Oxychlorine Species Research Articles

Experimental constraints on the formation of oxychlorine species by UV irradiation and mechanical pulverization on the lunar surface

Experimental constraints on the formation of oxychlorine species by UV irradiation and mechanical pulverization on the lunar surface

Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for molecular evolution on Mars

Mars is a particularly attractive candidate among known astronomical objects to potentially host life. Results from space exploration missions have provided insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to its toxicity. However, it can also provide potential benefits, such as producing brines by deliquescence, like those thought to exist on present-day Mars. Here we show perchlorate brines support folding and catalysis of functional RNAs, while inactivating representative protein enzymes. Additionally, we show perchlorate and other oxychlorine species enable ribozyme functions, including homeostasis-like regulatory behavior and ribozyme-catalyzed chlorination of organic molecules. We suggest nucleic acids are uniquely well-suited to hypersaline Martian environments. Furthermore, Martian near- or subsurface oxychlorine brines, and brines found in potential lifeforms, could provide a unique niche for biomolecular evolution.

Kinetic and mechanistic understanding of chlorite oxidation during chlorination: Optimization of ClO2 pre-oxidation for disinfection byproduct control

Chlorine dioxide (ClO2) applications to drinking water are limited by the formation of chlorite (ClO2–) which is regulated in many countries. However, when ClO2 is used as a pre-oxidant, ClO2– can be oxidized by chlorine during subsequent disinfection. In this study, a kinetic model for the reaction of chlorine with ClO2– was developed to predict the fate of ClO2– during chlorine disinfection. The reaction of ClO2– with chlorine was found to be highly pH-dependent with formation of ClO3– and ClO2 in ultrapure water. In presence of dissolved organic matter (DOM), 60-70% of the ClO2– was transformed to ClO3– during chlorination, while the in situ regenerated ClO2 was quickly consumed by reaction with DOM. The remaining 30-40% of the ClO2– first reacted to ClO2 which then formed chlorine from the DOM-ClO2 reaction. Since only part of the ClO2– was transformed to ClO3–, the sum of the molar concentrations of oxychlorine species (ClO2– + ClO3–) decreased during chlorination. By kinetic modelling, the ClO2– concentration after 24 h of chlorination was accurately predicted in synthetic waters but was largely overestimated in natural waters, possibly due to a ClO2– decay enhanced by high concentrations of chloride and in situ formed bromine from bromide. Understanding the chlorine-ClO2– reaction mechanism and the corresponding kinetics allows to potentially apply higher ClO2 doses during the pre-oxidation step, thus improving disinfection byproduct mitigation while keeping ClO2–, and if required, ClO3– below the regulatory limits. In addition, ClO2 was demonstrated to efficiently degrade haloacetonitrile precursors, either when used as pre-oxidant or when regenerated in situ during chlorination.

Multiphase Volatilization of Halogens at the Soil‐Atmosphere Interface on Mars

AbstractThe Martian critical zone, especially its soil‐atmosphere interface, may host an active halogen cycle affecting habitability, as inferred from halogen trends observed in situ at Gusev and Meridiani, along with oxychlorine species detected in situ. However, the sinks and sources of the Martian halogen cycle remain poorly constrained, especially for Br, including the broader geographic significance of halogen volatility in soils. Here, we statistically analyze Br, Cl, and S distribution and associated cations in the soils of Gale Crater and compare the results with soils of Gusev Crater and Meridiani Planum. We further place the overall in situ soil trends in the framework of terrestrial natural evaporative halides and Mars‐analog evaporative experiments. We observe three lines of evidence that support preferential volatilization of Br versus Cl and S in Martian soils: (a) Unlike Cl and S, Br abundance decreases from subsurface to surface. (b) Br and Cl abundances correlate strongly at the relatively dust‐free and freshly exposed surface of the active Bagnold dunes, but Br‐Cl correlations weaken and Br concentrations decrease in less mobile surface soil. (c) Laboratory experiments show preferential Br loss over Cl and S under ultraviolet (UV) irradiation, consistent with the observed Br loss relative to Cl in Martian soil samples. Overall, these findings generally suggest that soil serves as a source for volatilized halogens. Specifically, soil‐atmosphere multiphase reaction pathways constitute a crucial component missing from purely gas‐phase photochemical models of the halogen cycle.

