical and pharmaceutical synthesis. While traditional laboratory-scale oxidative syntheses have relied on the use of strong oxidizers, modern large-scale oxidation processes preferentially utilize air or pure O2 as an oxidant, with other oxidants such as hydrogen peroxide, nitric acid, and aqueous chlorine solution also being used in some processes. The use of molecular oxygen or air as an oxidant has been very attractive in recent decades because of the abundance of air and the lack of wasteful byproduct generation. Nevertheless, the use of high-pressure air or, in particular, pure oxygen can lead to serious safety concerns with improper handling and also necessitates the use of sophisticated high-pressure reactors for the processes.Several research groups, including ours, have investigated in recent times the possibility of carrying out catalytic oxidation reactions using water as the formal oxidant, with no added conventional oxidants. Along with the abundant availability of water, these processes also generate dihydrogen gas as the reaction coproduct, which is a highly valuable fuel. Several well-defined molecular metal complexes have been reported in recent years to catalyze these unusual oxidative reactions with water. A ruthenium bipyridine-based PNN pincer complex was reported by us to catalyze the oxidation of primary alcohols to carboxylate salts with alkaline water along with H2 liberation, followed by reports by other groups using other complexes as catalysts. At the same time, ruthenium-, iridium-, and rhodium-based complexes have been reported to catalyze aldehyde oxidation to carboxylic acids using water. Our group has combined the catalytic aqueous alcohol and aldehyde oxidation activity of a ruthenium complex to achieve the oxidation of biomass-derived renewable aldehydes such as furfural and 5-hydroxymethylfurfural (HMF) to furoic acid and furandicarboxylic acid (FDCA), respectively, using alkaline water as the oxidant, liberating H2. Ruthenium complexes with an acridine-based PNP ligand have also been employed by our group for the catalytic oxidation of amines to the corresponding lactams, or to carboxylic acids via a deaminative route, using water. Similarly, we also reported molecular complexes for the catalytic Markovnikov oxidation of alkenes to ketones using water, similar to Wacker-type oxidation, which, however, does not require any terminal oxidant and produces H2 as the coproduct. At the same time, the oxidation of enol ethers to the corresponding esters with water has also been reported. This account will highlight these recent advances where water was used as an oxidant to carry out selective oxidation reactions of organic compounds, catalyzed by well-defined molecular complexes, with H2 liberation. The oxidation of alcohols, aldehydes, amines, alkenes, and enol ethers will be discussed to provide an outlook toward other functional groups’ oxidation. We hope that this will aid researchers in devising other oxidative dehydrogenative catalytic systems using water, complementing traditional oxidative processes involving strong oxidants and molecular oxygen.

Photochemical degradation of dexamethasone by UV/Persulphate, UV/Hydrogen peroxide and UV/free chlorine processes in aqueous solution using response surface methodology (RSM)

ABSTRACT Dexamethasone (DEX) degradation was investigated using three UV-based advanced oxidation processes combined with sodium persulphate, hydrogen peroxide, and free chlorine in aqueous solutions in a bench-scale reactor. The goal was to determine which process would be the best option in terms of DEX degradation without the subsequent generation of toxic compounds. The process performance for DEX degradation followed the UV/S2O8 2−> UV/H2O2> UV/HOCl order under equal conditions. In the UV/S2O8 2− process, sulphate radicals led to a 70.4% DEX degradation. The experimental mineral inhibitory factors showed that nitrite and bicarbonate further decrease the efficiency of the UV/S2O8 2− process. In the optimal conditions, the UV/S2O8 −2 process removed DEX by 100% and had a 74.1% mineralisation. Furthermore, the intermediates were detected using LC-MS/MS, and the cytotoxicity of the UV/S2O8 −2 process effluent was evaluated using human embryonic kidney cultured cells. The treatment of DEX solution by the UV/S2O8 −2 process significantly decreased the toxicity of the effluent. Therefore, it can be concluded that the UV/S2O8 −2 process can be a reliable process for DEX degradation and detoxification in aqueous solutions.

A conductive silver membrane for electrochemical detection of free chlorine in aqueous solution

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.

Analysis of free chlorine in aqueous solution at very low concentration with lateral flow tests

Test strips are convenient tools for rapid, semi-quantitative analysis of a variety of parameters by dipping them for a few seconds in a sample solution followed by a simple colorimetric read-out. Their sensitivity is mainly determined by the reactivity of the test dyes on the reaction zone and is not sufficient for some applications. The detection limit of commercially available free chlorine test strips, for example, is at present not low enough to confirm the absence of this analyte as disinfectant in rinsing solutions after disinfection or to control required residual amounts of chlorine in drinking water. Therefore, we developed a user-friendly lateral flow test which is capable to detect very low amounts of free chlorine. The latter relies on a larger sample volume passing the reaction zone as compared to simple dip test strips. An amount of as low as 0.05 ppm chlorine can, however, only be detected if oxidation stable flow test substrates are used. The eventually developed flow test reaches a 10x higher sensitivity than a commercial dip test. The result is obtained within 4–5 min flow time, whereby no action is required by the user during this analysis time.