Fluorometric analysis of chlorite via oxidation of 9-anthracenecarboxaldehyde

We investigated a simple fluorescence signaling method for the convenient analysis of a practical oxidant—chlorite—via the oxidation of 9-anthracenecarboxaldehyde to the corresponding carboxylic acid. 9-Anthracenecarboxaldehyde exhibited a marked ratiometric fluorescence signaling toward chlorite through manipulating its aggregation-induced emission property. The probe showed high chlorite-selectivity over other oxychlorine species as well as common metal ions, anions, and oxidants. Interference from a closely related oxidant, hypochlorite, was efficiently removed using DMSO as a scavenger. The proposed probe also exhibited a prominent ratiometric response through changes in UV–vis absorption behavior. Among the tested aromatic aldehydes (naphthaldehydes, anthracenecarboxaldehyde, and pyrenecarboxaldehyde), anthracene-based carboxaldehyde exhibited the most pronounced signaling contrast and the fastest signaling speed. The detection limit of chlorite determination was found to be 1.1 × 10–7 M. Exploitation of the probe for the convenient analysis of chlorite in tap water via a recovery test was conducted.

Capacity of Chlorate to Oxidize Ferrous Iron: Implications for Iron Oxide Formation on Mars

Chlorate is an important Cl-bearing species and a strong potential Fe(II) oxidant on Mars. Since the amount of oxychlorine species (perchlorate and chlorate) detected on Mars is limited (<~1 wt.%), the effectiveness of chlorate to produce iron oxides depends heavily on its oxidizing capacity. Decomposition of chlorate or intermediates produced during its reduction, before reaction with Fe(II) would decrease its effective capacity as an oxidant. We thus evaluated the capacity of chlorate to produce Fe(III) minerals in Mars-relevant fluids, via oxidation of dissolved Fe(II). Each chlorate ion can oxidize 6 Fe(II) ions under all conditions investigated. Mass balance demonstrated that 1 wt.% chlorate (as ClO3−) could produce approximately 6 to 12 wt.% Fe(III) or mixed valent mineral products, with the amount varying with the formula of the precipitating phase. The mineral products are primarily determined by the fluid type (chloride- or sulfate-rich), the solution pH, and the rate of Fe(II) oxidation. The pH at the time of initial mineral nucleation and the amount of residual dissolved Fe(II) in the system exert important additional controls on the final mineralogy. Subsequent diagenetic transformation of these phases would yield 5.7 wt.% hematite per wt.% of chlorate reacted, providing a quantitative constraint on the capacity of chlorate to generate iron oxides on Mars.

Chlorate as a Potential Oxidant on Mars: Rates and Products of Dissolved Fe(II) Oxidation

AbstractOxychlorine species are globally widespread across the Martian surface. Despite their ubiquitous presence, the ability of oxychlorine species to serve as oxidants on Mars has largely been unexplored. While perchlorate is kinetically inert, chlorate may be a critical Fe(II) oxidant on Mars. However, the timescale over which chlorate may oxidize Fe(II) and the mineral products formed in Mars‐relevant fluids are unclear. Fe(II) oxidation by chlorate was thus investigated in magnesium chloride, sulfate, and perchlorate fluids under neutral to acidic conditions for different total Fe(II) and background salt concentrations. The results show near‐complete Fe(II) oxidation within approximately 2 to 4 weeks, accompanied by formation of the Fe(III) minerals goethite, lepidocrocite, akaganeite, and jarosite. The Fe(II) oxidation rate and the mineral products depend on Fe(II) concentration, the composition and concentration of the background salt, and the acidity of the solution. Calibration of an existing rate law to lower temperatures well reproduces the observed oxidation kinetics in all fluid compositions and allows prediction of the rate of Fe(II) oxidation by chlorate under diverse Mars‐relevant conditions. Rate comparisons demonstrates that chlorate can oxidize Fe(II) substantially faster than O2and on similar or shorter timescales than ultraviolet light. Notably, chlorate causes rapid oxidation under acidic conditions, unlike other oxidants. Chlorate may thus represent an important abiotic Fe(II) oxidant on Mars. The expected coassociation of chlorate with perchlorate may allow for its percolation into the subsurface during brine migration, leading to oxidation in regions that are cutoff from ultraviolet radiation and atmospherically derived oxidants.

Photostationary State in Photoelectrochemical Generation of Perchlorate: Relevance to Mars

The discovery of abundant perchlorate (ClO4–) on Mars has prompted renewed interest in the production, accumulation, and transport of ClO4– and other oxychlorine species in natural systems. Here, we focus on the role of semiconducting minerals in the photochemical generation and destruction of ClO4– and chlorate (ClO3–). Illumination of single-crystal or nanocrystalline films of titanium dioxide polymorphs, rutile and anatase, in chloride (Cl–) solutions can both generate and destroy ClO4– depending upon starting ClO4– and Cl– concentrations. For single-crystal anatase, we observe an apparent photostationary state, in which ClO4– production and destruction reach a near-steady state. We observe more ClO3– production and less ClO4– at higher Cl– concentrations. An inventory of measured dissolved chlorine (Cl) species indicates that some Cl was lost to a volatile form or dissolved form not measured. Our experiments were performed in an aqueous medium under Earth atmosphere and temperature conditions; further...

Abiotic Reduction of Chlorate by Fe(II) Minerals: Implications for Occurrence and Transformation of Oxy-Chlorine Species on Earth and Mars

Recent investigations have reported a widespread occurrence of chlorate (ClO3–) and perchlorate (ClO4–) throughout the solar system, including terrestrial arid environments. ClO3– and ClO4– are deposited/accumulated at an approximate equal molar ratio, with some exceptions, such as the Antarctica Dry Valley soils (MDV) and perhaps Martian surface material, where ClO4– is the dominate ClOx– species. All known ClO4– production mechanisms produce molar ratios of ClO3–/ClO4– equal to or much greater than 1, suggesting that reduced ratios may be due to post-depositional mechanism(s). The objective of this study was to investigate potential iron-mediated abiotic reduction of ClO3–, similar to transformation mechanisms reported for nitrate (NO3–) by Fe(II) minerals. Three types of Fe(II)-containing minerals, wustite (FeO), siderite (FeCO3), and sulfate green rust (GRSO42–), were investigated in completely mixed batch reactors as potential ClO3– reductants at a range of pH (4–9) and iron mineral concentrations (1...

Chlorate and Other Oxychlorine Contaminants Within the Dairy Supply Chain

The presence of chlorate in milk and dairy products can arise from the use of chlorinated water and chlorinated detergents for cleaning and sanitation of process equipment at both farm and food processor level. Chlorate and other oxychlorine species have been associated with inhibition of iodine uptake in humans and the formation of methemoglobin, with infants and young children being a high-risk demographic. This comprehensive review of chlorate and chlorine derivatives in dairy, highlights areas of concern relative to the origin and/or introduction of chlorate within the dairy supply chain. This review also discusses the associated health concerns, regulations, and chemical behavior of chlorate and chlorine-derived by-products, and provides a summary of mechanisms for their detection and removal.

Removal of lindane wastes by advanced electrochemical oxidation

The effective removal of recalcitrant organochlorine pesticides including hexachlorocyclohexane (HCH) present in a real groundwater coming from a landfill of an old lindane (γ-HCH) factory was performed by electrochemical oxidation using a BDD anode and a carbon felt cathode. Groundwater (ΣHCHs = 0.42 mg L−1, TOC0 = 9 mg L−1, pH0 = 7, conductivity = 3.7 mS cm−1) was treated as received, achieving the complete depletion of the HCH isomers and a mineralization degree of 90% at 4 h electrolysis at constant current of 400 mA. Initial groundwater contains high chloride concentration (Cl0− = 630 mg L−1) that is progressively decreased due to its oxidation to different oxychlorine species: Cl2, HClO, ClO−, ClO2− ClO3− and ClO4− some of them (Cl2, HClO, ClO−) playing an important role in the oxidation of organic pollutants. The oxidation rate of chloride (and its oxidized intermediates) depends on the applied current value. Although some of the species generated from them are active oxidants, the presence of inorganic salts is detrimental to the efficiency of the electrochemical process when working at current densities above 100 mA due to the high consumption of hydroxyl radicals in wasting reactions. The initial organic carbon content is not crucial for the extension of the process but high organic loads are more profitable for cost effectiveness. The addition of a supporting electrolyte to the solution could be interesting since it increases the conductivity, reducing the cell potential and therefore, decreasing the energy consumption.