Disposable Chlorine Sensor Based on Pencil Graphite Electrode

Chlorine is widely used as a disinfectant in the water treatment industry for inactivation of pathogenic micro-organisms such as Cryptosporidium and Escherichia coli. Chlorine in aqueous solutions is used for a number of purposes, such as disinfection and bleaching, and also as a powerful oxidizing agent in various manufacturing processes. It is known that chlorine is highly toxic, and additionally it can further react with other substances, such as phenols in environment to produce chlorophenols, which are suspected to be carcinogens. Furthermore, chlorine provides strong and persistent odor, even at low concentrations. In water treatment, the concentration of free residual chlorine should be strictly controlled, namely neither too low nor too high. Free residual chlorine with too low of a level cannot kill pathogenic bacteria and viruses in water effectively to keep water clear and clean. However, free residual chlorine with too high of a level may also be harmful, because the excess free chlorine would react with organic materials existing in the water to produce a large number of undesirable byproducts.1 With increasing public awareness of water quality and tighter public health regulations and practices, such as point-of-use sampling and analysis, a robust, reliable, low-cost, and portable free chlorine sensor would be highly desirable. Several promising materials for free chlorine sensing with linear response have recently been reported in the literature.2-5 However, the sensing materials are either expensive (e.g. glassy carbon, gold, diamond, graphene, carbon nanotubes) or made from potentially hazardous materials (e.g. benzethonium chloride, aniline oligomers).In this work a complete analysis of physical and electrochemical properties of pencil graphite and pencil drawn paper based electrodes has been performed to detect free available chlorine (FAC). Cyclic voltammetry and amperometry were used to study the electro-catalytic properties. Excellent catalytic activity has been obtained for free chlorine detection using both pencil graphite and paper based electrodes with a sensitivity of 50 µAmM-1cm-2 and 29 µAmM-1cm-2 respectively and a linearity range up to 8 mM for both platforms. Also, limit of detect of both electrodes has been found to be 46 and 240 µM, respectively. There is no response obtained for common interfering ions in water such as NO3 -, SO4 2-, CO3 2-, Cl- and HCO3 -. Both the sensors were evaluated for their storage stability and response time and thereby can be applied as a low-cost electrochemical sensor for determining free chlorine in water. Acknowledgment Authors acknowledge financial support from the Ministry of Science & Technology, Bangladesh funded project "FACSens" under the special allocation to Science & Technology Activity (2015/16) programme and Science Foundation Ireland funded project “SweatSens” under the grant agreement No. 14/TIDA/2455. Corresponding authors' email addresses: mamun.jamal@chem.kuet.ac.bd and kafil.mahmood@tyndall.ie Reference Rook, J. J. Water Treat. Exam.1974, 23, 234. S. pan, M. J. Deen and R. Ghosh, Anal. Chem., 2015, 87, 10734-10737. Salazar, P. Martín, M. García-García, F. J. Gonzá lez-Mora, J. L. Gonzá lez-Elipe, A. R. Sens. Actuators, B2015, 213, 116. Olivé -Monllau, R. Orozco, J. Ferná ndez-Sá nchez, C. Baeza, M. Bartrolí, J. Jimenez-Jorquera, C. Cé spedes, F.Talanta2009, 77(5),1739. N. Dossi, R. Toniolo, F. Terzi, F. Impellizzieri, and G. Bontempelli, Electrochim. Acta., 2014, 146, 518–524. Figure 1. (a) SEM image of bare 2B Pencil graphite electrode, (b) EDX of 2B pencil graphite electrode. Figure 1

Determination of trace concentrations of chlorine in aqueous solutions by high-resolution continuum source graphite furnace molecular absorption spectrometry

Trace concentrations of total chlorine were determined by means of molecular absorption of indium mono-chloride (InCl) at 267.217nm using high-resolution continuum source graphite furnace molecular absorption spectrometry. The effects of chemical modifiers and the amount of In on the sensitivity and accuracy were investigated. The optimum pyrolysis and vaporization temperatures were 600°C and 1400°C, respectively. The limit of detection and characteristic mass were found to be 0.10ng and 0.21ng, respectively. Potential non-spectral and spectral interferences were tested for various metals and non-metals at concentrations up to 50mgL−1 and for phosphoric, sulphuric and nitric acids. No spectral interferences were observed. Significant non-spectral interferences were observed with F, Br, and I at concentrations higher than 1mgL−1, 5mgL−1 and 25mgL−1, respectively, which is probably caused by formation of competitive indium halogen molecules. Higher concentrations of mineral acids depressed the signal owing to the formation of volatile HCl. The calibration curve was linear in the range between 0.3 and 10ng with a correlation coefficient of R=0.993. The elaborated method was used for the chlorine determination in various waters and a drug sample.