Radiation-Driven Formation of Reactive Oxygen Species in Oxychlorine-Containing Mars Surface Analogues.

The present study demonstrates that γ-radiolyzed perchlorate-containing Mars soil salt analogues (in a CO2 atmosphere) generate upon H2O wetting the reactive oxygen species (ROS) superoxide radical (O2•-), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). This study also validates that analogue radiolysis forms oxychlorine species that, in turn, can UV-photolyze to •OH upon UV photolysis. This investigation was made possible by the development of a new assay for inorganic-origin O2•- and H2O2 determination and by the modification of a previous assay for soil •OH. Results show that radiolyzed Mg(ClO4)2 generates H2O2 and •OH; and when included as part of a mixture analogous to the salt composition of samples analyzed at the Mars Phoenix site, the analogue generated O2•-, H2O2, and •OH, with •OH levels 150-fold higher than in the radiolyzed Mg(ClO4)2 samples. Radiolyzed Mars Phoenix site salt analogue that did not contain Mg(ClO4)2 generated only •OH also at 150-fold higher concentration than Mg(ClO4)2 alone. Additionally, UV photolysis of the perchlorate γ radiolysis product chlorite (ClO2-) generated the oxychlorine products trihalide (Cl3-), chlorine dioxide (ClO2•), and hypochlorite (ClO-), with the formation of •OH by UV photolysis of ClO-. While the generation of ROS may have contributed in part to 14CO2 production in the Viking Labeled Release (LR) experiment and O2 (g) release in the Viking Gas Exchange (GEx) experiment, our results indicate that they are not likely to be the major contributor to the LR and GEx results. However, due to their highly reactive nature, they are expected to play a significant role in the alteration of organics on Mars. Additionally, experiments with hypochlorite show that the thermal stability of NaClO is in the range of the thermal stability observed for thermally liable oxidant responsible for the Viking LR results. Key Words: Mars-Oxygen-Salts-Radiation-Habitability. Astrobiology 17, 319-336.

Measurements of Oxychlorine species on Mars

AbstractMars landed and orbiter missions have instrumentation capable of detecting oxychlorine phases (e.g. perchlorate, chlorate) on the surface. Perchlorate (~0.6 wt%) was first detected by the Wet Chemistry Laboratory in the surface material at the Phoenix Mars Landing site. Subsequent analyses by the Thermal Evolved Gas Analyser aboard the same lander detected an oxygen release (~465°C) consistent with the thermal decomposition of perchlorate. Recent thermal analysis by the Mars Science Laboratory's Sample Analysis at Mars instrument has also indicated the presence of oxychlorine phases (up to 1.2 wt%) in Gale Crater materials. Despite being at detectable concentrations, the Chemistry and Mineralogy (CheMin) X-ray diffractometer has not detected oxychlorine phases. This suggests that Gale Crater oxychlorine may exist as poorly crystalline phases or that perchlorate/chlorate mixtures exist, so that individual oxychlorine concentrations are below CheMin detection limits (~1 wt%). Although not initially designed to detect oxychlorine phases, reinterpretation of Viking Gas Chromatography/Mass Spectrometer data also suggest that oxychlorine phases are present in the Viking surface materials. Remote near-infrared spectral analyses by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument indicate that at least some martian recurring slope lineae (RSL) have spectral signatures consistent with the presence of hydrated perchlorates or chlorates during the seasons when RSL are most extensive. Despite the thermal emission spectrometer, Thermal Emission Imaging System, Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité and CRISM detection of hundreds of anhydrous chloride (~10–25 vol%) deposits, expected associated oxychlorine phases (>5–10 vol%) have not been detected. Total Cl and oxychlorine data sets from the Phoenix Lander and the Mars Science Laboratory missions could be used to develop oxychlorine versus total Cl correlations, which may constrain oxychlorine concentrations at other locations on Mars by using total Cl determined by other missions (e.g. Viking, Pathfinder, MER and Odyssey). Development of microfluidic or ‘lab-on-a-chip’ instrumentation has the potential to be the next generation analytical capability used to identify and quantify individual oxychlorine species on future landed robotic missions to Mars.

Deposition, accumulation, and alteration of Cl−, NO3−, ClO4− and ClO3− salts in a hyper-arid polar environment: Mass balance and isotopic constraints

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl−, NO3−, ClO4− and ClO3− in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl− and NO3− isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO4−/NO3− ratios and NO3− isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO3−/ClO4− in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO3−, possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ∼10 to 30kyr near the glacier to 70–200kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1millionyears). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization.

Widespread occurrence of (per)chlorate in the Solar System

Perchlorate (ClO4−) and chlorate (ClO3−) are ubiquitous on Earth and ClO4− has also been found on Mars. These species can play important roles in geochemical processes such as oxidation of organic matter and as biological electron acceptors, and are also indicators of important photochemical reactions involving oxyanions; on Mars they could be relevant for human habitability both in terms of in situ resource utilization and potential human health effects. For the first time, we extracted, detected and quantified ClO4− and ClO3− in extraterrestrial, non-planetary samples: regolith and rock samples from the Moon, and two chondrite meteorites (Murchison and Fayetteville). Lunar samples were collected by astronauts during the Apollo program, and meteorite samples were recovered immediately after their fall. This fact, together with the heterogeneous distribution of ClO4− and ClO3− within some of the samples, and their relative abundance with respect to other soluble species (e.g., NO3−) are consistent with an extraterrestrial origin of the oxychlorine species. Our results, combined with the previously reported widespread occurrence on Earth and Mars, indicate that ClO4− and ClO3− could be present throughout the Solar System.

Detection of trace organics in Mars analog samples containing perchlorate by laser desorption/ionization mass spectrometry.

Evidence from recent Mars missions indicates the presence of perchlorate salts up to 1 wt % level in the near-surface materials. Mixed perchlorates and other oxychlorine species may complicate the detection of organic molecules in bulk martian samples when using pyrolysis techniques. To address this analytical challenge, we report here results of laboratory measurements with laser desorption mass spectrometry, including analyses performed on both commercial and Mars Organic Molecule Analyzer (MOMA) breadboard instruments. We demonstrate that the detection of nonvolatile organics in selected spiked mineral-matrix materials by laser desorption/ionization (LDI) mass spectrometry is not inhibited by the presence of up to 1 wt % perchlorate salt. The organics in the sample are not significantly degraded or combusted in the LDI process, and the parent molecular ion is retained in the mass spectrum. The LDI technique provides distinct potential benefits for the detection of organics in situ on the martian surface and has the potential to aid in the search for signs of life on Mars.