Redox-Induced Reversible Uptake–Release of Cations in Porous Ionic Crystals Based on Polyoxometalate: Cooperative Migration of Electrons with Alkali Metal Ions

Redox-active porous ionic crystals based on polyoxometalates (POM) were synthesized. By treating the crystal with an aqueous solution of ascorbic acid (reducing reagent) and KCl, one-electron reduction of POM proceeded followed by simultaneous uptake of K+. Interestingly, the reduction did not proceed without KCl, and the molecular size of ascorbic acid was too large to enter the porous crystal lattice. The time courses of reduction and K+ uptake were monitored by UV–vis spectroscopy and atomic absorption spectrometry (AAS), respectively. Both profiles could be reproduced by the linear driving force (LDF) model with similar rate constants. The reduced crystal could be oxidized with aqueous chlorine solution followed by the release of K+, and the redox cycles were reversible. The water sorption properties of the crystals could be controlled by the types of alkali metal ions incorporated. The Cs+ uptake and the simultaneous reduction of the crystal proceeded much faster than in the case of K+, which is in line with the trends in the Gibbs energies of hydration of alkali metal ions. Complete selectivity to Cs+ was observed in the uptake of ions from an aqueous binary mixture of Cs+ and Na+. All these results suggest the cooperative migration of electrons with alkali metal ions and the redox induced ion-exchange in porous ionic crystals based on POM.

Luminescence of triarylphosphines and their application to detection of elemental chlorine in aqueous solution

The concept of aggregation induced emission has been utilized to raise the luminescence of triarylphosphines for the first time.

Kinetic study of hydrogen sulfide absorption in aqueous chlorine solution

Hydrogen sulfide (H2S) is currently removed from gaseous effluents by chemical scrubbing using water. Chlorine is a top-grade oxidant, reacting with H2S with a fast kinetic rate and enhancing its mass transfer rate. To design, optimize and scale-up scrubbers, knowledge of the reaction kinetics and mechanism is requested. This study investigates the H2S oxidation rate by reactive absorption in a mechanically agitated gas–liquid reactor. Mass transfer (gas and liquid sides mass transfer coefficients) and hydrodynamic (interfacial area) performances of the gas–liquid reactor were measured using appropriated physical or chemical absorption methods. The accuracy of these parameters was checked by modeling the H2S absorption in water without oxidant. A sensitivity analysis confirmed the robustness of the model. Finally, reactive absorption of H2S in chlorine solution for acidic or circumneutral pH allowed to investigate the kinetics of reaction. The overall oxidation mechanism could be described assuming that H2S is oxidized irreversibly by both hypochlorite anion ClO− (k=6.75×106Lmol−1s−1) and hypochlorous acid ClOH (k=1.62×105Lmol−1s−1).

Perchlorate Production by Photodecomposition of Aqueous Chlorine Solutions

Aqueous chlorine solutions (defined as chlorine solutions (Cl(2,T)) containing solely or a combination of molecular chlorine (Cl(2)), hypochlorous acid (HOCl), and hypochlorite (OCl(-))) are known to produce toxic inorganic disinfection byproduct (e.g., chlorate and chlorite) through photoactivated transformations. Recent reports of perchlorate (ClO(4)(-)) production-a well-known thyroid hormone disruptor- from stored bleach solutions indicates the presence of unexplored transformation pathway(s). The evaluation of this potential ClO(4)(-) source is important given the widespread use of aqueous chlorine as a disinfectant. In this study, we perform detailed rate analysis of ClO(4)(-) generation from aqueous chlorine under varying environmental conditions including ultraviolet (UV) light sources, intensity, solution pH, and Cl(2,T) concentrations. Our results show that ClO(4)(-) is produced upon UV exposure of aqueous chlorine solutions with yields ranging from 0.09 × 10(-3) to 9.2 × 10(-3)% for all experimental conditions. The amount of ClO(4)(-) produced depends on the starting concentrations of Cl(2,T) and ClO(3)(-), UV source wavelength, and solution pH, but it is independent of light intensity. We hypothesize a mechanistic pathway derived from known reactions of Cl(2,T) photodecomposition that involves the reaction of Cl radicals with ClO(3)(-) to produce ClO(4)(-) with calculated rate coefficient (k(ClO4-)) of (4-40) × 10(5) M(-1) s(-1) and (3-250) × 10(5) M(-1) s(-1) for UV-B/C and UV-A, respectively. The measured ClO(4)(-) concentrations for both UV-B and UV-C experiments agreed well with our model (R(2) = 0.88-0.99), except under UV-A light exposure (R(2) = 0.52-0.93), suggesting the possible involvement of additional pathways at higher wavelengths. Based on our results, phototransformation of aqueous chlorine solutions at concentrations relevant to drinking water treatment would result in ClO(4)(-) concentrations (~0.1 μg L(-1)) much below the proposed drinking water limits. The importance of the hypothesized mechanism is discussed in relation to natural ClO(4)(-) formation by atmospheric transformations.