Oxychlorine species suppress postsurgical adhesions in rats

BackgroundSurgically induced adhesions complicate up to 100% of abdominal surgeries. Food and Drug Administration–approved treatments are generally not only less effective than desired but they also have major contraindications. Oxychlorine species, including chlorine dioxide (ClO2), suppress scar formation in infected wounds without affecting keratinocytes while reducing fibroblast proliferation. The aim of the present study was to evaluate the effect of oxychlorine solutions containing ClO2 on adhesion formation. MethodsMale Wistar rats were subjected to Buckenmaier model of surgical adhesions and treated with either oxychlorine solutions containing ClO2 (40–150 ppm) or isotonic saline solution. To increase the severity of adhesions, peritonitis was produced by intraperitoneal administration of a diluted nonlethal dose of feces (50 mg/kg). Wound strength of the healed wound was measured to evaluate the effects of oxychlorine solutions. In addition, an oxychlorine solution of lesser efficacy (at 100 ppm) was compared with three available anti-adhesion materials. ResultsReproducibility of the model was validated in 26 rats. Oxychlorine solutions containing ClO2 (40–110 ppm) significantly reduced postsurgical adhesion formation without affecting the strength of the healed wound. Higher concentrations (120 and 150 ppm) had no effect. Fecal peritonitis significantly increased, and solutions with ClO2 at 110 ppm significantly reduced adhesion formation. The effect of the oxychlorine solution was significantly greater than that of Interceed, Guardix, Seprafilm, and isotonic saline solution. ConclusionsClO2-containing oxychlorine solutions could be an innovative strategy for the suppression of surgical adhesion formation, with the additional advantage of contributing antiseptic properties.

Characteristics of perchlorate formation via photodissociation of aqueous chlorite

Environmental context. Perchlorate, a well-known thyroid disruptor with both man-made and natural sources represents a major environmental problem in the United States but little information is available concerning the source of natural perchlorate. Previous research has demonstrated that perchlorate can be produced from exposure of some chlorine compounds to ultraviolet radiation, but no information was available how quickly or comparatively how much perchlorate was formed. The results of the present study can be used to evaluate the potential impact of ultraviolet processes on the overall occurrence of perchlorate in the environment. Abstract. The present study provides new and important information on perchlorate (ClO4–) formation through ultraviolet (UV) photodissociation of unbuffered chlorite (ClO2–) solutions from the standpoint of kinetics under three different wavelength regimes having maximum emissions, λe,max, at 235.7, 300 and 350 nm. ClO4– production rates and yields were in general found to be inversely related, with higher yields and lower rates at higher wavelengths, and vice versa. A simple kinetic model for ClO4– production as a function of the ClO2– first-order decay constant and starting concentration was fitted to the experimental data, resulting in the calculation of a rate constant, k2, which is a function of light-source characteristics. Further, a conceptual scheme for ClO4– formation via photochemical reactions between oxychlorine species was proposed based on the experimental results and available literature. The present study is a further step towards understanding the formation of ClO4– from the photolysis of its precursors.

Sequential Flow Injection Determination of Chlorine Species Using a Triiodide-selective Electrode Detector

A flow injection analysis (FIA) method for the determination of four residual chlorine species, namely combined available chlorine (CAC), free available chlorine (FAC), total available chlorine (TAC) and chlorite (ClO2-) was developed using a flow-through triiodide-selective electrode as a detector. An important strategy of speciation studies utilized the kinetic discrimination of reactions between the CAC and FAC with Fe2+, which was applied to the speciation of FAC, CAC and TAC. The speciation of available chlorine species and chlorite (an oxychlorine species) was achieved by using the same set-up, but using flow streams of different pH. The effects of the pH of the carrier stream, the flow rate and the sample volume were studied. The method exhibited linearity from 2.8 x 10(-6) to 2.8 x 10(-4) M active chlorine (expressed as OCl-) with a detection limit of 1.4 x 10(-6) M. The selectivity of the method was studied by examining the minimum pH for the oxidation of iodide by other oxidants, and also by assessing the potentiometric selectivity coefficients. The proposed method was successfully applied to the determination of chlorine species in tap water, and disinfecting formulations where good agreement occurred between the proposed and standard methods were found.

The Use of Naphthol Green for the Determination of Chlorine Dioxide in Water

The determination of chlorine dioxide using Naphthol Green was investigated in the presence of various chlorinated species that can occur under normal water treatment conditions. Ammonium sulfamate (0.75 mol L−1) was used as a masking agent. Naphthol Green selectively reacts with 0–13 mg L−1 ClO2 at pH 9, yielding a linear response (0.9991) with a limit detection of 0.1 mg L−1 ClO2. Several species, , , ClO−, and free available chlorine (FAC), were studied as potential interferents using this method. There was found to be less than 2% interference due to 85 mg L−1 FAC, 23 mg L−1 ClO− and excess of other oxychlorine species could be tolerated without interference.