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.

Correlation between barrier layer Tg and a thin-film composite polyamide membrane's performance: Effect of chlorine treatment

► We measured chlorine-induced T g changes of the barrier layer on a RO membrane. ► We compared the T g change and the performance degradation of the membrane. ► The correlations between T g and performance depend on the pH and Cl concentration. In this study we report changes in the glass transition temperature ( T g ) of the polyamide barrier layer (PBL) of a commercial RO membrane as a function of chlorine treatment in which concentration and pH were systematically varied. The results indicate a monotonic decrease of T g with increasing exposure time at a given chlorine concentration. Further, both the degree and the rate of T g decrease vary significantly with both the chlorine concentration and pH value of the aqueous chlorine solution. Moreover, the decrease in PBL T g correlates well with the reduction in the salt rejection of the membrane, but the magnitude of the correlation is specific to chlorine concentration and pH values.

Modeling Penicillium expansum resistance to thermal and chlorine treatments.

Apples and apple products are excellent substrates for Penicillium expansum to produce patulin. In an attempt to avoid excessive levels of patulin, limiting or reducing P. expansum contamination levels on apples designated for storage in packinghouses and/or during apple juice processing is critical. The aim of this work was (i) to determine the thermal resistance of P. expansum spores in apple juice, comparing the abilities of the Bigelow and Weibull models to describe the survival curves and (ii) to determine the inactivation of P. expansum spores in aqueous chlorine solutions at varying concentrations of chlorine solutions, comparing the abilities of the biphasic and Weibull models to fit the survival curves. The results showed that the Bigelow and Weibull models were similar for describing the heat inactivation data, because the survival curves were almost linear. In this case, the concept of D- and z-values could be used, and the D-values obtained were 10.68, 6.64, 3.32, 1.14, and 0.61 min at 50, 52, 54, 56, and 60 degrees C, respectively, while the z-value was determined to be 7.57 degrees C. For the chlorine treatments, although the biphasic model gave a slightly superior performance, the Weibull model was selected, considering the parsimony principle, because it has fewer parameters than the biphasic model has. In conclusion, the typical pasteurization regimen used for refrigerated apple juice (71 degrees C for 6 s) is capable of achieving a 6-log reduction of P. expansum spores.

Synthesis and characterization of synthetically useful salts of the weakly-coordinating dianion [B12Cl12]2−

The closo-dodecahydrododecaborate [NEt3H]2[B12H12] has been prepared on a lab scale by an improved synthesis from cheap and readily available starting materials Na[BH4] and I2 in diglyme (diethylene glycol dimethyl ether). Subsequent chlorination with elemental chlorine in aqueous solution at normal pressure yielded the per-chlorinated weakly coordinating [B12Cl12]2- anion. By simple metathesis reaction a variety of useful salts [cation]2[B12Cl12] (cation=[NEt3H]+, [NBu4]+, Li+, Na+, K+, Cs+) is available. These salts are useful starting materials, which have the potential to open up the chemistry of [B12Cl12]2- as a weakly coordinating dianion. Exemplarily, they were used in further reactions to prepare [NO]2[B12Cl12], [PPN]2[B12Cl12], and [CPh3]2[B12Cl12]. The crystal structures of Cs2[B12Cl12].SO2, [CPh3]2[B12Cl12].2C2H4Cl2, and [CPh3]2[B12Cl12].2SO2 and preliminary crystal structures of [NO]2[B12Cl12].SO2 and [PPN]2[B12Cl12].CH2Cl2 were determined. The crystal structure of the SO2 solvate Cs2[B12Cl12].SO2 is related to the crystal structure of solvent free Cs2[B12Cl12]. [CPh3]2[B12Cl12].2C2H4Cl2 and [CPh3]2[B12Cl12].2SO2 have very similar structures in the solid state. In both cases the [CPh3]+ cations form only very weak contacts to the [B12Cl12]2- anion and SO2 or C2H4Cl2 solvent molecules respectively. The averaged experimental B-B (178.7 pm) and B-Cl (178.9 pm) bond lengths within [B12Cl12]2- are essentially unchanged in all determined structures and are reproduced well by PBE0/TZVPP quantum chemical calculations (B-B 178.6 pm, B-Cl 179.3 pm). All results indicate that [B12Cl12]2- is a readily accessible weakly-coordinating dianion.